Accuracy of the spot urinary microalbumin:creatinine ratio and visual dipsticks in hypertensive pregnant women

Abstract 

Objectives

New developments in proteinuria assessment have included the use of spot urinary microalbumin to creatinine ratio measurements. This study determines the accuracy of spot urinary microalbumin to creatinine ratio dipsticks and conventional visual dipsticks compared to the 24h urinary protein (gold standard) to detect significant proteinuria in hypertensive pregnant women.

Study design

163 women presenting with pregnancy hypertension were recruited from antenatal clinics. On admission each participant had a spot urine sample tested using a semi-quantitative visual dipstick and a spot midstream urine sample collected and analysed using the semi-quantitative urinary microalbumin to creatinine ratio dipsticks read instrumentally on the Clinitek^® 50 urine chemistry analyser. A 24h urinary protein estimation was then performed. The results of the urinary microalbumin to creatinine ratio dipsticks and the conventional visual dipsticks were compared to the 24h urine protein. A urinary microalbumin to creatinine ratio of ≥300mg/g (1+ to 4+ on urine dipsticks) was considered a positive result ≥0.3g/24h was considered significant proteinuria.

Results

The visual dipstick had a sensitivity of 51% (95% CI [0.41–0.61]) and specificity of 91% (95% CI [0.81–0.96]). The PPV and NPV was 89% (95% CI [0.77–0.95]) and 58% (95% CI [0.48–0.67]), respectively. The urinary microalbumin to creatinine ratio dipsticks had a sensitivity of 63% (95% CI [0.52–0.72]) and specificity of 81% (95% CI [0.70–0.89]). The PPV was 82% (95% CI [0.71–0.90]) and NPV was 62% (95% CI [0.51–0.71]).

Conclusion

Neither the visual dipstick nor the urinary microalbumin to creatinine ratio dipstick read on the Clinitek^® 50 system is accurate when compared to the total 24h urinary protein. Differences between the urinary microalbumin to creatinine ratio and 24h total urinary protein may be due to the variation in the albumin fraction of the total urinary protein of pre-eclampsia, technical problems with imprecision of the assay technique, and clinical causes of false positives and negatives. The improved sensitivity of the automated urinary microalbumin to creatinine ratio dipstick over the visual dipstick suggests it may be a suitable substitute for the visual dipstick in clinical practice.

Keywords: Accuracy of spot urinary microalbumin, Creatinine ratio, Visual dipsticks, Hypertensive pregnant women