Abstract: Diagnostic Accuracy Study of Urine Dipstick in Relation to 24-Hour Measurement as a Screening Tool for Proteinuria in Lupus Nephritis

Diagnostic Accuracy Study of Urine Dipstick in Relation to 24-Hour Measurement as a Screening Tool for Proteinuria in Lupus Nephritis

MARK J. SIEDNER, ALLAN C. GELBER, BRAD H. ROVIN, ALISON M. McKINLEY, LISA CHRISTOPHER-STINE, BRAD ASTOR, MICHELLE PETRI, and DEREK M. FINE

ABSTRACT.

Objective. Early detection of renal involvement in lupus prevents poor outcomes. Although published guidelines recommend urine dipstick as an appropriate screening test and evidence suggests a majority of American rheumatologists use dipstick to screen for proteinuria, the performance of this diagnostic approach in lupus has not been reported. We examined the validity of qualitative urine dipstick versus quantitative 24-hour measurement to accurately detect proteinuria, including low-level proteinuria.

Methods. We performed a diagnostic accuracy study using paired samples from the Johns Hopkins University School of Medicine and the Ohio State University School of Medicine lupus cohorts. All qualitative urine dipstick values were obtained within 1 day of a 24-hour urine collection.

Results. We analyzed the performance of 3 urine dipstick assays to detect proteinuria compared to 24-hour protein/creatinine ratios, using 2224 dipstick measures from 296 patients. The sensitivity of a ≥ 1+ dipstick result to detect quantitative proteinuria (≥ 0.50 g protein/g creatinine) was 82.7% for the Clinitek, 97.7% for the Atlas, and 85.5% for the Bayer assay. The corresponding sensitivity to detect low-level proteinuria, (0.50–0.99 g protein/g creatinine) was 63.1%, 96.4%, and 80.7%, respectively. The specificity to correctly exclude proteinuria (< 0.50 g protein/g creatinine) with negative/trace results was 86.1%, 62.2%, and 59.4%. There was considerable variability in the range of protein/creatinine ratios detected at each dipstick level of proteinuria.

Conclusion. Urine dipsticks demonstrate substantial variability and often poor validity to accurately detect proteinuria at quantitative levels; this warrants further diagnostic evaluation. Clinicians should consider quantified proteinuria assays as a more accurate screening tool in the diagnostic evaluation of lupus nephritis. (First Release Dec 15 2007; J Rheumatol 2008;35:84-90)

Key Indexing Terms:

SYSTEMIC LUPUS ERYTHEMATOSUS
NEPHRITIS
DIAGNOSTIC CRITERIA
PROTEINURIA

From the Columbia University College of Physicians and Surgeons, New York, New York; Johns Hopkins University School of Medicine, Baltimore, Maryland; The Ohio State University School of Medicine, Columbus, Ohio; and Johns Hopkins University Bloomberg School of Public Health, Baltimore, Maryland, USA.

Dr. Christopher-Stine was supported by an Arthritis Foundation Postdoctoral Fellowship Award. The Johns Hopkins Lupus Cohort is supported by the National Institutes of Health (AR43727) and the Johns Hopkins Clinical Research Center (M-1-RR00052). The Ohio State Lupus Cohort is supported by the National Institutes of Health (DK55546).

M.J. Siedner, MD, MPH, Columbia University College of Physicians and Surgeons; A.C. Gelber, MD, MPH, PhD, Associate Professor of Medicine and Epidemiology; L. Christopher-Stine, MD, MPH, Assistant Professor of Medicine; M. Petri, MD, MPH, Professor of Medicine; D.M. Fine, MD, Assistant Professor of Medicine, Johns Hopkins University School of Medicine; B.H. Rovin, MD, FACP, FASN, Professor of Medicine and Pathology; A.M. McKinley, BA, The Ohio State University School of Medicine; B. Astor, MPH, PhD, Assistant Professor of Epidemiology and Medicine, Johns Hopkins University Bloomberg School of Public Health.

Address reprint requests to Dr. D.M. Fine, Johns Hopkins University School of Medicine, 1830 East Monument Street, Suite 416, Baltimore, MD 21205. E-mail: dfine1@jhmi.edu

Accepted for publication September 10, 2007.