PP025. Urinary dipstick proteinuria testing – Does automated strip analysis offer an advantage over visual testing?

Abstract

The visual urinary test strip is widely accepted for screening for proteinuria in pregnancy, given the convenience of the method and its low cost. However, test strips are known to lack sensitivity and specificity. The 2010 NICE (National Institute for Health and Clinical Excellence) guidelines for management of pregnancy hypertension have recommended the use of an automated test strip reader to confirm proteinuria (http://nice.org.uk/CG107). Superior diagnostic test performance of an automated (vs. visual) method has been proposed based on reduced subjectivity. To compare the diagnostic test properties of automated vs. visual read urine dipstick testing for detection of a random protein:creatinine ratio (PrCr) of ⩾30mg/mmol. In this prospective cohort study, consecutive inpatients or outpatients (obstetric medicine and high-risk maternity clinics) were evaluated at a tertiary care facility. Random midstream urine samples (obtained as part of normal clinical care) were split into two aliquots. The first underwent a point-of-care testing for proteinuria using both visual (Multistix 10SG, Siemens Healthcare Diagnostics, Inc., Tarrytown NY) and automated (Chemstrip 10A, Roche Diagnostics, Laval QC) test strips, the latter read by an analyser (Urisys 1100®, Roche Diagnostics, Laval QC). The second aliquot was sent to the hospital laboratory for analysis of urinary protein using a pyrocatechol violet molybdate dye-binding method, and urinary creatinine using an enzymatic method, both on an automated analyser (Vitros® 5,1 FS or Vitros® 5600, Ortho-Clinical Diagnostics, Rochester NY); random PrCr ratios were calculated in the laboratory. Following exclusion of dilute samples with urinary creatinine concentration <3mM (given inflation of PrCr values in dilute urine by our method), diagnostic test properties were determined for visual and automated dipstick proteinuria testing (⩾1+) for detection of a random PrCr ⩾30mg/mmol. 160 women (81.9% outpatients) were screened at one/more antenatal visits, providing a total of 233 urine samples for analysis. Both visual and automated read urinary dipstick testing showed low sensitivity (56.0% and 53.9%, respectively). Positive likelihood ratios (LR+) and 95% CI were 15.0 [5.9,37.9] and 24.6 [7.6,79.6], respectively. Negative LR (LR-) were 0.46 [0.29,0.71] and 0.47 [0.31,0.72], respectively. Automated dipstick urinalysis is not more sensitive than visual read urinalysis for detection of proteinuria in a primarily outpatient setting in pregnancy. Both have excellent LR+ but only fair to poor LR- as previously recognised for visual dipstick testing. Performance of automated strip analysis testing may vary with the test strips and analyser used.