Proteinuria
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).
Differential Diagnosis of Proteinuria
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 |