How Medications Influence Laboratory Test Results - I
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How Medications Influence Laboratory Test Results - I

Many prescription and over-the-counter drugs, as well as dietary supplements, can affect laboratory test results

Post by on Monday, January 31, 2022

First slide

Medications can influence clinical laboratory test results either by interfering with the analytical frameworks themselves or affecting endogenous constituents. Thus, your doctor, clinicians, and laboratory staff should remember this potential interference while interpreting the consequences of laboratory test results and guarantee that they get a total and exact record of all medications being utilized by patients to anticipate potential (drug-lab test interactions).


For instance, biotin is a dietary supplement, and it was seen that it could cause clinically tremendous off-base outcomes on lab tests, for example, troponin. In these tests, biotin can cause erroneously low results, prompting missed conclusions and possibly severe clinical ramifications. Biotin can also mess up your hormone lab tests, causing wrong high results in testosterone, estradiol, and cortisol, inaccurate low results in thyroid-stimulating hormone (TSH), follicle-stimulating hormone (FSH), luteinizing hormone, parathyroid hormone, and human chorionic gonadotropin levels.


Many prescription and over-the-counter drugs, as well as dietary supplements, can affect laboratory test results. It is an important reminder, considering that an estimated 70% of medical decisions made in the United States are based on clinical lab test results. Because incorrect test results can lead to unknown diagnoses and treatment errors that may harm patients, clinicians need to take a careful medical history and know which drugs can affect which results.


Medications and laboratory tests interact

Lab tests play a crucial role in clinical decision-making. More than 4000 lab tests are available, and an estimated 70% of clinical decisions are based on their results. The correct interpretation is critical. The pharmacologic effects of drugs can change laboratory test results; for example, levothyroxine increases thyroid levels, or lisinopril may increase potassium levels in your laboratory test results. But these changes do not involve interference with the laboratory test results. True drug-lab test interactions result from a drug altering the test specimen or direct interference from the drug itself reacting with the test reagents.


Following is the list of medication that interacts with your laboratory tests:


Antibacterial medications can mess up your lab tests, with cephalosporins at the bleeding edge. Cephalosporins can cause false-positive laboratory test results in urine glucose and urine ketone tests, just as in the direct Coombs test (used to recognize immune-mediated hemolytic anemia). Penicillin-type anti-infection medications like amoxicillin and ampicillin can likewise cause wrongly high glucose test results.


Co-trimoxazole, daptomycin, erythromycin, and telavancin can cause false high laboratory test results in prothrombin time (PT) and the international normalized ratio (INR). Doxycycline can cause falsely elevated effects in catecholamine tests. Levofloxacin, ofloxacin, and rifampin can cause false positives in urine drug screenings for opiates. Ciprofloxacin can mildly boost results in urine protein tests.




Psychotropic medications include antidepressants, antipsychotics, and anti-dyskinesia agents, can cause false positives in drug screens and pregnancy laboratory test results.


Contrast media

Iodinated contrast media can affect your blood protein levels, altering the protein blood or protein urine tests. Gadolinium contrast medications can lower your colorimetric measures for serum angiotensin-changing over protein, calcium, and zinc. These medications can likewise cause positive impedance in creatinine, magnesium, selenium, and absolute iron, restricting limit tests and positive and negative iron examination interactions. After contrast media are managed, patients should stand by at any rate for 4 hours before having lab specimen collected.


Proton pump inhibitors

Proton pump inhibitors (PPIs), for example, omeprazole, lansoprazole, dexlansoprazole, rabeprazole, pantoprazole, and esomeprazole, can cause negatives laboratory test results in your urea breath test and the stool antigen test. With long-term use, PPIs can prompt false negative points in the urea breath laboratory test results. A few clinicians have detailed expanded INR and PT in patients getting PPIs and warfarin correspondingly. PPIs can likewise cause raised serum levels of chromogranin A, a marker for tumors.


Medications and laboratory test

Can you take medicine before having a laboratory test? It relies upon the type of blood test you are having and what medication you take. In case you do not know or have any inquiries about your blood test, ask your healthcare provider for guidance. Never stop taking prescribed medication unless you are told to do so by your doctor.


Some medications can influence blood-related laboratory test results, yet this does not imply that you need to quit taking your medication. For instance, oral corticosteroids, for example, steroid tablets, can build your cholesterol levels in a blood cholesterol test. Notwithstanding, a specialist can consider this while interpreting your laboratory test results, so you will not have to quit taking your medication. In case you are uncertain, continue to accept your medication as recommended and check with your doctor. You may likewise need to take your medicines with you to show the individual who will perform your blood test. Herbal remedies, vitamins, or supplements can also affect laboratory test results, so tell your doctor if you take any of these.


When to stop taking a medication

It would help if you never stopped taking prescribed medicine unless you’re told to do so by your doctor. Sometimes, you may need to stop taking medication before a blood test.


Testing your medicine

If you have a blood test to check whether your medicine is working, you should keep taking your medication in most cases. For example, suppose you are taking medicine to lower your cholesterol level. In that case, you should keep taking it before your cholesterol blood test. As a result, it will show whether the treatment is working.





Thyroid medications and laboratory test

Are You Taking Thyroid Medications? How to Get Accurate Tests?

We have heard many complaints regarding incorrect fluctuations in laboratory test results after the reduction of thyroid medications. And a common question of patients is that, should I take my medication before having my blood drawn for a thyroid test? Yes, you can, but to get more accurate laboratory test results, the test should be done when the thyroid hormone medication is taken after the thyroid test, not before.


Lab tests for thyroid

It is recommended to test your thyroid function if you start taking medications to control your hypothyroidism levels. And the test should be done after 4 to 6 weeks when you start taking medications. The following tests are commonly done to interpret the response of these medications:

TSH, T3, T4


Taking synthetic T4 medication

These medications deliver gradually and consistently, bringing about a moderately stable chemical level in your body. Its half-life is nine days, implying that if you do not take any more medicine, it requires nine days to free half from it from your body. Blood tests are influenced like this: TSH and free T3 are the same as whether you take your T4 medication previously or have held as long as 48 hours to take the blood test. T4 tops 2 hours after taking it in medication to influence a blood laboratory test results when taken during that pinnacle time. For the more significant part of the remainder of the day, the T4 levels will be stable.


A few specialists change portions of medication dependent on TSH, so all things considered, no distinction. If the blood test’s understanding incorporates T4, the prescription and blood test’s circumstance should be regarded for an exact evaluation.


Taking combination medication that includes T3

This is the place where we see the hugest contrast in the circumstance of your precise laboratory test results. Suppose you somehow managed to take your thyroid drug within 5 hours of completing your thyroid function tests. In that case, your laboratory test results may show that you are ingested too much, in any event, when you might be precisely dosed, or they may demonstrate your labs to be inside specific cutoff points when you may be under-dosed.


What happens is that the TSH is immediately affected by the T3 in the medication. It starts to drop directly and drops for 5 hours after taking the dose of medicine. It begins to rise and reaches a stable point about 13 hours after taking the medication. This can vary in people, but the cited research study found that this can be expected in most people. T3, being the active form of the thyroid hormone, acts differently than T4 in that it has a relatively short half-life. Within 18 hours to 3 days, depending on the person, half of the T3 hormone is left compared to 9 days for T4. Therefore, levels of T3 can fluctuate during the day, in some rapidly declining within the day.


When you take T3 in medicine, the free T3 levels on a blood test are influenced promptly by expanding. The pinnacle is around 4 hours in the wake of taking medication. At that point, it begins the decay. Consequently, it is generally best to defer your mixed drug until after you complete your lab test. It appears to be the best is completing your thyroid capacity tests before anything else, carrying your medications with you, and taking them just after you have your thyroid function tests to guarantee that you get exact test outcomes.


(To be continued…)


(The Author is Microbiologist Certified infection control Auditor, Kidney Hospital Srinagar. Email:

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