Urine tests can sometimes give false results, meaning they show a problem when there isn't actually one (false positive) and similarly do not correctly determine a problem when there is one (false negative). This can happen for different reasons as explained below.
False Positives on a Urine Protein Test
Urine tests can sometimes give false-positive results for different reasons, such as if the urine is too old or if certain substances or medications are present. Also, if the test is not used properly or if the urine container is not sterile or properly cleaned, it can also give a false-positive result. So, it's important to take these factors into account when interpreting urine test results.
For the urine protein test, false-positive results may occur in highly buffered alkaline urine, which may result from alkaline medication or stale urine. If the dipstick is left in the urine for too long, the chemicals (buffers) on the reagent pads may wash out, resulting in the strip turning blue or green, even if the protein is not present.
Detergents, antiseptics, and quaternary ammonium compounds used to clean the urine container can also result in false positives. Therefore, collecting urine samples in clean, sterile containers is highly recommended. Certain medications and substances, such as phenazopyridine, polyvinylpyrrolidone, and chlorhexidine gluconate (commonly found is skin cleansers), may also cause false positives. Additionally, the presence of blood or high levels of bilirubin may interfere with the accuracy of the test.
Alkaline urine, highly pigmented urine, or concentrated urine (with high specific gravity) can also cause false positives.
False Negatives on a Urine Protein Test
False-negative results can occur in dilute urines and when proteins other than albumin are present in slightly elevated concentrations.
Urinalysis strip (dipstick) is a narrow plastic strip which has several square-shaped pads of different colors attached to it. Each small pad represents a component of the test used to interpret urinalysis. When dipped in the urine, pad colors change in response to the chemical characteristics of the urine. The color changes are noted at specific time intervals and compared against the reference color chart/key.