Determination of the protein concentration in canine urine.

There are many laboratory methods which can assist the clinician in the diagnosis of renal disease. One of the most important is the determination of proteins in urine, for which many methods are available (MARTINEK, 1970). In this country in veterinary medicine one of the most widely used tests is heat coagulation at acid pH (HENRY, CANNON and WINKELMAN, 1974). The results are expressed as (negative), (trace), (+), (+ +), etc. They are based on the degree of turbidity and flocculation of the treated sample in comparison to non-treated urine. The main disadvantage of this method is the subjectivity of the reading of the results. Othcr widely used tests are the paper-strip tests (Albustix: Ames Company. Div. of Miles Labs., Elkhart, Ind., U. S. A.) in which the reagents (indicator and buffer) are incorporated in a dried form on a strip of filter paper. The test is based on the protein error of indicators. At the p H of the buffer of the strip most of the bromphenol blue indicator is in the yellow, non-ionized acid form (HI), with only a small portion in the blue ionized form (I -). If protein is present, it will bind with the I--form. This anion has a greater affinity for the protein than for the hydrogen ion. The removal of Iwill cause more of the indicator acid to ionize and the concentration of HI will decrease, resulting in a change of the ratio I-/HI. The color presented by the paper strip will depend on the relative proportions of the two forms. The quantity of the indicator is fixed and, if sufficient protein is present, the larger fraction of the indicator will be in the colored form. The greater the quantity of protein, the dceper blue will be the hue of the indicator strip. As the quantity of buffer is relatively small, applying the strip to strongly buffercd urine samples or to samples with a high pH will give false positive readings. This test compares favourably with the other usual qualitative tests (BRADLEY and BENSON, 1969) but the method was developed for human urine. Its sensitivity is greater for albumin than for other urinary proteins (hemoglobin, BenceJones proteins and mucoproteins). BRADLEY and