Interference by analgesic and antirheumatic drugs in 25 common laboratory assays.

Twenty five different analytical procedures, commonly used in clinical laboratories, were investigated for interference by eight analgesic and antirheumatic drugs. Ten of the investigated assays showed no statistically significant interference. Acetylsalicylic acid interfered in six assays (for glucose, uric acid, protein and cholesterol). Aminophenazone significantly decreased glucose, bilirubin and protein values, whereas caffeine affected four methods (for glucose, protein and iron). No definite influence of phenobarbital could be detected on any assay. Glucose, uric acid and iron values were altered in the presence of diclofenac. Indomethacin interfered in glucose, urea, uric acid and protein assays. Samples containing ibuprofen had altered creatinine, bilirubin and iron values, whereas ketoprofen interfered in glucose and iron determination.