Contamination of the urine specimen with protein
containing fluids (some of the protein is almost always albumin)
can cause a false positive in all of the below methods (vaginal
discharge, semen, mucopus, pus, blood). Sample's specific gravity: a
trace of protein in a dilute urine is almost always more significant
than trace positivity in a dilute urine. Additional types of testing
may be needed to determine significance of a positive or elevated
urine protein test (electrophoresis, immunofixation, immunodiffusion,
For "microalbuminuria screening", our Community
Medical Center labs use the "Chemstrip Micral dipstick assay" which
brackets results at: neg., 20 mg/dl, 50 mg/dl, and 100 mg/dl. It
actually has a sensitivity to albumin as low as 0-10 mg/dl of urine.
This test method is set so that a patient's urine
albumin complexes with a soluble "gold-anti-albumin antibody" conjugate
on the test strip. The resulting immunocomplex leaves the zone
of excess conjugate and migrates to the detection zone where a
color change is caused (from white to red) in proportion to the
albumin level. Refrigerated specimens hold OK for up to 2 weeks;
do not freeze.
For "microalbuminuria semi-quantitative screening",
our Community Medical Center labs use the "Chemstrip Micral
dipstick assay" which brackets results at: <30 mg alb/g
creat., 30-300 mg alb/g creat., >300 mg/g (>300 indicates
clinical albuminuria or overt nephropathy or macroalbuminuria).
This test produces good, linear results to as low as 1-15 mg alb/dl
urine; the quantitative test is sensitive
to as low as 0.5-30 mg alb/dl of urine.
By comparison, the routine urinalysis at our CMCs
uses the "Multistix 10SG" which is an albumin detector
whose sensitivity detects albumin concentrations as low as 15-30
mg/dl. False positives can occur in highly alkaline urine
and/or urine samples going into containers with residues of disinfectants
containing quarternary ammonium compounds or small amounts of chlorohexidine. False
negatives can occur when proteins OTHER than albumin are present!