Automated cell count in body fluids: a review

Timepoint of aspiration can impact diagnostic of PJI - synovial fluid analyses exhibit a high intraindividual variation in periprosthetic joint infections of the knee

BACKGROUND

Synovial leukocyte cell count (LC) and polymorphonuclear percentage (PMN%) are key parameters in the diagnostic workup of periprosthetic joint infection (PJI). Despite ongoing debates regarding optimal thresholds-particularly for reliably excluding low-grade infections-no study has investigated potential confounders such as intra-individual, time-dependent variability of LC and PMN% in patients with PJI following total knee arthroplasty (TKA).

METHODS

We conducted a retrospective, double-centre study using prospectively collected data from 35 consecutive patients with confirmed knee PJI, each of whom underwent two joint aspirations at different time points (t1 and t2; mean interval 33 ± 31 days, range 0-111 days; total 70 samples). We analysed absolute and percentage changes in LC and PMN% between t1 and t2 and identified the number of "false-negative" results potentially caused by this variability. A subset analysis was performed on cases exhibiting more than 20% variability to minimize methodological bias. Additionally, we compared LC and PMN% levels between infections caused by low- vs. high-virulence pathogens.

RESULTS

Mean LC among all samples was 19.969 n/µl ± 27.035 n/µl [300-135.000 n/µl], mean PMN% was 65%±28% [6-97%]. Seven (20%) of the LC results and four (11%) of the PMN% results exhibited discrepant values, either falling below or exceeding the threshold depending on the timepoint of aspiration. Regarding the time-dependent variability, there was a trend to higher percentual change for LC compared to PMN% (58% ± vs. 11%; p = 0.062). Synovial analyses of low-virulent bacteria showed significantly decreased overall LC- and PMN%-values compared to high virulent pathogen associated PJI (p < 0.001).

CONCLUSION

LC values exhibit significant intra-individual variability of up to 58% over time, which could lead to false-negative exclusion of PJI in up to 20% of cases if only a single aspiration were performed. In contrast, PMN% is less affected by timing, showing a variability of just 11%. Notably, in PJI caused by low-virulence pathogens, both LC and PMN% show approximately 80% variability, whereas PMN% variability in high-virulence infections is only 22%. LC, in particular, demonstrates a high degree of independent variability. These findings suggest that synovial LC-especially-is less reliable diagnostically than previously assumed. PMN%, on the other hand, appears to be less influenced by timing and pathogen virulence, and may therefore be the more robust parameter. In addition to timing, future research should explore other potential confounders that may impact the diagnostic reliability of both LC and PMN%.

LEVEL OF EVIDENCE

III.

Utility of the combination of high fluorescence cells and tumor markers for the diagnosis of malignant pleural effusions

BACKGROUND

New diagnostic tools have emerged to assist the traditional diagnosis of malignant pleural effusion (MPE), such as high fluorescence cells (HFc) and tumor markers (TMs), determined by clinical laboratory automated pleural fluid workup. This study aimed to evaluate the diagnostic ability of the combination of HFc and TMs for diagnosing MPE.

METHODS

We recruited hospitalized patients with pleural effusion at Parc Taulí University Hospital. We collected and analyzed pleural fluid and serum samples in the clinical laboratory, and we sent a sample of pleural fluid to the Pathology Department for cytology workup. We determined the pleural fluid cell count by Sysmex XN-10 and assessed TMs (CEA, CA19.9, and CA15.3) using the ECLIA Cobas e801 Roche in both pleural fluid and serum samples. We established the final MPE diagnosis based on positive cytology and/or positive pleural biopsy. We classified patients based on these final diagnoses and conducted a comparison between variables, along with multivariate logistic regression.

RESULTS

The study included 316 pleural effusions from 221 patients recruited. Multivariate logistic regression indicated the most significant predictor variables for MPE were CA15.3 in serum, CEA ratio, and HFc. We calculated two different models: one excluding HFc and one including it, with the latter displaying superior diagnostic ability (area under the curve 0.91). This model could identify 100 % of MPE cases with 30 % specificity at low cut-offs, and higher values could help identify 60 % of MPE cases with 100 % specificity.

CONCLUSIONS

Per our findings, this model has high diagnostic performance and could serve as a swift, automated, dependable, non-invasive tool for MPE detection.

Performance Assessment of Sysmex DI-60: Is Digital Morphology Analyzer Reliable for White Blood Cell Differentials in Body Fluids?

BACKGROUND

Few studies have evaluated digital morphology (DM) analyzers on body fluids (BF). We evaluated the performance of a DM analyzer, Sysmex DI-60 (Sysmex, Kobe, Japan) for white blood cell (WBC) differentials in BF samples.

METHODS

In five BF samples (two pleural fluids and three ascites) containing a single, dominant cell type (>80%, neutrophils, lymphocytes, macrophages, abnormal lymphocytes, and malignant cells in each sample), we evaluated the precision of the DI-60 and compared the WBC differentials and turnaround times (TAT) between DI-60 and manual counting.

RESULTS

The precision of the DI-60 pre-classification and verification was excellent (%CV, 0.01-3.16%). After verification, the DI-60 showed high sensitivity, specificity, and efficiency (ranges: 90.8-98.1%, 96.8-97.9%, and 92.5-98.0%, respectively) for the dominant cell types in neutrophil- and lymphocyte-dominant samples. For all samples, the DI-60 and manual counting showed high correlations for major cell types (neutrophils, lymphocytes, macrophages, and others, r = 0.72 to 0.94) after verification. The agreement between the pre-classification and verification of the DI-60 was strong in the neutrophil-dominant sample (κ = 0.81). The DI-60 showed a significantly longer TAT (min: s) than manual counting for all samples (median TAT/slide: 6:28 vs. 1:53, p < 0.0001), with remarkable differences in abnormal lymphocyte- and malignant cell-dominant samples (21:05 vs. 2:06; 12:34 vs. 2:25).

CONCLUSIONS

The DI-60 may provide reliable data in neutrophil- and lymphocyte-dominant BF samples. However, it may require longer times and higher workloads for WBC differentials especially in BF samples containing atypical cells. Further improvement would be needed before applying DM analyzers for routine clinical practice in BF analysis.

i-scope: A Compact automated fluorescence microscope for cell counting applications in low resource settings

Fluorescence microscopy has widespread applications across biological sciences. It has been routinely used for cell counting, which provides a preliminary diagnostic test for many infectious diseases. Conventional fluorescence microscopes are bulky, expensive, time-intensive and laborious. They often require trained operators to acquire and analyze data. We report a compact automated digital fluorescence microscopy system, i-scope, for cell counting applications. The i-scope employs a total internal reflection fluorescence (TIRF) mode of sample illumination, along with a brightfield mode. It has a magnification of 30X, an optical resolution of ~0.2 µm/pixel and offers sample scanning over 20 mm x 20 mm. A custom-written program enables automated image acquisition and analysis, thereby enhancing ease of operation. It has a compact form-factor and has been developed into a standalone system with a processing unit, screen, and other accessories to offer a portable and economic point-of-care diagnostic solution in low-resource settings. We analysed the performance of the i-scope for milk somatic cell enumeration and benchmarked it against that of a conventional fluorescence microscope.

Serous body fluid evaluation using the new automated haematology analyser Mindray BC-6800Plus

OBJECTIVES

Cellular analysis of body fluids (BF) has clinical relevance in several medical conditions. The objective of this study is twofold: (1) evaluate the analytical performance of the BF mode of Mindray BC-6800 Plus compared to manual counts under microscopy and (2) analyse if the high-fluorescent cell counts provided by the analyser (HF-BF) are useful to detect malignancy.

METHODS

A total of 285 BF was analysed: 250 corresponding to patients without neoplasia and 35 to patients with malignant diseases. Manual differential counts were performed in BF with ≥250 cells/μL. Percentages and absolute counts were obtained on the BC-6800Plus for total nucleated cells (TC-BF), mononuclear, polymorphonuclear and HF-BF. Statistical analysis was performed using Mann-Whitney U-test, Spearman's correlation, Passing-Bablok regression, Bland-Altman graph and ROC curve.

RESULTS

To compare manual and automatic total cell counts, samples were divided in three groups: <250, 250-1,000 and >1,000 cells/μL. Correlation was good in all cases (r=0.72, 0.73 and 0.92, respectively) without significant differences between both methods (p=0.65, 0.39 and 0.30, respectively). The concordance between methods showed values of 90%. Considering malignant samples, median HF-BF values showed significant higher values (102 cells/μL) with respect to non-malignant (4 cells/μL) (p<0.001). The cut-off value of 8.5 HF-BF/μL was able to discriminate samples containing malignant cells showing sensitivity and specificity values of 89 and 71%, respectively. Considering both, HF-BF and TC-BF values, sensitivity and specificity values were 100 and 53%, respectively.

CONCLUSIONS

This study reveals that the Mindray BC-6800Plus offers an accurate and acceptable performance, showing results consistent with the manual method. It is recommended to consider both HF-BF and TC-BF values for the screening of the microscopic evaluation to ensure the detection of all malignant samples.

Optimization of the Transwell® assay for the analysis of neutrophil chemotaxis using flow cytometry to refine the clinical investigation of immunodeficient patients

Chemotaxis is the directed movement of neutrophils towards an infected site. This physiological process can be reproduced using a modified Boyden chamber, such as the Transwell® support. Different techniques can be used to count neutrophils after migration to the lower chamber of the holder. The present study supports the use of an optimized Transwell® assay coupled with a flow cytometry-based method (Sysmex XN-9000) to detect chemotaxis abnormalities. A reference interval of neutrophil's chemotaxis was determined as part of this work. A first step involves the extraction of neutrophils from whole blood. The migration of neutrophils from the upper to the lower support chamber is subsequently directed by a chemoattractant gradient using N-formyl-l-Methionyl-l-Leucyl-l-Phenylalanine (fMLP). Neutrophils collected in the lower chamber are finally counted by flow cytometry. The original protocol was optimized through the comparison of different parameters. The use of Polymorphprep®, in the extraction of neutrophils, showed an improvement of the neutrophils yield of 1.65 times (57.5% of recovery) compared to the extraction using the Ficoll-Hypaque® gradient. A solution containing 5% of Bovin Serum Albumin (BSA) was used to suspend the extracted neutrophils, stabilize their viability and preserve their integrity. The mechanical agitation of the Transwell® permeable supports during migration did not show an increase in neutrophil yield. A migration time of 1 h 30 was identified as the best time for collecting the largest number of neutrophils after migration. Finally, we demonstrated that scraping the bottom of the well after migration improved neutrophil collection from the lower chamber by 1.9-fold compared to a non-scraping method. In conclusion, our results support the use of Polymorphprep® and a 5% BSA solution in the suspension, without agitation of the medium. An incubation time of 1 h 30 was identified as optimal for neutrophil migration through the chamber. Scraping the bottom after neutrophil migration improved neutrophil collection yield. Normal adult values were obtained with directed migration equal to 32.4% ±13.41% on 15 men and 18 women.

What is the future of electrical impedance spectroscopy in flow cytometry?

More than 20 years ago, electrical impedance spectroscopy (EIS) was proposed as a potential characterization method for flow cytometry. As the setup is comparably simple and the method is label-free, EIS has attracted considerable interest from the research community as a potential alternative to standard optical methods, such as fluorescence-activated cell sorting (FACS). However, until today, FACS remains by and large the laboratory standard with highly developed capabilities and broad use in research and clinical settings. Nevertheless, can EIS still provide a complement or alternative to FACS in specific applications? In this Perspective, we will give an overview of the current state of the art of EIS in terms of technologies and capabilities. We will then describe recent advances in EIS-based flow cytometry, compare the performance to that of FACS methods, and discuss potential prospects of EIS in flow cytometry.