Only traces of protein should be found in the urine of normal individuals. The presence of proteins, mainly albumin, in the urine is a sign of kidney disease.
The test primarily detects albumin and can produce a negative result in the presence of other proteins. Depending on the urine concentration, a negative result in highly diluted urine does not completely rule out the possibility of kidney disease. This test is also not sensitive enough to detect microalbuminuria, the excretion of very small quantities of albumin marking the very beginning of kidney disease in diabetic or hypertensive patients. The presence of traces of protein is generally of little clinical significance. Protein excretion can vary throughout the day and can reach clearly positive values as a result of exercise, a change in posture (orthostatic proteinuria), emotional stress, heat, certain medications or pregnancy. It is best to always measure proteins in the morning urine to limit these benign variations.
The presence of proteins is generally confirmed by the use of other tests such as microalbumin measurement, quantitative urine protein assay or the Bence-Jones protein test.