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Can the Urine Dipstick Test Reduce the Need for Microscopy for Assessment of Systemic Lupus Erythematosus Disease Activity?
REBECCA WING-YAN CHAN, KAI-MING CHOW, LAI-SHAN TAM, EDMUND KWOK-MING LI, SIU MAN WONG, PHILIP KAM-TAO LI, and CHEUK-CHUN SZETO
ABSTRACT.
Methods. We studied 269 urine samples from 259 SLE patients with Albustix™ and Hemastix™ reagent strips. The results were compared to concomitant microscopic examination of urinary sediment. Results. When trace red blood cell was defined as the cutoff, the sensitivity, specificity, and negative predictive value (NPV) of the Hemastix urine test were 0.98, 0.53, and 0.99, respectively, for hematuria; 0.82, 0.47, and 0.90, respectively, for the presence of pyuria; and 0.91, 0.44, and 0.98, respectively, for the presence of casts by microscopic examination. When proteinuria of 1+ was defined as the cutoff, the sensitivity, specificity, and NPV of the Albustix test were 1.00, 0.46, and 0.99, respectively, for urinary casts; and 0.82, 0.49, and 0.90, respectively, for the presence of pyuria. When both Albustix and Hemastix were applied as screening test, urine microscopy could be reduced by 27%; however, 8% of cases with normal Albustix and Hemastix tests had at least one abnormality on urine microscopy examination. Conclusion. In patients with SLE, a combination of Albustix and Hemastix urine tests showed reasonable sensitivity to detect abnormalities in urine sediment. Based on these results, routine urine microscopy can be limited to SLE patients with abnormal Albustix or Hemastix tests. Rarer causes of abnormal renal function in lupus, such as tubulointerstitial nephritis or drug induced interstitial nephritis, would be manifested by pyuria and therefore would not necessarily be detected by changes in the blood and protein detectors on the urine dipstick. (J Rheumatol 2005;32:828-31) Key Indexing Terms:
SYSTEMIC LUPUS ERYTHEMATOSUS
From the Department of Medicine and Therapeutics, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong, China. Supported in part by Chinese University of Hong Kong research accounts 6900972 and 6900570. R.W-Y. Chan, BSc(Hons), Research Assistant; K-M. Chow, MBChB, MRCP(UK), Fellow; L-S. Tam, MBChB, MRCP(UK), Fellow; E.K-M. Li, MD, FRCPC, Associate Professor; S-M. Wong, MBBS, MRCP(UK), Fellow; P.K-T. Li, MD, FRCP, Consultant; C-C. Szeto, MD, FRCP(Edin), Associate Professor. Address reprint requests to Dr. C.C. Szeto, Department of Medicine and Therapeutics, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong. E-mail: ccszeto@cuhk.edu.hk Accepted for publication December 20, 2004. |