Errors in Laboratory Testing: How Common Substances Can Critically Skew Reported Results

By Maisie Orsillo, OMS IV and Cheryl Rosenfeld, DO, FACE, FACP, ECNU
errors in laboratory testing

If you like your coffee, have a banana every morning, or take vitamins and supplements, you may want to talk to your doctor before obtaining your next set of laboratory tests. Many of the things we eat, drink or take interfere with laboratory testing, and may cause falsely elevated or decreased levels of endocrine tests. To avoid an incorrect diagnosis, pay close attention to any restrictions prior to getting your labs done.


Hair loss, dry, itchy skin, and brittle nails are of concern to many people. To address these problems, individuals may turn to common supplements that claim to support the health of these areas. Hair, skin, and nail supplements contain multiple vitamins, including biotin. Biotin (vitamin B7) is beneficial in the recommended daily amount of 30-70 mcg. However, the quantity of biotin in many supplements may exceed 5,000 mcg! Recent case reports have found that biotin consumption in excess of the recommended amount can interfere with multiple laboratory tests, including thyroid and parathyroid testing.

When the thyroid is functioning normally, thyroid stimulating hormone (TSH) is released from the pituitary gland to stimulate production of thyroid hormones (T3 and T4) from the thyroid to maintain our metabolic rate, heart and neurological function, and macronutrient processing. When someone is not producing enough thyroid hormone (hypothyroidism), their TSH levels will increase as the pituitary tries to stimulate the thyroid gland to produce more thyroid hormone. In contrast, if there’s too much thyroid hormone (hyperthyroidism), TSH levels will fall. When one is taking large amounts of biotin, lab values can display falsely high or low TSH values and falsely high T3 and T4 levels, which may make it appear as though a patient has hyper- or hypothyroidism. These changes occur because the chemicals used to perform thyroid tests in some laboratories contain biotin.

Another thyroid hormone test that can be affected by biotin supplements is calcitonin. A calcitonin test is performed when endocrinologists are looking for a particular type of thyroid cancer called medullary thyroid carcinoma. When someone is taking excessive biotin, the level of calcitonin may be falsely elevated. This may lead to a suspicion of cancer, and additional invasive testing, when no cancer actually exists.

Biotin can also interfere with parathyroid function testing. The parathyroid glands are located behind the thyroid gland and regulate calcium in the body. Parathyroid hormone (PTH) levels will rise when calcium levels fall while PTH production will decrease when calcium levels are elevated. Excess biotin consumption can lead to falsely low PTH levels, making it appear as though a patient has an underactive parathyroid, or may mask the true cause of a patient’s elevated calcium.

These interferences are concerning because it can appear as though a patient has a disease and may even lead to inappropriate treatment by the physician, including unnecessary prescription of medication, use of radiologic testing or even biopsy.

In order to minimize the risk of abnormal lab values it is important for patients to let their physician know all of the medications they are taking, especially multivitamins and additional vitamin, mineral, or herbal supplements. The combination of these medications may lead to increased biotin consumption. If you know you are undergoing blood work for any type of endocrine testing, you should discuss with your provider whether you need to avoid biotin supplements prior to getting your blood drawn and for how long.

"It is important for your health care team to review all of your medications prior to endocrine testing to avoid any difficulties in diagnosis."

Medications, Vitamins and Minerals

Several endocrine tests are affected by medications, so you may be advised to stop a medication prior to testing.

If a chromogranin A test is ordered, you will be advised to avoid some very typical medications for heartburn or reflux. Use of either proton-pump inhibitors, like omeprazole, or H2-receptor blockers, like famotidine, may falsely elevate the chromogranin A levels and lead to unnecessary additional testing or treatment.

When patients are evaluated for a hormonal cause of high blood pressure (excess adrenal secretion of aldosterone or adrenaline, for example), certain blood pressure medications may need to be stopped prior to testing and resumed after testing, or changed to another medication prior to testing. Fortunately, the most commonly used blood pressure medications, like diuretics (“water pills”), alpha and beta blockers, ACE inhibitors, and calcium channel blockers may not interfere with the testing and can be continued.

Just as biotin may interfere with the calcitonin test, there are other medications and supplements which will cause falsely abnormal calcitonin results as well. These include birth control pills, epinephrine (found in an epi-pen), glucagon and calcium.

If you are using a glucometer or continuous glucose monitor, be aware that acetaminophen and high dose vitamin C may cause falsely elevated blood sugar. Doses of vitamin C above 1000 mg daily have resulted in excessive insulin doses and hypoglycemia in many well documented cases. There is evidence that high dose vitamin C may either falsely raise or lower A1c levels, making it difficult to track glucose control long term and possibly lead to over medication. It is wise to check with the manufacturer to determine if your glucose monitoring device is affected by any medications or supplements.

Food, Beverages and Smoking

Endocrinologists may order sa-livary cortisol testing to look for Cushing’s syndrome, where the adrenal glands produce too much cortisol. It is advised that patients refrain from eating, drinking, smoking or using toothpaste or mouthwash for 30 minutes prior to collecting the saliva for the test.

Many foods, alcohol, exercise and smoking will interfere with testing for excess adrenaline in patients with suspected endocrine hypertension. There is no question that quitting smoking is the best thing to improve health, but if you are using nicotine sources in order to quit, such as patches or gum, those will need to be stopped for a period of time before the test. Bananas and citrus fruits will need to be avoided as well. Beverages such as coffee, tea and alcohol will similarly affect the laboratory tests and may need to be withheld for up to 12 hours prior to either blood or urine collection.

It is important for your health care team to review all of your medications prior to endocrine testing to avoid any difficulties in diagnosis. Pay close attention to restrictions in exercise or diet (including fasting) and any instructions you may receive regarding your medications or supplements. By partnering with your medical team, you can help make the right diagnosis and avoid unnecessary medication and testing.