What factors can cause false readings on urine test strips?

Urine tests can sometimes yield false readings, meaning they might indicate a problem when there isn't one (false positive) or fail to detect a problem when there is one (false negative). Several factors can contribute to such inaccuracies, often related to the condition of the urine sample, substances present, or the way the test is conducted.

One common cause of false readings is the presence of certain substances or medications. For example, drugs like Levodopa and Phenazopyridine, as well as high doses of Vitamin C, can lead to false positives for ketones. Similarly, dehydration, high specific gravity of urine, and delayed analysis of the urine sample can also result in false positives for ketones. On the other hand, a high dosage of Vitamin C may cause a false negative for nitrites, while the use of the antibiotic tetracycline can lead to false negatives for leukocytes.

The composition of the urine sample itself can further affect test accuracy. For instance, urine with a pH of 7.5, or the presence of substances like penicillin, pus, semen, or vaginal secretions, may cause false positives for high protein levels in the urine. Additionally, Vitamin C in the urine can interfere with test results, causing false negatives for blood cells and glucose.

Improper handling of the urine sample or test strips can also contribute to inaccuracies. Using non-sterile or improperly cleaned containers can lead to contamination, which may affect test outcomes. Ensuring proper storage and handling of both the urine sample and test strips is crucial for obtaining reliable results.