Comparison of Urinary Total Proteins by Four Different Methods.

Area of Science:

• Clinical Chemistry
• Biochemical Analysis

Background:

• Accurate quantification of total proteins in human urine is crucial for diagnosing various kidney diseases.
• Existing methods for urine protein analysis lack comprehensive evaluation of their precision and bias.

Purpose of the Study:

• To compare the performance of four different methods for total urine protein quantification: pyrogallol red molybdate, sulfosalicylic acid, sulfosalicylic acid with sodium sulphate, and trichloroacetic acid.
• To assess the imprecision and bias of each method to determine the most reliable option.

Main Methods:

• Analysis of fresh urine samples from 36 patients using the four specified methods.
• Determination of imprecision through repeated analyses.
• Assessment of inaccuracy and bias using method comparison studies, including correlation plots, Bland and Altman analysis, and Passing and Bablok regression.

Main Results:

• The coefficient of variation ranged from 3.97% (sulfosalicylic acid with sodium sulphate) to 6.84% (sulfosalicylic acid).
• Bland and Altman analysis indicated varying biases between methods, with pyrogallol red molybdate showing biases of 5.8, 1.7, and -5.4 against sulfosalicylic acid, sulfosalicylic acid with sodium sulphate, and trichloroacetic acid, respectively.
• Passing and Bablok regression identified constant bias for pyrogallol red molybdate against turbidimetric methods and proportional bias with the trichloroacetic acid method.

Conclusions:

• The sulfosalicylic acid with sodium sulphate method exhibits superior precision and minimal bias compared to sulfosalicylic acid and trichloroacetic acid methods.
• This enhanced precision suggests the sulfosalicylic acid with sodium sulphate method is the preferred choice for routine total urine protein analysis.