The role of automated urine particle flow cytometry in clinical practice

Urine particle flow cytometers (UFC) have improved count precision and accu racy compared to visual microscopy and offer significant labor saving. The absence of an internationally recognized reference measurement procedure, h owever, is a serious drawback to their validation. Chamber counting by phas e contrast microscopy of supravitally-stained uncentrifuged urine is consid ered the best candidate for reference. The UF-100 (Sysmex Corporation, Japa n) identifies RBC, WBC, squamous epithelial cells, transitional epithelial and renal tubular cells (SRC), bacteria, hyaline and inclusional casts, yea st-like cells, crystals and spermatozoa, using argon laser flow cytometry. Evaluations have established acceptable linearity over useful working range s, with an imprecision that is consistently and significantly less than mic roscopy, and with negligible carry-over. Comparisons of UFC with chamber co unts, quantitative urine microscopy, sediment counts, test strips, bacteria l culture and urine density are reviewed. Clinical studies include diagnosi s and monitoring of urinary tract infection; localization of the sites of h ematuria; and diagnosis, monitoring and exclusion of renal disease. The mos t popular approach is to combine test strips with UFC for primary screening either always by both methods or by using test strips for analytes unrelat ed to particles analyzed by UFC. Expert systems now exist combining both te st modalities based on user definable decision rules. The implementation of such a strategy significantly reduces microscopy review and saves time and expense without diminishing clinical utility. (C) 2000 Elsevier Science B. V. All rights reserved.