Evaluation of automated synovial fluid total cell count and percent polymorphonuclear leukocytes on a Sysmex XN-1000 analyzer for identifying patients at risk of septic arthritis

Abstract

Background: Total cell counts (TC-BF) and percent polymorphonuclear cells (%PMN) of synovial fluid (SF) aspirates provide important cues for the timely diagnosis and management of septic arthritis. To facilitate faster turnaround time, we compared automated to manual TC-BF and differential counts in order to identify reporting cut-offs for automated TC-BF and %PMN that would allow release of automated results concordant with manual counts and differentials.

Methods: Automated TC-BF and %PMN counts of a non-validated analyzer (Analyzer-B in STAT laboratory) were compared to a validated analyzer (Analyzer-A) and manual TC-BF counts and cytospin differentials. Concordance and %differences of Analyzer-B versus Analyzer-A and manual counts were assessed by linear regression analysis and Bland-Altman comparison.

Results: Overall, automated and manual counts displayed good correlation. A majority of samples demonstrated unacceptable (>20%) differences between automated and manual counts at lower TC-BF (<10,000 cells/μl) and %PMN (<60%).

Conclusions: Based on good overall correlation and fewer samples with unacceptable (>20%) differences between automated and manual counts, we adopted TC-BF > 10,000 cells/μl and %PMN > 60% as cutoffs for reporting automated counts. These cutoffs minimize differences between automated and manual cell counts and differentials and would allow rapid automated reporting in the vast majority of septic arthritis cases.

Keywords: Septic arthritis; Synovial fluids; Sysmex XN-1000.