Dipstick measurements of urine specific gravity are unreliable.
OBJECTIVE
To evaluate the reliability of dipstick measurements of urine specific gravity (U-SG).


METHODS
Fresh urine specimens were tested for urine pH and osmolality (U-pH, U-Osm) by a pH meter and an osmometer, and for U-SG by three different methods (refractometry, automatic readout of a dipstick (Clinitek-50), and (visual) change of colour of the dipstick).


RESULTS
The correlations between the visual U-SG dipstick measurements and U-SG determined by a refractometer and the comparison of Clinitek((R))-50 dipstick U-SG measurements with U-Osm were less than optimal, showing very wide scatter of values. Only the U-SG refractometer values and U-Osm had a good linear correlation. The tested dipstick was unreliable for the bedside determination of U-SG, even after correction for U-pH, as recommended by the manufacturer.


CONCLUSIONS
Among the bedside determinations, only refractometry gives reliable U-SG results. Dipstick U-SG measurements should be abandoned.
de Buys Roessingh
A S
AS
Renal Unit, Department of Paediatrics, University Medical Centre (CHUV), CH-1011 Lausanne, Switzerland.
Drukker
A
A
Guignard
J P
JP
D006801:Humans; D006863:Hydrogen-Ion Concentration; D009994:Osmolar Concentration; D019095:Point-of-Care Systems / Q000592:standards; D011933:Reagent Kits, Diagnostic / Q000592:standards*; D012031:Refractometry; D015203:Reproducibility of Results; D013046:Specific Gravity; D016482:Urinalysis / Q000379:methods*
D011933:Reagent Kits, Diagnostic