Urine Protein: Multistix

The protein pad on the multireagent dipstick (Multistix^®) is based on the "protein error of pH indicator dyes". Basically, the test is dependent on the ability of amino groups in proteins to bind to and alter the color of acid-base indicators, even though the pH is unchanged. The reaction is extremely sensitive to albumin (as it contains the most amino groups), but is much less sensitive to globulins. It is insensitive to Bence-Jones proteins. Generally this differential sensitivity is not a significant problem (nearly all cases of significant proteinuria involve albuminuria).

Interpretation

The urine protein results should always be interpreted in context with the urine specific gravity and pH. Normal urine contains little protein; negative to trace reactions are usual in concentrated urine. A trace to 1+ reaction in a very dilute urine is suggestive of significant proteinuria. A dipstick protein reaction > 2+ in concentrated or dilute urine indicates significant proteinuria. There are numerous causes of proteinuria, the most common of which are urinary tract inflammation, hematuria, and glomerular disease.

False positive results

• Alkaline urine: False positives occur rarely in highly buffered or alkaline urine samples as the citrate buffer is overcome, resulting in a shift in pH. Titration of the sample to a more neutral pH and retesting is indicated. (see discussion under "PROT-SSA").
• Contact time: Leaching of the citrate buffer occurs if the urine remains in contact with the pad for a long time.
• Detergents: Quaternary ammonium compounds and chlorhexidine can result in false positives.

• Bence- Jones proteinuria: A positive SSA protein reaction, with a negative dipstick protein reaction, in a dog or cat with a high index of suspicion for multiple myeloma, is suggestive of the presence of free light chains in the urine.

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Last Updated: Friday, January 15th, 1999