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 often caused by diabetes or hypertension. The earlier the kidney disease is diagnosed, the more effective the treatment will be. For higher urine protein levels, the microalbuminuria test is replaced by the measurement of total proteins in the urine, which includes, in addition to albumin, other proteins of clinical interest, such as antibody fragments sometimes called free kappa or lambda light chains, or Bence-Jones proteins.
The protein-to-creatinine ratio is not calculated when the protein level is less than 0.05 grams per litre of urine (< 0.05g/L). A ratio greater than 40 mg/mmol in urine can be benign and caused by infection, medications, vigorous exercise, pregnancy, diet, exposure to cold, emotional or physical stress, or simply a change in posture (orthostatic proteinuria) or by contamination during sample collection. The test must be repeated to ensure its validity. High ratios can also occur in non-renal conditions (hypertension, bone marrow disease [multiple myeloma], lupus, preeclampsia, etc.). A ratio greater than 250 mg/mmol is consistent with nephrotic syndrome, a severe disease of the renal glomerulus.