What can cause false results on a protein urine test?

Urine tests are valuable tools for diagnosing various health conditions, but they can sometimes yield inaccurate results. These inaccuracies are categorized into false positives and false negatives.

False Positives on a Urine Protein Test

1. Old Urine Samples: Urine that has been left standing for an extended period can deteriorate, leading to misleading results. Chemical changes in the urine over time can affect the test's accuracy.
2. Substances and Medications: Certain medications and substances can interfere with the test. For example, alkaline medications or stale urine can alter the chemical balance, causing false positives. Medications like phenazopyridine, used for urinary tract infections, can also cause the test strip to show positive.
3. Improper Use of Test Strips: Leaving the test strip in the urine for too long can wash out the reagents (buffers) on the test pads, causing the strip to change color to blue or green, even if no protein is present.
4. Contaminated Containers: Residues from detergents, antiseptics, or other cleaning agents used on the urine collection container can interfere with the test. It is crucial to use clean, sterile containers for urine samples.
5. Interfering Substances: Substances like polyvinylpyrrolidone (used in some medications) and chlorhexidine gluconate (found in some skin cleansers) can lead to false positives. Additionally, the presence of blood or high levels of bilirubin can affect the test's accuracy.
6. Urine Characteristics: Highly buffered alkaline urine, resulting from alkaline medications or stale urine, can cause false positives. Similarly, highly pigmented urine or urine with high specific gravity can interfere with the test’s accuracy.

False Negatives on a Urine Protein Test

1. Dilute Urine: If the urine sample is too dilute, the concentration of protein may be too low for the test to detect. This can happen if you consume a large volume of fluids before testing, leading to a lower protein concentration in the urine.
2. Other Proteins: The test may not detect proteins other than albumin, which is the primary protein usually measured. Some proteinuria conditions involve proteins that are not detected by standard tests, resulting in a false-negative result despite the presence of abnormal protein levels.