Laboratory Artifacts in Clinical Medicine: A Review.

Laboratory artifacts-spurious or incorrect results-harm patients when they lead to inaccurate diagnosis and inappropriate clinical management. Although artifacts can seem random, many are explicable with knowledge of laboratory test mechanism and physiology. In this review for the practicing clinician, we illustrate this point using 4 of the most common tests in hospitalized patients-serum chemistry, complete blood count, coagulation testing, and urine drug screening-and the most frequent artifacts they report. We searched the PubMed database for articles before March 21, 2025, supplementing with personal libraries and references of selected articles, choosing topics based on clinical relevance. Pseudohyperkalemia can be due to release of intracellular potassium such as in in vitro hemolysis, leukocytosis, thrombocytosis, imperfect phlebotomy technique, delayed sample transport, and contamination by additives. Pseudothrombocytopenia can be due to EDTA-induced platelet clumping. Unexpectedly low platelet counts should be verified with manual smear and retested with an alternative anticoagulant when clumping is present. Artificially prolonged coagulation assays can be seen when drawing through a line previously instilled with heparin or from a vein proximal to anticoagulant infusion and in underfilled blood tubes. When an unexpectedly prolonged coagulation assay is encountered, direct venipuncture of the arm contralateral to the anticoagulant infusion with a fully filled tube will eliminate most sources of error. Most screening urine drug tests are immunoassays and susceptible to artifact. False positives can occur in immunoassays detecting similar but nonidentical molecules or shared metabolites from another drug; false negatives can be caused by rapid elimination of certain drugs and through intentional urine adulteration. We demonstrate the importance of knowledge of test physiology and mechanism to interpreting an unexpected result, an approach that will enable clinicians to prevent, recognize, and mitigate laboratory artifacts not only for these tests but also for many others.