Establishment of a reference procedure to measure urine-formed elements and evaluation of an automated urine analyzer

Abstract

A standardized reference method is needed to accurately and precisely measure urine-formed elements (UFEs; red blood cells [RBCs], white blood cells [WBCs], and squamous epithelial cells [sECs]). We compared the results from a standard method with those from an automated analyzer. Trained technicians used standardized bright-field microscopy of fresh non-centrifuged urine samples, and disposable 1 µl chambers. Fifteen experienced technicians from 5 hospitals (3 per hospital) each performed 6 manual counts of 10 different native urine samples using a manual chamber and standard methods. The sEC counts were at least 50/µL, and the coefficient of variation (CV) was less than 14%; the RBC and WBC counts were at least 200/µL and the CVs were less than 7%. The same samples were also analyzed 6 times using automated analyzers. The means, CVs, and biases were determined. The median CVs for the manual measurements were 6.4% (WBCs), 6.6% (RBCs), and 12.7% (sECs). The CVs of the automated analyzer were 4.7% (WBCs), 5.6% (RBCs), and 9.2% (sECs). Biases between the automated and manual methods were −2.9% to 5.0%(WBCs), −0.8% to 8.8% (RBCs) and −2.8% to 9.4% (sECs). The count mean values and expanded uncertainties of these counts were (224.5 ± 15.0) cells/µL, (234.2 ± 16.2) cells/µL, and (61.5 ± 7.9) cells/µL, respectively. The standardized manual method for measuring UFEs had high precision and accuracy, making it a suitable reference method. Use of this reference method to calibrate an automated analyzer improved the accuracy of automated analysis.

Keywords:

• Urine formed elements
• reference method
• automated microscopy analyzer
• coefficient of variation
• bias

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This study was supported by Application of Clinical Characteristics in Capital (Z12110200510000), the National Natural Science Foundation of China (81501802 and 81672074), Beijing Municipal Administration of Hospitals Clinical Medicine Development of Special Funding Support (ZYLX201811) and 1351 Talent Training Plan (CYMY-2017-01 and CYXX-2017-01). The funding sources had no involvement in the study design; in the collection, analysis and interpretation of data; in the writing of the report; and in the decision to submit the article for publication.