Proteinuria

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Introduction

A healthy adult will normally secrete 40-150 mg/L of protein daily in the urine, with <20 mg/L albumin and <x mg uromodulin (Tamm-Horsfall mucoprotein). Assessing protein can be done in a number of ways, with differences in sensitivity and ease of use. Common means include urine dipsticks and 24 hour urine collection.

Microalbuminuria (30-300 mg/day) can be an early sign of renal disease in people with diabetes or hypertension, suggesting higher rates of cardiovascular morbidity and mortality. It can be picked up be radioimmunoassay, but most dipsticks are not sensitive enough to register microalbuminuria.

Proteinuria becomes abnormal at >300 mg/d. People with more than 3.5g/day have, in most cases, glomerular disease. ACE inhibitors, or ACE-ARB combinations, are useful at preventing progression of protein levels (need ref here).

The Case of...

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Differential Diagnosis

Functional proteinuria can occur following fever, exercise, congestive heart failure, or stress. It is benign and transient, lasting for hours to a few days.

Orthostatic/postural proteinuria is a benign, intermittent condition in which protein is usually present at <1 g/day and only when upright. It can be confirmed by nocturnal urine collection when the patient is supine.

Nephrotic syndrome is characterized by increased glomerular permeability and over 3.5 g protein/day, and has a long list of differential diagnoses.

Overflow proteinuria is due to an increased serum level of small MW proteins which overwhelms tubular reabsorption capacity. It results from...

Causes of proteinuria, with suggested further investigations, include:

cause	investigation(s)
exercise	urine sample on waking to be repeated without exercise 1-2 days before
diabetic nephropathy	blood glucose levels; other evidence of diabetic complications
urinary tract infection	mid-stream urine sample and culture
congestive heart failure	breath sounds; edema; JVP
multiple myeloma	CBC; serum/plasma protein electrophoresis
amyloid	biopsy; Congo red staining to look for associated splenomegaly
pregnancy	hCG pregnancy test
vaginal mucous contaminant	repeat, with sterile technique