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Medical Procedures: The Informed Consent Gap

Echocardiograms, MRI contrast, anesthesia, surgical interventions: the risks that are documented but rarely disclosed.

Rev. Allie Johnson

Sanctified Healer · Monastic Medicine Practitioner

This article has 5 parts. Part 1 of 5: Echo

The Test Is Rarely the Risk. What It Leads to Is.

Most heart tests are offered one at a time, each described as simple. An ultrasound. A quick scan. A stress test. What almost nobody is shown is the whole path: which result leads to which next test, and where that path usually ends.

This section goes through the common heart tests in the order people tend to meet them. For each one it separates two things: what the test itself can do to the body, and what the result tends to set in motion. Some of these tests carry very little direct risk. Others carry real, documented risk. Knowing which is which is the part that gets left out.

"Before any heart test, one question does most of the work: what will you do differently depending on the result?"

What Can Change a Heart Test Result

A heart test is a snapshot of the heart in whatever state the body is in that day. Several ordinary things can shift the reading, and some of them can make a healthy heart look diseased or hide a real problem. People are rarely asked about them before the result is read.

What you ate, drank or took

  • Coffee and other caffeine before a drug stress test. Caffeine blocks the same receptor the stress drugs regadenoson and adenosine act on. In a study on the drug's own label, 200 or 400 mg of caffeine taken 90 minutes before the test cut the number of blood-flow defects detected by about 60%, so a real problem can be missed. The label says to avoid caffeine for at least 12 hours (Lexiscan label). That includes tea, cola, chocolate, energy drinks and some pain relievers.
  • Energy drinks and the ECG. An ECG (electrocardiogram) is the tracing of the heart's electrical signal. In a randomized trial of 34 healthy young adults, 32 ounces of an energy drink lengthened the QT interval, the part of the tracing that shows the heart resetting between beats, by up to 18 to 20 milliseconds, against 12 with a placebo, a look-alike drink with no active ingredients. Blood pressure rose as well (Shah et al., Journal of the American Heart Association, 2019). A long QT is a finding doctors act on.
  • Coffee and extra beats. In a trial of 100 healthy adults wearing heart monitors, days with coffee did not bring more early beats from the upper chambers, but did bring more early beats from the lower chambers, called premature ventricular contractions, and less sleep (Marcus et al., New England Journal of Medicine, 2023). If you are wearing a heart monitor, your caffeine intake is part of the result.
  • ⚠️ Biotin supplements and the heart attack blood test. Troponin is the blood test used to detect a heart attack. The FDA has warned, in 2017 and again in November 2019, that biotin (vitamin B7, sold in high doses for hair, skin and nails) can make some troponin tests read falsely low, so a heart attack can be missed. The FDA received a report of a death in a person taking high-dose biotin whose troponin result was falsely low (FDA, Biotin Interference with Troponin Lab Tests; report on the 2019 FDA safety communication). Tell the lab and the emergency room if you take biotin or a B-complex.

The state your body is in

  • Low thyroid. An underactive thyroid can slow the heart rate, shrink the size of the ECG signal, lengthen the QT interval, stiffen the heart's relaxation on echo, and cause fluid around the heart. A study of 68 people with hypothyroidism documented these ECG and echo changes (Sawarthia et al., Cureus, 2023), and a case report describes a weakened, enlarged heart that recovered on thyroid treatment (Madan et al., BMJ Case Reports, 2015). Low thyroid also raises cholesterol. These are small studies.
  • Thick blood. Hematocrit is the share of blood made up of red cells. A German population study found that it "profoundly affects" how the heart's main chamber fills on a Doppler echo (the part of the scan that measures blood flow), with higher hematocrit going with slower early filling (Schunkert et al., Journal of Hypertension, 2000). Dehydration concentrates the blood, so the two often arrive together.
  • Low minerals. Low potassium is the most common mineral abnormality in clinical practice. Its mark on the ECG is an extra wave after the T wave, and combined with certain drugs it lengthens the QT interval and can set off a dangerous rhythm (El-Sherif and Turitto, Cardiology Journal, 2011). Water pills are a known cause: the label for furosemide lists low potassium, low magnesium and low calcium among the imbalances to watch for (Lasix label).
  • Low sodium. Low sodium is not known to change the ECG or echo directly. It matters as a signal: about 20% to 27% of people admitted with heart failure have low sodium, and in a large US registry they were more likely to die in hospital (6.0% against 3.2%) (OPTIMIZE-HF registry, summarized in PMC4497331). Thiazide water pills and drinking far more water than the body needs are both known causes.
  • Weak kidneys. In the same study of 586 people without coronary disease, lower kidney function was among the predictors of a raised troponin, and sepsis was the strongest (Yang et al., Medicine, 2017). Doctors look at whether the level is rising across repeat tests, not at one number.

Medicines that change heart tests

Many common medicines change the ECG or another heart test. The QT interval matters most here: when it grows too long, the heart can slip into a dangerous rhythm called torsades de pointes. One independent registry lists more than 220 drugs in its QT risk categories and keeps the list current at crediblemeds.org (CredibleMeds, as described in Cardiovascular Toxicology, 2022).

This is a reason to bring a complete list of everything you take, including supplements, to any heart test. It is never a reason to stop a medicine on your own. Whether to hold or change anything is a decision for the prescriber.

  • Medicines with FDA warnings about the QT interval. The antidepressant citalopram (the FDA advised against doses above 40 mg a day, or 20 mg over age 60), the anti-nausea drug ondansetron, and the antibiotic azithromycin all carry FDA safety warnings about QT lengthening (FDA Drug Safety Communications of August 2011 and March 2012 for citalopram, June 29, 2012 for ondansetron, and March 12, 2013 for azithromycin; Celexa label; FDA azithromycin communication).
  • Other groups on the QT lists. The citalopram label itself names examples it should not be combined with: the heart rhythm drugs quinidine, procainamide, amiodarone and sotalol, the antipsychotics chlorpromazine and thioridazine, the antibiotics gatifloxacin and moxifloxacin, and pentamidine and methadone (Celexa label).
  • The risk stacks. Two QT-lengthening medicines together, or one taken while potassium or magnesium is low, add up. An ECG read without the full medicine list is missing part of the picture.
  • Acid reflux drugs and magnesium. In March 2011 the FDA warned that prescription proton pump inhibitors (such as omeprazole) can cause low magnesium when taken for long periods, in most cases over a year, and that low magnesium can cause irregular heartbeat. In about a quarter of the cases reviewed, magnesium supplements alone did not correct it and the drug had to be stopped (FDA Drug Safety Communication, 2011).
  • Water pills. These lower potassium and magnesium, which changes the ECG as described above.
  • Medicines that slow the signal. Digoxin's own label says normal doses can lengthen the PR interval, the delay between the upper and lower chambers firing, and can produce false positive changes on an exercise test (Lanoxin label). Beta blockers slow the heart rate and that same signal; on the label for sotalol, a heart rate under 50 occurred in 13% of people. Lithium most often flattens or inverts the T wave, a change that can also be read as a heart problem (review of lithium and the ECG).
  • Warfarin and the calcium score. Warfarin blocks a vitamin K dependent protein that keeps calcium out of artery walls. In one study of 266 people, the 133 on warfarin-type drugs had significantly more calcified plaque in their heart arteries than 133 matched people who were not (Schurgers et al., PLoS One, 2012), though not every study agrees (systematic review, Frontiers in Cardiovascular Medicine, 2022). Statins raise the score as well, as covered below.
  • Medicines that interfere with a stress test. The label for the stress drug regadenoson says methylxanthines, "e.g., caffeine, aminophylline and theophylline, interfere with the activity" of the drug, and that dipyridamole, a blood thinner, "may increase" it and should be withheld for at least two days beforehand when possible (Lexiscan label). Beta blockers blunt the heart's response to exercise and dobutamine tests. Imaging centers give instructions on what to hold.

None of this means a result should be dismissed. It means the result is read alongside a blood count, thyroid, minerals and what you had that day. If those have not been checked, it is fair to ask for them before an abnormal reading is treated as heart disease.

Echocardiogram: What Is and Is Not Documented

An echocardiogram (often called an echo) is an ultrasound of the heart. A handheld probe on the chest sends sound waves in and builds a moving picture from the echoes. A full exam usually takes 30 to 60 minutes. Nothing is injected in a standard echo and there is no radiation.

Here is where the evidence stands. The professional body for medical ultrasound states that "no independently confirmed adverse effects caused by exposure from present diagnostic ultrasound instruments have been reported in human patients in the absence of contrast agents." The same statement says that biological effects have been reported in animal studies, and that higher output or longer exposure "can increase the likelihood of bioeffects" (American Institute of Ultrasound in Medicine, Prudent Clinical Use and Safety of Diagnostic Ultrasound, revised May 29, 2024).

No published human study shows that a standard echo weakens the heart, lowers its pumping strength, releases markers of heart muscle injury, or triggers abnormal rhythms. That is different from proof that nothing happens. Studies designed to measure the heart immediately before and after a routine echo are scarce, so the question has largely not been asked.

What the lab and animal studies do show

  • In cells in a dish. Cells that line blood vessels showed signs of oxidative stress after 15 to 30 minutes of continuous exposure from a clinical heart scanner. The authors concluded that "cardiac ultrasound of current clinical diagnostic use increases intracellular oxidative stress on endothelial cells in vitro" (Basta et al., Cardiovascular Research, 2003). A dish of cells has no blood flow to carry heat away and no tissue in front of it, and the beam was held still, which a real exam does not do.
  • In rats. Specially timed ultrasound pulses, designed to pace the heart, lowered the heart rate by about 20% in ten rats, an effect that lasted at least 15 minutes, with no apparent gross damage to the heart tissue (Buiochi et al., 2012). A later study of 60 rats by the same group, which calls the method "cardiovascular therapeutic ultrasound," found drops in the heart's output after exposure (Coiado et al., 2022). These were deliberate stimulation experiments, not diagnostic scans.
  • What that adds up to. Ultrasound is not biologically inert. At high enough intensity, or held still long enough, it affects living tissue. It has not been shown to happen to a human heart in an ordinary echo.

The limits the machines are built to

  • The FDA sets maximum output for diagnostic ultrasound machines. For heart imaging the application-specific limit is 430 milliwatts per square centimeter (a measure of how much sound energy lands on an area over time), with an overall ceiling of 720, and a Mechanical Index no higher than 1.9 (FDA, Marketing Clearance of Diagnostic Ultrasound Systems and Transducers, February 21, 2023).
  • These are ceilings for the machine, not the dose a heart receives. Actual exposure is usually lower and changes as the probe moves.
  • The same guidance asks manufacturers to explain any Thermal Index above 6. Doppler modes, used to measure blood flow, run at higher output than plain imaging, which is why the ultrasound society asks operators to keep exposure "as low as reasonably achievable."

What you are still not told

  • Every ultrasound machine shows two safety numbers on its screen: the Thermal Index (an estimate of how much the sound could warm tissue) and the Mechanical Index (an estimate of its physical force on tissue). They are there so the operator can keep exposure as low as the exam allows. Patients are almost never told they exist.
  • The FDA's own wording is more cautious than "it's just sound waves." Its ultrasound page says the waves "can heat the tissues slightly" and can "produce small pockets of gas in body fluids or tissues," and then: "The long-term consequences of these effects are still unknown" (FDA, Ultrasound Imaging, updated September 2024). The FDA classes ultrasound as non-ionizing, meaning it does not break chemical bonds the way X-rays do.
  • Repeated exposure is not tracked. People with heart failure or valve disease may have an echo every year for decades. No one adds up the total, and whether repeated exams have any combined effect has not been studied in a way that could answer the question.
  • An echo often finds small things that are common and harmless, such as a slightly leaky valve. Each finding can lead to repeat exams or further tests.

Diagnostic and treatment ultrasound are not the same dose

  • Ultrasound is also used to destroy tissue on purpose. High-intensity focused ultrasound (HIFU) concentrates sound on a point a few millimeters wide and holds it there. The tissue at that point is heated above 60°C, which kills cells within about a second (An Introduction to High Intensity Focused Ultrasound, Journal of Clinical Medicine).
  • The intensities are far apart. Diagnostic machines are capped at 0.72 watts per square centimeter, averaged over time (FDA guidance, 2023). Treatment fields have been measured at up to 24,000 (Canney et al., Journal of the Acoustical Society of America, 2008). That is tens of thousands of times higher. The two figures are measured in different ways, so this is a comparison of scale, not an exact ratio.
  • The delivery is different too. An echo uses short pulses and a beam that keeps moving, so no single spot of heart muscle is exposed for the length of the exam. HIFU keeps its focus on one spot until the tissue is destroyed.
  • What this means. The two share the same physics: tissue absorbs sound and warms, and pressure waves push on it. A diagnostic echo is built to stay below the point where that injures tissue, and HIFU is built to cross it. That ultrasound can destroy tissue at treatment strength does not show that it injures tissue at diagnostic strength.

Stress Echocardiogram: The Risk Is the Stress, Not the Ultrasound

A stress echo is an echo taken while the heart is working hard. The work comes from a treadmill or bike, or from a drug when someone cannot exercise. The most common drug is dobutamine, which acts like a strong dose of adrenaline: it makes the heart beat faster and squeeze harder.

Dobutamine: what the drug does

  • Dobutamine pushes the heart rate toward 85% of the maximum predicted for your age. If an artery is narrowed, the heart muscle can need more blood than that artery can deliver. That shortfall is called ischemia, and producing it is how the test works.
  • Risks documented in the medical literature and the drug's label: dangerous heart rhythms, atrial fibrillation (an irregular, often rapid heartbeat), a sharp drop in blood pressure, heart attack, rupture of the heart wall, and death.
  • How often. In an international registry of 85,997 stress echo exams, a life-threatening event occurred in 1 in 557 exams done with dobutamine (63 of 35,103) and 1 in 6,574 done with exercise (4 of 26,295). Five people died during dobutamine testing, two from a chaotic heart rhythm and three from rupture of the heart wall. None died during exercise testing (Varga, Garcia and Picano, American Journal of Cardiology, 2006).
  • How to read those numbers. The registry was a voluntary questionnaire: 71 of 300 centers answered. People sent for a drug stress test are often sicker than those who can use a treadmill, which accounts for part of the gap. The authors' own conclusion is that the test is safe "but serious complications may occur," and that exercise "seems safer than pharmacologic stress."
  • The drug is not approved for this use. Dobutamine's FDA label approves it for short-term support of a failing heart. Stress testing is not among its approved uses. The label mentions stress testing in one place, as a warning: "Stress cardiomyopathy has been reported with dobutamine in association with cardiac stress testing" (dobutamine label). Stress cardiomyopathy is a sudden weakening of the heart muscle brought on by a surge of stress hormones. Using an approved drug for another purpose is legal and common, and it is called off-label use. It is something a person can be told.
  • If you can exercise, an exercise stress echo carries the risks of hard exertion in a person who may have heart disease, without the drug. It is fair to ask why a drug test is being chosen.

The question underneath

A stress test is designed to find out whether the heart runs short of blood when pushed. For someone with symptoms, that answer can change treatment. For someone with no symptoms, the question is what the answer would be used for, and that belongs in the conversation before the test, not after.

Nuclear Stress Test

In a nuclear stress test, a small amount of radioactive tracer is injected into a vein and a scanner maps how blood flows through the heart muscle, once at rest and once under stress. There are two kinds of scanner. The older and more common one is called SPECT. The newer one is called PET, usually with a tracer called rubidium-82. They differ in the tracer used and in the radiation dose. The stress is nearly always a drug, most often regadenoson (brand name Lexiscan).

What the labels and dose figures say

  • Radiation from a PET scan. A standard rest and stress rubidium PET study gives about 3.7 mSv (millisieverts, the unit for radiation dose to the body), measured in 10 volunteers. The researchers compare that with the 3.1 mSv an average American receives from natural background radiation in a year (Senthamizhchelvan et al., Journal of Nuclear Medicine, 2010). The CT scan used to line up the images adds to it.
  • Radiation from a SPECT scan depends on the lab. A survey of all 7,911 nuclear heart scans done in one week at 308 labs in 65 countries found doses from 0.8 to 35.6 mSv, with a middle value of 10. Only 30% of labs met the recommended level of 9 mSv or less (Einstein et al., European Heart Journal, 2015). Two people having the "same" test can receive doses many times apart. It is fair to ask which scan is being offered and what dose that lab typically delivers.
  • The FDA's 2013 warning. On November 20, 2013 the FDA warned of a rare but serious risk of heart attack and death with both stress drugs, regadenoson and adenosine, and said resuscitation equipment and trained staff should be on hand before either is given (FDA Drug Safety Communication, November 20, 2013).
  • The tracer generator. ⚠️ Both rubidium generators on the US market, CardioGen-82 and RUBY-FILL, carry a boxed warning, the FDA's strongest, for high radiation exposure when the generator is run with the wrong solution or the required testing is skipped (CardioGen-82 label). When that happens, long-lived radioactive strontium can pass into the injection. This is about how the facility runs its equipment, so it is fair to ask how they test it each day.
  • Caffeine can hide a problem. In a study on the Lexiscan label, caffeine taken 90 minutes before the test cut the number of blood-flow defects detected by about 60%. The label says to avoid caffeine for at least 12 hours beforehand. That includes tea, cola, chocolate, energy drinks and some pain relievers.

Coronary Calcium Score

A calcium score is a quick CT scan of the chest that measures hardened (calcified) deposits in the heart's arteries and turns them into a number. Nothing is injected and there is no stress drug. The scan itself is low risk. Most of what matters comes after the number.

What to know before agreeing

  • Radiation is small, and not zero. In 3,442 people in a large US study the average dose was about 1 mSv (Messenger et al., International Journal of Cardiovascular Imaging, 2016). Across 82,214 scans at 33 sites the average was the same, and nearly double, 1.96 mSv, in people with a body mass index over 30 (Patel et al., 2019). Repeat scans add up.
  • With age, a score above zero is the usual result. In 6,110 adults with no known heart disease, the amount of calcium and the share of people with any calcium rose steadily with age, and were higher in men than in women (McClelland et al., Circulation, 2006). One report on the same study puts the share of white men aged 70 to 74 with detectable calcium at about nine in ten (MESA data, reported by TCTMD). Ask for your percentile for your age and sex, not just the number.
  • Zero does not mean no plaque. The scan only sees hardened plaque, not soft plaque. In 25,182 Swedish adults aged 50 to 64, a more detailed scan found plaque in 5.5% of those with a calcium score of zero, and a significant narrowing in 0.4% (Bergstrm et al., Circulation, 2021).
  • Statins raise the score. An analysis of eight trials concluded that "statins promote coronary atheroma calcification," even while the plaque itself shrinks (Puri et al., Journal of the American College of Cardiology, 2015). A rising score in someone taking a statin does not by itself mean the disease is worsening, which makes repeat scans hard to read.
  • What the scan changes. In a trial of 2,137 people with no symptoms, those who were scanned had slightly better blood pressure and cholesterol four years later, and were no more likely to be sent for further heart tests (Rozanski et al., Journal of the American College of Cardiology, 2011).
  • Screening has not been shown to prevent heart attacks or deaths. A 2025 review of the trials concluded: "The available evidence is insufficient to determine whether screening asymptomatic patients" with a calcium score "has an impact on all-cause mortality or CV events" (Scheu et al., BMJ Open, 2025). The score predicts risk well. Whether acting on it changes the outcome is not yet known.

Testing When You Have No Symptoms

Many heart tests are ordered for people who feel fine: before a minor surgery, at a yearly visit, or because a cholesterol number was high. The specialty societies themselves advise against much of this. That advice is published. It is rarely mentioned in the exam room.

  • Stress imaging. The Canadian Cardiovascular Society: "Don't perform stress cardiac imaging or advanced non-invasive imaging in the initial evaluation of patients without cardiac symptoms unless high-risk markers are present." It gives the same advice against repeating these tests every year in people without symptoms (Choosing Wisely Canada, updated September 2025). The American College of Cardiology and the American Society of Nuclear Cardiology made the same recommendation in the US in 2012 (Choosing Wisely).
  • A resting or treadmill ECG. The US Preventive Services Task Force "recommends against screening with resting or exercise electrocardiography (ECG) to prevent cardiovascular disease (CVD) events in asymptomatic adults at low risk." For people at higher risk it says the evidence is insufficient to judge. It found that screening "leads to harms that are at least small and may be moderate, including unnecessary invasive procedures, overtreatment, and labeling" (USPSTF, June 2018).
  • Carotid ultrasound. This is an ultrasound of the neck arteries that supply the brain. The scan itself is harmless. The Task Force "recommends against screening for asymptomatic carotid artery stenosis in the general adult population," and concludes with moderate certainty that such screening "has no benefit and may be harmful" (USPSTF, February 2021). The harm is in what follows a positive scan. Of people sent on for a catheter angiogram in older studies, 0.4% to 1.2% had a stroke caused by that test.
  • What the procedure itself costs. In people with a narrowed neck artery and no symptoms, stroke or death within 30 days occurred in 3.0% of those who had surgery to clear it in one large trial (Halliday et al., Lancet, 2010). In a later trial it was 2.9% with a stent and 1.7% with surgery, a difference that was not statistically significant (Rosenfield et al., New England Journal of Medicine, 2016).

"High-risk markers" is where the judgment sits. Diabetes, known artery disease elsewhere in the body, or strong family history can make a test reasonable in someone with no symptoms. If a test is being offered to you without symptoms, it is fair to ask which markers the doctor is counting.

Where the Path Often Ends: Stents

A stent is a small mesh tube placed inside a narrowed artery to hold it open. During a heart attack, opening the blocked artery quickly saves heart muscle and lives. That is not in dispute. The picture is different for stable disease, meaning narrowed arteries in someone who is not having a heart attack.

What the trials found in stable disease

  • No fewer deaths or heart attacks. In 5,179 people with stable disease and moderate or severe reduced blood flow on testing, going straight to catheterization with stents or surgery did not reduce heart attacks or death over a median of 3.2 years, compared with starting on medication alone. It did relieve chest pain better (ISCHEMIA trial, Maron et al., NEJM, 2020).
  • European guidance says the same. The 2024 European guideline states that in stable patients with normal heart pumping and no major blockage in the main left artery, opening arteries "does not prolong overall survival" compared with medication alone. It is considered when symptoms continue despite medication (summary of the 2024 European Society of Cardiology guideline).

So in someone with stable disease, a stent is mainly a treatment for chest pain that medication has not controlled. If you have no chest pain, it is fair to ask what the stent would be for.

Not all stents are the same

  • Bare-metal stents are plain metal mesh. Drug-eluting stents are coated with a drug that slows tissue from growing back into the stent. In a Norwegian trial of 9,013 people, death or heart attack over six years was the same with either type (16.6% and 17.1%). Repeat procedures were fewer with the drug-coated type: 16.5% against 19.8% (Bønaa et al., NORSTENT, New England Journal of Medicine, 2016).
  • Dissolving stents. The Absorb scaffold was designed to dissolve over time. After approval, longer follow-up showed more clots inside the device and more heart events than with a metal stent. The FDA wrote to heart specialists on March 18, 2017, and again on October 31, 2017, and the maker stopped selling it worldwide that September (FDA letter to health care providers, 2017). People who already have one should know which device they were given.
  • Blood thinners come with every stent. A stent is a foreign surface, and blood can clot on it. Two anti-clotting drugs are prescribed together afterward, and they raise the risk of bleeding. How long they are needed depends on the stent and the person. The 2024 European guideline keeps six months as the default after a stent in stable disease, with shorter courses for people at high risk of bleeding (summary of the 2024 European Society of Cardiology guideline). Ask before the procedure, because it affects any surgery or dental work planned for the following year.

Transesophageal Echocardiogram (TEE)

In a transesophageal echo, the ultrasound probe is passed down the throat into the esophagus (the food pipe), which lies directly behind the heart. This gives a much sharper picture than a probe on the chest. It is used to look at valves, to check for clots before certain procedures, and to guide surgery. Unlike a standard echo, it is an invasive procedure done under sedation, and its risks come from the probe and the sedation.

Risks of the procedure

These are described in a review of the procedure's safety (Hilberath et al., Journal of the American Society of Echocardiography, 2010). We have not listed rates, because they vary with the setting and the person.

  • A tear in the esophagus (rare but documented)
  • Injury to teeth, lips or throat from the probe
  • Breathing stomach contents into the lungs under sedation
  • Spasm of the voice box and other breathing problems
  • Reactions to the sedation drugs
  • Sedation also means you cannot report what you are feeling during the procedure

Cardiac Catheterization & Coronary Angiogram: Contrast and the Kidneys

A coronary angiogram (cardiac catheterization) is an invasive procedure. A thin tube is threaded through an artery in the wrist or groin up to the heart, and iodine-based contrast dye is injected into the heart's arteries so they show up on X-ray. It is used to find blockages and to place stents. It is routinely described as "standard," a word that tends to close the conversation rather than open it.

What contrast dye can do to weak kidneys

  • Contrast dye is cleared by the kidneys. Healthy kidneys filter it out within hours. Kidneys that are already weak clear it slowly, and the dye can injure them further. This is called contrast-associated acute kidney injury.
  • It is a recognized cause of kidney injury in hospital. In a study of 4,622 hospital patients, 7.2% developed some degree of kidney injury during their stay. The four most common causes were reduced blood flow to the kidneys, medications, surgery and contrast dye (Nash, Hafeez and Hou, American Journal of Kidney Diseases, 2002).
  • Fluid load. The dye adds volume and draws fluid into the bloodstream. A heart that is already struggling has to pump that extra volume, and kidneys that cannot clear it prolong the strain.

"It's Standard" Is Not Informed Consent

A patient who declines contrast and is told "it's standard" has not given informed consent. The word positions a protocol as a fact of nature rather than a decision with risks that can be accepted or refused. Standard of care describes what is typically done. It does not remove a person's right to know what that thing does to their body, or to say no.

For someone with weak kidneys, contrast is a known and documented risk. It deserves a real conversation: what is the alternative, what will be done to protect the kidneys, and what happens if the answer is no.

Other risks not routinely disclosed

  • Allergic reactions , from hives to collapse. A previous reaction to contrast raises the risk.
  • Thyroid effects. The iodine load can trigger an overactive thyroid in people with an undiagnosed thyroid condition.
  • Risks of the catheter itself: a tear in the artery wall, artery spasm, stroke from dislodged plaque or air, abnormal heart rhythms, and bleeding or bruising where the tube went in.
  • Death. A US registry of 71,916 people catheterized in 1990 put deaths at 0.11% of diagnostic procedures (Noto et al., Catheterization and Cardiovascular Diagnosis, 1991). That figure is old, and risk depends heavily on how sick the person is.
  • Radiation. The X-ray used throughout delivers far more radiation than a chest X-ray, and long or complex procedures can approach the dose of a CT scan.

The Workup That Is Often Missing: Iron

Heart muscle needs iron to make energy, and blood needs iron to carry oxygen. Too little iron, and too much, both change how the heart performs and how it comes through a procedure. An iron workup is an ordinary blood draw. It is written into the guidelines for heart failure (a condition where the heart cannot pump as well as the body needs). We did not find it listed as a routine part of the workup for chest pain, or before a stress test, a catheterization or a stent.

What a full iron workup includes

  • Complete blood count. Hemoglobin and hematocrit show whether there is anemia (too few red cells or too little hemoglobin to carry oxygen).
  • Serum iron. The iron in the bloodstream at that moment. It swings through the day and after meals, so it means little alone.
  • Total iron-binding capacity (TIBC) or transferrin. Transferrin is the protein that carries iron. When the body is short of iron it makes more of it, so this number rises.
  • Transferrin saturation. This is the ratio: serum iron divided by binding capacity, as a percentage. It shows how much iron is actually on hand for the tissues. Under 20% points to too little available iron.
  • Ferritin. The body's iron store. Ferritin also rises with inflammation, infection, liver disease and heart failure itself, so a "normal" or high ferritin can sit on top of iron that the tissues cannot use.
  • An inflammation marker such as C-reactive protein, so the ferritin can be read correctly.

Ferritin alone is the test most often ordered. Read without the ratio, it misses the pattern that matters most in heart patients: stored iron that looks adequate with a low transferrin saturation.

Why it matters before a heart test or procedure

  • It changes what the tests show. Anemia makes the heart pump harder and can make it look enlarged on an echo, and it can raise troponin without a heart attack (see "What Can Change a Heart Test Result" above).
  • Anemia raises the risk from contrast dye. The standard score for predicting kidney injury after a stent procedure, built from 8,357 patients, counts anemia as a risk factor in its own right, alongside age over 75 and the amount of dye used (Mehran et al., Journal of the American College of Cardiology, 2004).
  • Before heart surgery, anemia is linked to more blood transfusions, longer stays in intensive care and in hospital, and higher rates of complications and death. Iron deficiency without anemia may carry similar risk, though that is less clear (Frei et al., Journal of Clinical Medicine, 2025).
  • Too much iron is also a heart risk. Iron overload can damage heart muscle and disturb its rhythm (Kremastinos and Farmakis, Circulation, 2011). That is one more reason ferritin is read together with the ratio and not alone.
  • In heart failure it is recommended. The 2021 European heart failure guideline recommends that everyone with heart failure be checked periodically for anemia and iron deficiency with a full blood count, ferritin and transferrin saturation, as a Class I recommendation, its strongest (summary of the 2021 European guideline).
  • The cut-offs are different in heart failure. The guideline counts iron as low when ferritin is under 100, or when ferritin is 100 to 299 and transferrin saturation is under 20%. A result marked "normal" on a standard lab range can still meet this definition.

Before a heart test or procedure, you can ask whether a full iron workup has been done, including the transferrin saturation and not only ferritin, and what the numbers were. What to do about a result that is low or high is a separate decision with its own trade-offs, made with your provider.

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