Pathology Associates Of Lexington, P.A.
Pathology Associates Of Lexington, P.A.
Pathology Associates Of Lexington, P.A.
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        Microalbumin "dipstick" Screening Test, Urine
      

The best way to discern small quantities of urinary protein loss that are absolutely elevated is to check for one protein and place it into a ratio with the chemical that defines the effectiveness of kidney function...albumin/creatinine ratio. However, a quick screening test for albumin alone can be used to exclude those who are thereby presumptively "normal". Since there are many trivial as well as important reasons that albumin can be detected in urine, diabetics with positivity of this screening test may be further "baselined" with the quantitative microalbumin test and categorized as to renal  diabetic glomerular status, the first break-point being as below. [back to urine tests, protein]

The American Diabetes Association position statement on diabetic nephropathy states that "microalbuminuria" is present if the ratio exceeds 30mcg alb./mg of creatinine. The threshold for non-micro protein loss (clinical albuminuria) is 300mcg alb/mg creatinine. And, because of the many potential causes of episodes of albumin "leak" into the urine, the classification of a patient should be based on positive findings on several occasions over a 3-6 month period (in other words, diabetic albuminuria is relatively constant...not very intermittent).

General comment:

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, etc.).

Microalbumin Screen:

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.

Microalbumin Semi-Quantitation:

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.

Routine Urinalysis Dipstick Testing:

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!

"Old Timey" Manual Sulfosalicylic Acid Protein Precipitation Test:

This test detects ALL urine proteins (including the protein in hemoglobin)! Its sensitivity is 5-10 mg/dl. False positives can occur with high levels of many medications. False negatives can occur in highly alkaline urine.

(posted 2002; latest update 29 September 2003)

 
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