How Medications Can Affect Laboratory Test Results

How Medications Can Affect Laboratory Test Results


Medications and_laboratory_test

Thyroid medications

Cholesterol test

Preanalytical factors and laboratory test

Biological factors and laboratory test

Technical errors and laboratory test results


Total Reading Time: 7 Minutes

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 tests.<1>C:UsersumersDownloads1. Medical Lab Testing Results (

how medications affect lab 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.<2>



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.

Medication and blood test results

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. <3>

The following tests are commonly done to interpret the response of these medications:

  • TSH
  • T3
  • T4

What is TSH?

TSH is a thyroid-stimulating hormone made by the pituitary organ after it tests thyroid chemicals' coursing levels. The pituitary organ reacts to low thyroid chemical degrees by producing more TSH and significant thyroid chemical degrees by producing more TSH as a rule.


Hyperthyroid states (an excessive amount of thyroid chemical, for example, Grave's sickness

Rarely, an under-working pituitary organ (different chemicals will be off also)

High TSH

Hypothyroid states (too minimal thyroid chemical), including progressed Hashimoto’s.

Typical TSH

Good wellbeing with no thyroid chemical issues

It may be in starting Hashimoto's immune system thyroid.

Maybe on account of the pituitary under-working.

Learn all about your thyroid and TSH levels using the ultimate thyroid cheat sheet.

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. <1>

Cholesterol Medications and Lab Results

Cholesterol medications and laboratory test

How medications affect your cholesterol test results?

A cholesterol test is done to decide if your cholesterol is high and detect your danger of having cardiovascular failures and different types of coronary illness and infections of the veins.

Some medications you are taking for other ailments, for example, hypertension or hormonal treatments, may antagonistically influence your lipid levels. This could incidentally build your fatty oils and "terrible" LDL cholesterol while bringing down your "great" HDL cholesterol.

This may be bothersome if you have never had to worry about high cholesterol before. Additionally, if you are currently on medications to lower your cholesterol, you might notice that your therapy may need to be adjusted.

Beta-blockers are medications that are typically endorsed to treat hypertension. Despite the favorable critical benefits they offer in treating a few types of coronary illness, beta-blockers additionally have been noted to diminish HDL levels and elevate triglyceride levels.

Prednisone is a glucocorticoid used to reduce the swelling, warmth, and tenderness associated with many inflammatory conditions. Despite the relief they may give to you, they can raise triglycerides, LDL cholesterol levels, and HDL cholesterol levels.

Your doctor may recommend fasting before having your cholesterol checked. If they say you should fast, they'll likely suggest that you avoid eating for 9 to 12 hours before your test. For this reason, cholesterol tests are often scheduled in the morning. <6>

Non-Medical factors and laboratory tests.

Some preanalytical or "non-medical" in vivo factors are outside our ability to control. These incorporate age, hereditary factors, ethnic groups, race, and sex. These elements can likewise influence your laboratory test results and must be overseen by suitable reference limits for every populace.

Numerous preanalytical variables can be affected by the normalized arrangement of you or must be considered to interpret individual laboratory test results. Research shows that pre-analytical errors have a high risk of altering laboratory test results.

The most common of these factors are diet, starvation, exercise, and posture.


Your standard 2900 J (700 kcal) meal increases the levels of triglycerides by 50%, aspartate aminotransferase by 20%, bilirubin and glucose by 15%, and alanine aminotransferase by 10%. The total protein levels, albumin, and cholesterol are also increased but only by less than 5%, not clinically significant.

Caffeine consumption can also increase blood glucose concentration due to increased gluconeogenesis and increases non-esterified fatty acids even threefold. The latter can interfere with the quantification of hormones and drugs bound to albumin by the fatty acid-induced displacement effect.

Furthermore, plasma renin activity and catecholamine concentrations are elevated after caffeine intake. Apart from these, the acute effects of alcohol include decreased serum glucose and increased serum lactate due to gluconeogenesis inhibition. Alcohol intake may lead to metabolic acidosis because of lactate and acetate (a metabolite of ethanol), which decrease serum bicarbonate.


After 14 h of starvation, your P-hydroxybutyrate concentrations, lactate, acetoacetate, and pyruvate, begin to increase. Hunger of 40-48 h increases the concentration of P-hydroxybutyrate up to 30-fold. Free fatty acids and glucagon are also grown, and insulin is slightly decreased. Metabolic acidosis results from increases in organic acids. Long-term starvation of 4 weeks decreases strongly (20-50%) the concentrations of glutamyl transferase, triglycerides, and urea, whereas it increases (20-40%) the uric concentrations acid, creatinine, and aspartate aminotransferase. Prolonged starvation also invalidates the oral glucose tolerance test due to decreased glycogen stores in the liver. Hunger of 12 hrs is recommended as a standard procedure before sampling, but more extended starvation should be avoided.


Physical exercise changes plasma volume due to volume shifts between the intranasal and interstitial compartments and volume loss by sweating. Additionally, the acid-base balance may be strongly affected. As a result of exercise, the volume of urine decreases, and the erythrocyte and leukocyte count of urine and the number of proteins excreted to urine may increase.

However, the exercise-induced changes show high individual variability and depend on the training status, temperature, and liquids intake.

Non Medical Factors and Labs


There are a few research articles that show posture can affect hormones. For example, a study was done on the cobra pose in yoga in 2004 and published in the journal of human physiology.

What they found was surprising. After only 5 minutes of holding the cobra pose the following happened in all subjects:

Cortisol decreased by 11%

Testosterone increased by 16%

If you are a woman and reading this about testosterone - fear not - you may want to see why testosterone is so important in women.

Biological factors and laboratory tests.

There are sure variations in laboratory test results that can be required because of non-modifiable biological components, for example, age, biological rhythms, and physiological changes during pregnancy. These variables might be controlled for, for example by choosing the most proper time in the day, month, or year for a test, or might be contemplated in the interpretation of laboratory test results.

Following are the biological factors that affect the laboratory test results:

Aging process

The physiological changes related to aging imply that more aged individuals are bound to have laboratory test results that fall outside of the typical reference range. For certain tests, laboratories can give an age-changed reference range, yet for different tests, an outcome outside of the reach in a more established patient should be deciphered with regards to their by and large clinical picture.

Most of the time, accessing the rate and greatness of change after some time offers more data than deciphering the estimation of an individual outcome. Frequently the population range of a test shows significantly more variety than that for an individual patient, for example, serum creatinine, liver compounds. In such cases, the patient's own past outcomes are a helpful pattern.

So while interpreting the laboratory test results in older aged people, laboratories should use suitable reference values related to their age.

Daily and seasonal variation

In addition to the day-to-day variation, your circadian rhythm affects your laboratory test results such as serum somatotropin, adrenocorticotropin, and cortisol show the most substantial circadian change. The diurnal variation in somatotropin is 300-400% and in cortisol 180-200%. The concentrations of adrenocorticotropin and cortisol are highest early in the morning.

Sleeping causes significant peaks in prolactin and somatotropin excretions. The circadian rhythm also affects serum testosterone, thyrotropin, total thyroxine, aldosterone, renin, epinephrine, norepinephrine, hemoglobin, eosinophils, iron, potassium, and phosphate.

Seasonal variations are less significant, but, for example, total thyroxine, triiodothyronine, and thyrotropin response to thyroid releasing hormone are higher in the winter, and 25- hydroxycholecalciferol is higher in the summer.


Your normal pregnancy is characterized by major physiological adaptations altering maternal blood biochemistry and hematological laboratory values. During pregnancy, your mean plasma volume rises about 2600-3900 mL causing hemodilution. There is an overall decrease in total plasma protein concentration, resulting primarily from the decreased albumin concentration.

An increase in the acute-phase proteins, main fibrinogen, leads to an increase in the erythrocyte sedimentation rate. Estrogen increases the hepatic synthesis of binding and carrier proteins (e.g., sex hormone-binding globulin, thyroxine-binding globulin, and corticosteroid-binding globulin), increased total cortisol and total thyroxine. <5>

Technical Errors and laboratory test results

Site of sampling and form of specimen

The site of sampling may now and then significantly influence your laboratory test results. It must be considered, for instance, in glucose examination. It has been indicated that in the fasting state, the arteriovenous distinction in blood glucose is unimportant, yet that after ingestion of glucose, the slender glucose levels rise higher than the venous levels.

In this manner, for instance, the glucose resistance test has specific reference limits for slender and venous examples. Likewise, it is essential to utilize slender bars to evade level bends in the lactose resistance test and erroneously low blood glucose ascends in sound people. The type of example is likewise significant; for instance, the degree of glucose is roughly one mmol/L higher in plasma and serum than in whole blood.


Hemolysis should be avoided to get reliable laboratory test results because numerous constituents estimated in plasma have moderately high concentrations in platelets—hemolysis increments, particularly the concentrations of potassium (up to 3 mmol/L) lactate dehydrogenase.

Storage of samples

The blood sample's centrifugation and separation should preferably be carried out within one h from drawing the sample. Whole blood samples should not be stored. Samples should be protected from light and contact with air. The effect of temperature varies on different analytes.

Errors in urine collection

Timed urine collections required for quantitative examination are particularly at risk of mistakes because, frequently, a piece of the sample is absent. It is additionally regular that urine tests are excessively old or weakened, inspecting vials are contaminated, and preanalytical factors are deficiently thought to be. During this period, urine is also infected with blood.

Mixing up of samples

In most laboratories, special attention is paid to identifying patients and samples, and identification guidelines are available. However, mixing up samples or patients is possible and must be kept in mind in unexpected laboratory results. <7>

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  1. Medical Lab Testing Results (
  2. Drug effects on clinical laboratory tests - ScienceDirect
  3. Biochemical Testing of the Thyroid: TSH is the Best and, Oftentimes, Only Test Needed – A Review for Primary Care (
  4. T4 + T3 combination therapy: any progress? (
  5. Preanalytical and analytical factors affecting laboratory results - PubMed (
  6. Triglycerides - Understand the Test & Your Results (
  7. Diagnostic Errors and Laboratory Medicine – Causes and Strategies (
  8. Postural Influences on the Hormone Level in Healthy Subjects: I. The Cobra Posture and Steroid Hormone
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