[Urinary specific gravity--comparative measurements using reagent strips and refractometer in 340 morning urine...

Area of Science:

• Nephrology
• Clinical Chemistry
• Urinalysis

Background:

• Urine specific gravity (SG) reflects solute concentration and is vital for assessing hydration and interpreting urinalysis findings.
• Accurate SG measurement is crucial for managing nephrolithiasis and understanding proteinuria.
• Existing methods for SG measurement include refractometry, urometry, freezing-point depression, and reagent strips.

Purpose of the Study:

• To evaluate the accuracy of a new reagent strip for measuring urine specific gravity (SG).
• To compare the performance of the new reagent strip against refractometry, a standard method.
• To identify conditions where the reagent strip's SG measurements may deviate significantly.

Main Methods:

• A cohort of 340 non-selected outpatients provided morning urine samples.
• Urine specific gravity was measured using both a new reagent strip and refractometry.
• Results from the two methods were statistically correlated (Pearson correlation coefficient).

Main Results:

• A strong positive correlation (r = 0.913, p = 0.0001) was observed between the reagent strip and refractometry in 86.2% of samples.
• Deviations greater than +/- 5 SG units occurred in 13.8% of urines.
• Discrepancies were often associated with glucosuria, proteinuria, bacteriuria, or leukocyturia.
• Alkaline urine (pH > 7.0) required a +5 correction for reagent strip SG values.

Conclusions:

• The new reagent strip offers a reliable method for measuring urine SG in the majority of outpatient samples.
• The presence of glucosuria, proteinuria, bacteriuria, or leukocyturia can impact reagent strip accuracy.
• A correction factor is necessary for alkaline urine to ensure accurate SG readings with the reagent strip.