Defined as urinary protein excretion > 150 mg/day
Some excreted protein is normal
20% is low molecular type such as Ig
40% is high molecular weight albumin
40% is mucoproteins secreted by tubules
Barriers to excretion begin in glomerulus
Proteins cross to tubular fluid in inverse proportion to their size and negative charge
Smaller proteins are largely reabsorbed
Dipstick analysis
Trace = 10-20 mg/dL
1+ = 30 mg/dL
2+ = 100 mg/dL
3+ = 300 mg/dL
4+ = 1000 mg/dL
Causes of false-positive dipstick for proteinuria
Gross hematuria
Alkaline or concentrated urine
Semen
Presence of WBCs
Benign causes (may f/u 48 hr later)
Fever
Intense activity/exercise
Dehydration
Emotional stress
Acute illness
Management
If trace to 2+
Repeat dipstick on morning voids x2 over next month; if negative: no further w/u; if positive proceed to protein quantification
If 3+ to 4+ with inconclusive urinalysis
Proceed to protein quantification
Protein quantification
>2 g/24 hr: glomerular disease--refer to specialist
<2 g/24 hr: further workup
Workup
24 hr urine specimen is gold standard quantification test
Microscopic analysis of urine sediments
Fatty casts, free fat or oval fat bodies suggest nephrotic range proteinuria (>3.5 g in 24 hr)
Leukocytes and leukocyte casts w/o bacteria suggests renal interstitial disease
