Urine specific gravity measurement: reagent strip versus refractometer.
OBJECTIVE
To compare the results of urinalysis screenings for specific gravity (SG) using the reagent strip and the refractometer.


METHODS
United Hospital, Grand Forks, North Dakota.


METHODS
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).


METHODS
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.


CONCLUSIONS
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.
Department of Microbiology and Immunology, University of North Dakota, Grand Forks, USA.
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Brandon
D006801:Humans; D011934:Reagent Strips; D012031:Refractometry; D013046:Specific Gravity; D016482:Urinalysis / Q000379:methods*