A study on urinary protein excretion as an index of physical exertion Part I: A micromethod for determination of urinary protein with special reference to preservation of urine specimen

The present paper concerns the semi-quantification and micro-quantification of urinary proteins with emphasis on the application of them to the public health area for determining illness, industrial poisoning and physical fitness. The present experiments were designed to examine the relationship between the results in the reading of urinary protein levels by a dip-stick method and the levels measured by micro-quantification using the trichloroacetic acid-Ponceau S reagent method (P-S method). The effects of the preservation of urine specimens on the levels measured by the above methods were also examined. The results were as follows: 1. Although the dip-stick method was useful for the semi-quantification of urine specimens with protein levels above 30mg/dl, readings below 30mg/dl were uncertain. Levels measured by the P-S method had a range of 1.6mg/dl to 8.0mg/dl. For the micro-quantification of urinary protein in the above cases, the P-S method was suitable because of it's low detection limit (1.0mg/dl protein concentration) and of little discrepancy between the sensitivity to albumin and globulin. 2. The readings of the dip-stick method coincided in 80% of urine specimens preserved for 22days in a feezer at -20℃ with their initial readings. On the other hand, the protein levels measured by the P-S method below 30mg/dl varied from the initial ones after the preservation airtightly at room temperature, at 4℃ in a refrigerator and even at -20℃ in a freezer for a day or more. In the case of urine specimens which contained 30mg/dl protein or above, no significant change was observed after the preservation in a refrigerator or a freezer. The destruction of various cell components in urine might cause the variation, in contrast to albumin that is destroyed little during preservation. The author concludes that the protein concentration of urine specimen with a dip-stick reading below 30mg/dl should be measured as soon as possible by the P-S method, when a detailed quantification is required.