Can total urinary protein measurements predict microalbuminuria?

Area of Science:

• Nephrology
• Diabetology
• Clinical Chemistry

Background:

• Microalbuminuria is an early indicator of diabetic nephropathy.
• Accurate prediction of microalbuminuria is crucial for timely intervention.
• Routine total urinary protein assays are widely available but their predictive value for microalbuminuria requires clarification.

Purpose of the Study:

• To evaluate the efficacy of routine total urinary protein determinations in predicting microalbuminuria in diabetic patients.
• To compare the performance of different total urinary protein measurement methods against radioimmunoassay (RIA) for albumin.

Main Methods:

• Studied 61 diabetic patients with negative or one positive dipstick protein test.
• Measured total urinary protein using Biorad dye-binding method in undialyzed urine (UND), dialyzed urine (DIAL), and separated albumin and globulin (A + G).
• Compared results with albumin measurements obtained by radioimmunoassay (RIA).

Main Results:

• Total urinary protein measurements were higher with A + G (43%) and UND (22%) compared to DIAL.
• Microalbuminuria showed moderate to good correlation with all methods (r=0.81 for UND, r=0.87 for DIAL, r=0.91 for A + G).
• The A + G method had the highest negative predictive value (91%), while DIAL had the highest positive predictive value (90%).

Conclusions:

• No single method reliably predicted microalbuminuria.
• The A + G method, despite more false positives, is most suitable for screening due to the lowest false negative rate.
• Physicians should be aware of the limitations of routine undialyzed urine (UND) protein measurements.