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Principle: The test is based on the „protein error“ principle of indicators. The test zone is buffered to a constant pH value and changes colour from yellow to greenish blue in the presence of albumin. Other proteins are indicated with less sensitivity.
Evaluation: The test strip detects values above 10 mg protein/dl urine. The colour fields correspond to the following ranges of albumin concentrations:
negative, 30, 100 and 500 mg/dl or
negative, 0.3, 1.0 and 5.0 g/l.
Falsely positive results are possible in strongly alkaline urine samples (pH > 9), after infusions with polyvinylpyrrolidone (blood substitute), after intake of medicaments containing quinine, and also by disinfectant residues in the urine sampling vessel. The protein colouration may be masked by the presence of medical dyes (e. g. methylene blue) or beetroot pigments.
Diagnosis: The limit of a physiological proteinuria lies between 10 and 30 mg/dl. It differentiates between:
1) Benign proteinuria is observed after physical strain, orthostatic proteinuria, with fever and during pregnancy. In such cases the protein excretion rate is usually normal in the first morning urine, however in the course of the day values can vary greatly.
2) Extrarenal proteinuria frequently appears with acute diseases like heart insufficiency, colics, liver cirrhosis, plasmocytoma, and carcinomas.
3) Renal proteinuria is caused by increased permeability of the glomerular filter and may indicate pyelonephritis, glomerulonephritis, tuberculosis of the kidneys, kidneys participation at infections and poisonings, cystic kidneys, gouty kidney. Every positive test reaction requires further diagnostic examinations.
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