The role of automated urine particle flow cytometry in clinical practice.

Urine particle flow cytometers (UFC) have improved count precision and accuracy compared to visual microscopy and offer significant labor saving. The absence of an internationally recognized reference measurement procedure, however, is a serious drawback to their validation. Chamber counting by phase contrast microscopy of supravitally-stained uncentrifuged urine is considered the best candidate for reference. The UF-100 (Sysmex Corporation, Japan) identifies RBC, WBC, squamous epithelial cells, transitional epithelial and renal tubular cells (SRC), bacteria, hyaline and inclusional casts, yeast-like cells, crystals and spermatozoa, using argon laser flow cytometry. Evaluations have established acceptable linearity over useful working ranges, with an imprecision that is consistently and significantly less than microscopy, and with negligible carry-over. Comparisons of UFC with chamber counts, quantitative urine microscopy, sediment counts, test strips, bacterial culture and urine density are reviewed. Clinical studies include diagnosis and monitoring of urinary tract infection; localization of the sites of hematuria; and diagnosis, monitoring and exclusion of renal disease. The most popular approach is to combine test strips with UFC for primary screening either always by both methods or by using test strips for analytes unrelated to particles analyzed by UFC. Expert systems now exist combining both test 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.

Towards European urinalysis guidelines. Introduction of a project under European Confederation of Laboratory Medicine.

Improved standardized performance is needed because urinalysis continues to be one of the most frequently requested laboratory tests. Since 1997, the European Confederation of Laboratory Medicine (ECLM) has been supporting an interdisciplinary project aiming to produce European urinalysis guidelines. More than seventy clinical chemists, microbiologists and ward-based clinicians, as well as representatives of manufacturers are taking part. These guidelines aim to improve the quality and consistency of chemical urinalysis, particle counting and bacterial culture by suggesting optimal investigative processes that could be applied in Europe. The approach is based on medical needs for urinalysis. The importance of the pre-analytical stage for total quality is stressed by detailed illustrative advice for specimen collection. Attention is also given to emerging automated technology. For cost containment reasons, both optimum (ideal) procedures and minimum analytical approaches are suggested. Since urinalysis mostly lacks genuine reference methods (primary reference measurement procedures; Level 4), a novel classification of the methods is proposed: comparison measurement procedures (Level 3), quantitative routine procedures (Level 2), and ordinal scale examinations (Level 1). Stepwise strategies are suggested to save costs, applying different rules for general and specific patient populations. New analytical quality specifications have been created. After a consultation period, the final written text will be published in full as a separate document.

Evaluation of plasma cystatin C as a marker for glomerular filtration rate in patients with type 2 diabetes.

AIM: To evaluate plasma cystatin C as a marker of the glomerular filtration rate in patients with type 2 diabetes and their age and sex-matched controls. MATERIALS AND METHODS: Forty-seven patients with one decade of type 2 diabetes and 51 non-diabetic control subjects were studied. Plasma cystatin C was measured by particle-enhanced turbidimetric immunoassay in a new application for the Hitachi 704 analyzer. For comparison, plasma creatinine and creatinine clearance were measured. The plasma clearance of 51Cr-EDTA by the single injection method was utilized as reference. RESULTS: In patients with type 2 diabetes the correlation coefficient between plasma cystatin C and the plasma clearance of 51Cr-EDTA was 0.774 (Spearman's coefficient) and that between plasma creatinine and the plasma clearance of 51Cr-EDTA was 0.556 (p = 0.001 for the difference). The correlation between creatinine clearance and the plasma clearance of 51Cr-EDTA was 0.411. In receiver operating characteristic (ROC) curve analysis the diagnostic accuracy of plasma cystatin C was significantly better than that of plasma creatinine (p = 0.047) or creatinine clearance (p = 0.001). The best diagnostic efficiency (98%) for cystatin C was obtained when the cut-off limit was set at 1.32 mg/l. In the control group the correlation coefficients were: between cystatin C and the plasma clearance of 51Cr-EDTA 0.627, between creatinine and the plasma clearance of 51Cr-EDTA 0.466 and between creatinine clearance and the plasma clearance of 51Cr-EDTA 0.416. The area under the ROC plot curve of cystatin C was also greatest in the control group, but the diagnostic accuracy of cystatin C was marginally better than that of either plasma creatinine (p = 0.05) or creatinine clearance (p = 0.08). Among the control subjects various non-renal causes may have interfered with cystatin C concentrations reducing the correlations. CONCLUSIONS: Cystatin C measurement is a more sensitive and specific test for GFR in patients with type 2 diabetes than plasma creatinine or its clearance, when GFR is normal or only slightly reduced. If an elevated cystatin C concentration is found, non-renal factors have to be excluded. The turbidimetric application described here can easily be applied for most clinical chemistry analyzers and is therefore useful in daily clinical practice.

Evaluation of Sysmex UF-100 urine flow cytometer vs chamber counting of supravitally stained specimens and conventional bacterial cultures.

We evaluated the Sysmex UF-100 urine flow cytometer (TOA Medical Electronics, Kobe, Japan) with 269 uncentrifuged urine specimens by comparing it with Sternheimer staining and particle counting in 1-microL disposable chambers with both brightfield and phase-contrast microscopy (the reference method). Results of routine test strip analysis, sediment microscopy (182 specimens), and bacterial culture (204 specimens) were also available. Detection of urinary WBCs and RBCs was highly reliable with the UF-100 compared with manual chamber counting (r = .98 and .88, respectively). Identification of bacteria was equal to that with visual microscopy of uncentrifuged specimens; sensitivity was 55%, and specificity 90%, compared with bacterial cultures at a cutoff of > 10(3) colony-forming units per milliliter. Renal damage was difficult to evaluate even with manual methods because of the low counts of renal tubular cells and casts; with standard manual Sternheimer-stained sediment analysis, sensitivity was 65% to 69% and specificity 66% to 91%, compared with the uncentrifuged chamber method at a cutoff of 3 and 10 particles per microliter, respectively. Renal damage was demonstrated with the UF-100 with a sensitivity of 26% to 69% and specificity 92% to 94%, compared with chamber counts. Automated urinalysis with the UF-100 urine flow cytometer offers considerable savings in time and labor. When high sensitivity is needed, visual microscopic review should be performed to detect renal disease.

Microalbuminuria. Invalidity of simple concentration-based screening tests for early nephropathy due to urinary volumes of diabetic patients.

OBJECTIVE: To evaluate the possibility of replacing quantitative albumin excretion rate (AER) measurements with rapid screening tests for microalbuminuria. RESEARCH DESIGN AND METHODS: Dipstick-negative specimens from 363 consecutive insulin-dependent diabetes mellitus (IDDM) and 46 non-insulin-dependent diabetes mellitus (NIDDM) patients from primary-care and hospital clinics (11% inpatients) within the district of Turku University Hospital were studied. Albumin concentrations and 12-h nightly excretion rates (N-AER) were measured by nephelometry (sensitivity 2 mg/L). RESULTS: An increased N-AER (greater than 15 micrograms/min) was seen in 99 IDDM (27%) and 15 NIDDM (33%) patients. The median urinary volume was 900 ml/12 h, with a maximum of 3000 ml. At the level of 20 mg albumin/L, the sensitivity to detect elevated N-AER was 70% among IDDM patients and 60% among NIDDM patients. At a lower albumin concentration of 10 mg/L, the sensitivities were increased to 91 and 87% in IDDM and NIDDM patients, respectively, but the specificities were reduced to 77 and 71%, respectively. CONCLUSIONS: To evaluate incipient nephropathy, we recommend quantitative measurements of N-AER from timed urine collections only. Dipstick tests are either insensitive or nonspecific.