Effects of low and high relative molecular protein mass on four methods for total protein determination in urine.

Four commonly used methods for the determination of total protein in urine were compared. These were two biuret methods using different precipitants, a Ponceau S method and a Coomassie Brilliant Blue method. The protein content of the urines was also evaluated by sodium dodecylsulphate polyacrylamide gel electrophoresis. The biuret method with ethanolic phosphotungstic acid as precipitant correlated best with the Coomassie Brilliant Blue method (r = 0.944; p less than 0.001) but less well with the Ponceau S (r = 0.895; p less than 0.001) or biuret-trichloroacetic acid (r = 0.874; p less than 0.001) methods. For urines with normal electrophoretic protein patterns, the imprecise biuret-trichloroacetic acid method (cv = 18.5%) gave the greatest number of false high results (23 in 36 urines) as assessed by electrophoresis. False low results were common in low relative molecular mass (Mr) proteinuria, especially with the biuret-tricholoroacetic acid and Ponceau S methods. High Mr proteinuria rarely caused false low results. Discrepancies between methods appear to have resulted from incomplete precipitation of low Mr protein by trichloroacetic acid.

Renal function and electrolyte levels in hyperthyroidism: urinary protein excretion and the plasma concentrations of urea, creatinine, uric acid, hydrogen ion and electrolytes.

In order to help clarify the effects of hyperthyroidism on renal function and electrolyte metabolism, we measured the venous plasma concentrations of urea, creatinine, urate, hydrogen ion and electrolytes, and the urinary concentrations of total protein, albumin, retinol-binding protein, N-acetyl-beta-D-glucosaminidase activity, and creatinine in patients when hyperthyroid and again after they had been euthyroid for at least 4 months. Significant (P less than 0.05) decreases in the mean plasma concentrations of urate and chloride and significant increases in creatinine, total CO2 and hydrogen ion mean concentrations were observed when the patients became euthyroid. The mean concentrations of sodium, potassium and urea did not change significantly. The values of the ratios total protein/creatinine, albumin/creatinine, N-acetylglucosaminidase/creatinine and retinol-binding protein/creatinine were all significantly (P less than 0.05) elevated in random urine specimens obtained from hyperthyroid patients as compared to the values when euthyroid. Mild proteinuria occurs in most thyrotoxic patients which does not appear to be due predominantly to either glomerular or tubular renal injury. The changes in plasma analytes that were observed may be attributed to increases in glomerular filtration rate and tissue nucleic acid turnover and a tendency to respiratory alkalosis in the hyperthyroid patients.

Effects of sodium dodecylsulphate, dye concentration and paraprotein on coomassie blue dye-binding assays for protein in urine.

Various Coomassie Blue reagents, containing either increased dye concentration or added sodium dodecylsulphate, were compared with a biuret method for the assay of total protein in urine. When immunoglobulin free light chain protein or immunoglobulin paraprotein were present, results from the Coomassie Blue methods were up to 50% lower than with the biuret method; increased dye concentration did not improve comparability substantially, but the addition of sodium dodecylsulphate reduced the bias to about 20%. When neither free light chain protein nor immunoglobulin paraprotein was present, results from the Coomassie Blue methods were only about 30% lower. The addition of sodium dodecylsulphate reduced this bias to 10%. Correlations between the biuret and the Coomassie Blue method were best when the Coomassie Blue reagent contained 40 mg/L sodium dodecylsulphate (r better than 0.98 in all groups; p less than 0.001).

Mitochondrial creatine kinase in cancer patients.

We have developed a quantitative immunoassisted enzyme assay to screen for creatine kinase isoenzymes BB (CK-BB) and mitochondrial (CK-m) using commercial antibodies and reagents. Presence of CK-m activity was subsequently confirmed by electrophoretic separation of samples with elevated values. A prospective clinical trial was undertaken in 117 subjects: Normal (30), cirrhosis patients (30), myocardial infarction patients (30), and untreated oncology patients with metastatic malignancy (27). In 12 patients with malignancy CK-m activities were elevated; all had adenocarcinomas. No significant activity was detected in patients with other malignancies. CK-m positive tumour patients had a significantly higher mortality rate, and in two instances death was preceded by a sudden rise in CK-m activity. We suggest CK-m is a marker of adenocarcinoma and its presence in serum signifies increased mortality.