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Urine specific gravity measurement: reagent strip versus refractometer
1Department of Microbiology and Immunology, University of North Dakota, Grand Forks, USA.
Objective:
To compare the results of urinalysis screenings for specific gravity (SG) using the reagent strip and the refractometer.
Setting:
United Hospital, Grand Forks, North Dakota.
Practice Description:
United Hospital is a 384-bed teaching hospital. PRODUCT COMPARISON: The Ames Multistix 10 SG reagent strip (Miles, Inc., Elkhart, IN 46515) was compared with the TS Meter (Leica, Inc., Deerfield, IL 60015).
Main Outcome Measurement:
The degree of correlation between the results produced by each method.
Results:
The percentage of difference between the means of the direct strip readings and the refractometer readings was 9.68%. The percentage of difference between the means of the adjusted strip readings and the refractometer readings was 22.58%, which was significantly different. When the direct strip readings and the refractometer readings were plotted together on a graph, the points were widely scattered; this fact, and a correlation coefficient of 0.725, suggest that random error occurred in both methods. Analysis of the slope and intercept of the correlation indicated systematic error.
Conclusion:
The reagent strip method of measuring SG is accurate only in a narrow range of "average" values, and should not be used as the basis for medical diagnoses.