OTC drugs, supplements can skew lab test results

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American and European consumers swallow a vast quantity of over-the-counter (OTC) drugs and dietary supplements but they often fail to tell their doctors what they’re taking — and that can skew the results of vital lab tests.

A new study of patients in 18 European countries found that those taking OTC products and dietary supplements are not aware of the potential effects on laboratory test results they may have. In addition, patients do not believe that they need to disclose this use to medical and laboratory staff.

The study found that dietary supplements and OTC drugs are more frequently used by middle-aged patients — especially women — with the most common being multivitamins, multiminerals, cranberry and aspirin.


All of these compounds, if consumed shortly before blood sampling, may cause changes in lab test results, thus leading to interpretation difficulties and possibly incorrect diagnoses.

Although more data is needed about the frequency of the consumption of various dietary products, vitamins or OTC drugs, the authors of the study believe that a multifaceted approach is necessary to draw attention to the issue using educational interventions which target both healthcare professionals and patients.

“We hope that our survey helps to raise awareness about this need to educate patients about the potential effect of OTC drugs and dietary supplements on lab test results, and we would encourage clinicians and lab staff to engage more with their patients and ask them direct questions about the use of various self-prescribed products,” said Professor Ana-Maria Simundic of the Sveti Duh Clinical Hospital in Zagreb, Croatia, and the corresponding author of the article, published in Clinical Chemistry and Laboratory Medicine.

About the Author

Truman Lewis
Truman has been a bureau chief and correspondent in D.C., Los Angeles, Phoenix and elsewhere, reporting for radio, television, print and news services, for more than 30 years. Most recently, he has reported extensively on health and consumer issues for ConsumerAffairs.com and FairfaxNews.com.