Zagreb, Croatia—Concerns have been raised about side effects of OTC drugs and dietary supplements or how they might interact with prescription drugs.

A new European study discusses an additional problem with use of the products: how they might affect laboratory test results.

The report in Clinical Chemistry and Laboratory Medicine notes that patients often fail to disclose their OTC product use to ordering physicians or laboratory staff, according to a survey.

Participating in the study were 18 European countries, with 200 outpatients surveyed in each. Respondents were patients who were referred to the laboratory for blood sampling and who voluntarily agreed to participate in the study. Included in the survey were questions about the frequency of consumption of various products, awareness of the importance of informing physicians and laboratory staff about them and information about the influence of preanalytical factors, in general, on laboratory test results.

Results indicate that 68% of patients were regularly taking at least one OTC drug or dietary supplement; vitamins (38%), minerals (34%), cranberry juice (20%), acetylsalicylic acid (17%), and omega fatty acids (17%) were the most common.

The study team points out that those products, if consumed shortly before blood sampling, potentially could cause changes in lab test results, which might make interpretation more difficult and even lead to incorrect diagnoses.

“The use of various OTC drugs and dietary supplements is highly prevalent in Europe and patients are often not willing to disclose this information to the laboratory staff and ordering physician,” the authors emphasize. “The education of both patients and healthcare staff is needed.”

“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,” adds corresponding author Ana-Maria Simundic, PhD, of the Sveti Duh Clinical Hospital in Zagreb, Croatia.

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