Urine total protein

Urine total protein (also known as urine protein or 24-hour urine protein) is used to assess and monitor proteinuria associated with primary glomerular disorders, including minimal change disease, membranous nephropathy, and focal segmental glomerulosclerosis, as well as secondary nephropathies due to diabetes mellitus, systemic connective tissue diseases such as systemic lupus erythematosus, amyloidosis, and other multisystem conditions. The test supports evaluation of renal involvement in individuals at increased risk for chronic kidney disease, assists with risk stratification for chronic kidney disease progression and ischemic heart disease among patients with renal disease, and is used to monitor renal function during therapy with potentially nephrotoxic medications (aminoglycosides, amphotericin B, cisplatin, cyclosporine, nonsteroidal anti-inflammatory drugs, angiotensin‑converting enzyme inhibitors, sulfonamides, penicillins, thiazide diuretics, furosemide).

Proteinuria is an early and sensitive marker of both primary glomerular disease and secondary nephropathies. Under normal conditions, only small amounts of low–molecular weight proteins cross the glomerular filter, and most filtered protein is reclaimed by the proximal tubules, yielding minimal urinary protein excretion of approximately 40–80 mg/day; excretion greater than 150 mg/day defines proteinuria and is predominantly albumin. Transient, functional proteinuria may accompany fever, strenuous exercise, stress, acute infection, or dehydration. Orthostatic proteinuria occurs in a subset of individuals under 30 years of age and is absent in the supine position but appears after prolonged standing or ambulation. Pathologic renal proteinuria is most often glomerular, resulting from disruption of the glomerular basement membrane in settings such as diabetic nephropathy, primary glomerulopathies, connective tissue diseases, poststreptococcal glomerulonephritis, or drug-induced injury, and frequently exceeds 2 g/day. Tubular proteinuria reflects impaired proximal tubular reabsorption, as seen with hypertensive nephroangiosclerosis, urate nephropathy, heavy metal toxicity, Fanconi syndrome, or drug-induced injury, and is usually ≤2 g/day. Protein overproduction leading to overflow proteinuria—such as with hemoglobinuria, myoglobinuria, or monoclonal light chains in plasma cell dyscrasias—is not primarily renal; in these settings, targeted studies like urine protein electrophoresis are indicated. Marked proteinuria (>3–3.5 g/L) can produce hypoalbuminemia, reduced oncotic pressure, and edema. Persistent microalbuminuria (30–300 mg/day) indicates early diabetic nephropathy and correlates with increased risk of ischemic heart disease. A random urine total protein (urine protein) test is appropriate for screening but does not quantify daily excretion; persistent abnormal results should be followed by a 24‑hour urine protein measurement and adjunctive testing to classify the pattern of proteinuria and investigate the underlying cause.