Which factor can cause a false positive urine bhCG result?

• A. Proteins
• B. Aspirin
• C. Blood
• D. Vitamin C

Answer: (A)

Urine pregnancy tests use antibodies to detect hCG. If something in the urine causes non-specific binding or mimics the signal the test is designed to show, a color line can appear even when hCG isn’t present. Proteins in urine can cause this kind of interference by non-specifically interacting with the antibodies or altering the assay environment (pH, ionic strength, flow), leading to a false positive signal.

Aspirin and vitamin C tend to affect the test differently: vitamin C is more likely to reduce the color signal and cause a false negative rather than a false positive, and aspirin is not a common culprit for creating a false positive in standard urine hCG tests. Blood in the urine can also cause interference in some assays, but it’s less consistent as a cause of a false positive.

Thus, proteins in the urine are the most plausible factor that can yield a false positive result in a urine hCG test.