Automated counting of white blood cells in synovial fluid

Laboratory workflow for optimizing leukocyte count and differential in synovial fluids on Sysmex XN-1000

INTRODUCTION

Falsely elevated synovial white blood cell (WBC) counts using automated hematology analyzers have been reported particularly in the setting of joint arthroplasty. We evaluated the implementation of a laboratory workflow based on Sysmex XN-1000-automated cell counting and scattergram interpretation.

METHODS

WBC and differential were measured for 76 synovial fluid samples (29 native joints and 47 with joint arthroplasties) with Sysmex XN-1000 and manual methods. All scattergrams were evaluated for possible incorrect WBC and/or differential according to our implemented workflow. A specific finding was the "banana-shape" scattergram, which indicates possible interferences. The European Bone & Joint Infection Society (EBJIS) criteria were applied to identify possible prosthetic joint infections (PJIs) in patients with joint arthroplasties.

RESULTS

Correlation between automated and manual WBC counts, calculated for samples with WBC count <50 000/μL, was higher for native joints (r = 0.938) compared with patients known with arthroplasty (r = 0.906). Scattergrams classified as OK showed overall a higher correlation compared with scattergrams, which were interpreted as NOT OK. "Banana-shape" scattergrams (n = 19) showed falsely elevated automated WBC count, and the patterns were mainly seen in prosthesis patients (17/19 [89%]). Six of 47 (13%) patients with joint arthroplasties were reclassified from "confirmed" to "unlikely" PJI according to the EBJIS criteria.

CONCLUSION

Our workflow based on scattergram interpretation resulted in accurate WBC counts in synovial fluid using automated/and or manual methods. It is important to identify the presence of "banana-shape" scattergrams to avoid overestimated automated WBC counts. Overall, automated synovial WBC count can be used, even for patients with arthroplasty, but after visual inspection of the scattergram to exclude possible interferences.

Update on the role of pathology and laboratory medicine in diagnosing periprosthetic infection

Technological and implant design advances have helped reduce the frequency of aseptic total joint arthroplasty failure, but periprosthetic joint infections (PJI) remain a clinical important problem with high patient morbidity. Misinterpreting PJI as aseptic mechanical loosening commonly leads to unsatisfactory revision arthroplasty, persistent infection, and poor long-term results. While there is no single "gold standard" diagnostic test for PJI, recent collaborative efforts by Orthopaedic and Infectious Disease Societies have developed algorithms for diagnosing PJI. However, the efficacy of individual tests as well as diagnostic thresholds are controversial. We review the recommended thresholds for commonly used screening tests as well as tissue histopathology and confirmatory tests to diagnose periprosthetic infection. We also update lesser-known laboratory tests, and we briefly summarize rapidly evolving molecular tests to diagnose periprosthetic infection. Pathologists hold a critical role in assisting with PJI diagnosis, maintaining laboratory test quality and interpreting test results. Collaboration between clinicians and pathologists is essential to provide optimal patient care and reduce the burden of PJI.

Development and evaluation of automated synovial fluid total cell count on an Iris iQ® 200 for identifying patients at risk of septic arthritis

Septic arthritis is a diagnostic emergency. The white blood cell (WBC) count, in synovial fluid (SF), can guide the diagnosis. From November 2021 to November 2022, we included 350 SF. The WBC count was performed with the Iris iQ® 200 compared with the manual method. Automated and manual counts displayed good correlation. However, a Bland Altman plot demonstrates a higher percentage difference at higher WBC counts. The use of Iris iQ® 200 for SF analysis enables a rapid and accurate assessment for WBC count. Its implementation would advantageously replace the long and tedious optical analysis in daily routine.

Utility of Diagnostic Tests Before Reimplantation in Patients Undergoing 2-Stage Revision Total Joint Arthroplasty: A Systematic Review and Meta-analysis

INTRODUCTION

Periprosthetic joint infection (PJI) is a devastating complication after total joint arthroplasty (TJA), with treatment failure occurring in 12% to 28% after 2-stage revision. It is vital to identify diagnostic tools indicative of persistent infection or treatment failure after 2-stage revision for PJI.

METHODS

The Cochrane Library, PubMed (MEDLINE), and EMBASE were searched for randomized controlled trials and comparative observational studies published before October 3, 2021, which evaluated the utility of serum/plasma biomarkers (erythrocyte sedimentation rate [ESR], C-reactive protein [CRP], interleukin-6 [IL-6], fibrinogen, D-dimer), synovial biomarkers (white blood cell [WBC] count, neutrophil percentage [PMN %], alpha-defensin [AD], leukocyte esterase [LE]), tissue frozen section, tissue culture, synovial fluid culture, or sonicated spacer fluid culture indicative of persistent infection before the second stage of 2-stage revision for PJI or treatment failure after 2-stage revision for PJI.

RESULTS

A total of 47 studies including 6,605 diagnostic tests among 3,781 2-stage revisions for PJI were analyzed. Among those cases, 723 (19.1%) experienced persistent infection or treatment failure. Synovial LE (sensitivity 0.25 [0.10-0.47], specificity 0.99 [0.93-1.00], positive likelihood ratio 14.0 [1.45-135.58]) and serum IL-6 (sensitivity 0.52 [0.33-0.70], specificity 0.92 [0.85-0.96], positive likelihood ratio 7.90 [0.86-72.61]) had the highest diagnostic accuracy. However, no biomarker was associated with a clinically useful negative likelihood ratio. In subgroup analysis, synovial PMN %, synovial fluid culture, serum ESR, and serum CRP had limited utility for detecting persistent infection before reimplantation (positive likelihood ratios ranging 2.33-3.74; negative likelihood ratios ranging 0.31-0.9) and no utility for predicting failure after the second stage of 2-stage revision.

CONCLUSIONS

Synovial WBC count, synovial PMN %, synovial fluid culture, serum ESR, and serum CRP have modest sensitivity and specificity for predicting persistent infection during the second stage of 2-stage revision, suggesting some combination of these diagnostic tests might be useful before reimplantation. No biomarker or culture accurately predicted treatment failure after reimplantation.

LEVEL OF EVIDENCE

Level III. See Instructions for Authors for a complete description of levels of evidence.

The Graphical Representation of Cell Count Representation: A New Procedure for the Diagnosis of Periprosthetic Joint Infections

Aim: This study was designed to answer the question whether a graphical representation increase the diagnostic value of automated leucocyte counting of the synovial fluid in the diagnosis of periprosthetic joint infections (PJI). Material and methods: Synovial aspirates from 322 patients (162 women, 160 men) with revisions of 192 total knee and 130 hip arthroplasties were analysed with microbiological cultivation, determination of cell counts and assay of the biomarker alpha-defensin (170 cases). In addition, microbiological and histological analysis of the periprosthetic tissue obtained during the revision surgery was carried out using the ICM classification and the histological classification of Morawietz and Krenn. The synovial aspirates were additionally analysed to produce dot plot representations (LMNE matrices) of the cells and particles in the aspirates using the hematology analyser ABX Pentra XL 80. Results: 112 patients (34.8%) had an infection according to the ICM criteria. When analysing the graphical LMNE matrices from synovia cell counting, four types could be differentiated: the type “wear particles” (I) in 28.3%, the type “infection” (II) in 24.8%, the “combined” type (III) in 15.5% and “indeterminate” type (IV) in 31.4%. There was a significant correlation between the graphical LMNE-types and the histological types of Morawietz and Krenn (p < 0.001 and Cramer test V value of 0.529). The addition of the LMNE-Matrix assessment increased the diagnostic value of the cell count and the cut-off value of the WBC count could be set lower by adding the LMNE-Matrix to the diagnostic procedure. Conclusion: The graphical representation of the cell count analysis of synovial aspirates is a new and helpful method for differentiating between real periprosthetic infections with an increased leukocyte count and false positive data resulting from wear particles. This new approach helps to increase the diagnostic value of cell count analysis in the diagnosis of PJI.

Assessment of the in vivo biofunctionality of a biomimetic hybrid scaffold for osteochondral tissue regeneration

Chondral and osteochondral lesions represent one of the most challenging problems in the orthopedic field, as these types of injuries lead to disability and worsened quality of life for patients and have an economic impact on the healthcare system. The aim of this in vivo study was to develop a new tissue engineering approach through a hybrid scaffold for osteochondral tissue regeneration made of porous polyurethane foam (PU) coated under vacuum with calcium phosphates (PU/VAC). Scaffold characterization showed a highly porous and interconnected structure. Human amniotic mesenchymal stromal cells (hAMSCs) were loaded into scaffolds using pectin (PECT) as a carrier. Osteochondral defects in medial femoral condyles of rabbits were created and randomly allocated in one of the following groups: plain scaffold (PU/VAC), scaffold with hAMSCs injected in the implant site (PU/VAC/hAMSC), scaffold with hAMSCs loaded in pectin (PU/VAC/PECT/hAMSC), and no treated defects (untreated). The therapeutic efficacy was assessed by macroscopic, histological, histomorphometric, microtomographic, and ultrastructural analyses at 3, 6, 12, and 24 weeks. Histological results showed that the scaffold was permissive to tissue growth and penetration, an immature osteocartilaginous tissue was observed at early experimental times, with a more accentuated bone regeneration in comparison with the cartilage layer in the absence of any inflammatory reaction.

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

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.

False-Positive Automated Synovial Fluid White Blood Cell Counting Is a Concern for Both Hip and Knee Arthroplasty Aspirates

BACKGROUND

Although false elevation of automated leukocyte (white blood cell [WBC]) counts has been described in the setting of hip corrosion, the more general correlation between manual and automated cell counts among synovial fluid aspirates from hip and knee arthroplasties has not been studied.

METHODS

This retrospective review at one laboratory identified 8607 consecutive synovial fluid samples from arthroplasties and 812 from native knees, each with an automated WBC count > 3000 cells/μL and a corresponding paired reflex manual count. The correlation between automated and manual counts was evaluated, as was the rate of false-positive automated WBC counts.

RESULTS

The correlation between automated WBC counts for native knees, total knee arthroplasties, and total hip arthroplasties was near-perfect, strong, and moderate, respectively. The false-positive rates for automated counts were 4.4%, 10.1%, and 34.3%, respectively (P < .0001). International Consensus Meeting scores and culture positivity demonstrated that manual counts, not automated counts, were correct.

CONCLUSION

The presence of a hip or knee arthroplasty appears to substantially increase the risk of a false-positive automated synovial fluid WBC count. Clinicians evaluating an arthroplasty should exercise caution when interpreting positive automated WBC counts, and consider requesting a reflex manual count, to verify the accuracy of automated cell counting.

How well does synovial fluid gram staining correlate with cultures in native joint infections?

To evaluate the sensitivity and specificity of Gram staining of synovial fluid aspirated from native joints suspected to be infected, we reviewed results of synovial fluid Gram stain and cultures. The sensitivity and specificity of the synovial Gram stain were then calculated. From the 1067 consecutive synovial fluid samples evaluated, 830 samples fulfilled the set criteria. From these 830 synovial fluid samples, organisms were detected by culture technique in only 100 samples; most of which were Gram-positive bacteria (78%). The other 22% comprised Gram-negative bacteria, Fungi and a mixture of growth. Of these, concomitant Gram stain test revealed sensitivity and specificity of 17.0% and 99.7% respectively. Our study demonstrates that the Gram stain technique has low sensitivity in detecting organisms in presumed native joint infections. Our findings demonstrate that the Gram stain test is an unreliable investigation in diagnosing native joint infections.

Factors to Consider When Assessing the Diagnostic Accuracy of Synovial Leukocyte Count in Periprosthetic Joint Infection

Synovial white blood cell (WBC) count and the percentage of polymorphonuclear leucocytes (PMN%) is one of the diagnostic criteria to diagnose a periprosthetic joint infection (PJI). Although the test is widely available, the diagnostic accuracy of proposed cut-off levels are influenced by several factors, such as: the affected joint, co-morbid conditions, the causative microorganism and the gathering and processing of samples in the laboratory. In this narrative review we provide an overview on how and to what extent these factors can affect the synovial WBC count and PMN% in synovial fluid.

Brief Report: Synovial Fluid White Blood Cell Count in Knee Osteoarthritis: Association With Structural Findings and Treatment Response

OBJECTIVE

Osteoarthritis (OA) is a disease with a significant inflammatory component. The aim of this analysis was to determine the relationship between synovial fluid (SF) white blood cell (WBC) count and 2 parameters: disease severity and the reduction in knee pain after intraarticular (IA) steroid injection.

METHODS

Subjects with painful knee OA were recruited for participation in an open-label study of IA steroid therapy. Information was obtained about knee pain using the Knee Injury and Osteoarthritis Outcome Score (KOOS) questionnaire, and a proportion of subjects underwent magnetic resonance imaging (MRI). Prior to injection with 80 mg methylprednisolone acetate, the index knee joint was aspirated and the fluid obtained was forwarded for assessment of SF WBC count.

RESULTS

Information on SF WBC count was available for 55 subjects. An increase in WBC count category (≤100, 101-250, and 251-1,000 cells/mm3 ) was associated with an increase in synovial tissue volume (P = 0.028) and with other MRI-based measures of disease severity. Also, with each increase in SF WBC count category, there was a greater reduction in KOOS score after steroid injection (for WBC count of ≤100 cells/mm3 [referent], mean ± SD 12.5 ± 15.2; for WBC count of 101-250 cells/mm3 , mean ± SD 21.3 ± 20.6 [β coefficient 0.279, P = 0.049]; for WBC count of 251-1,000 cells/mm3 , mean ± SD 29.3 ± 15.2 [β coefficient 0.320, P = 0.024]).

CONCLUSION

Although all participants in the analysis had SF WBC counts within the "normal" range, total SF WBC count appears to be a biomarker for synovitis on MRI and may also predict response to antiinflammatory treatment.

Optimization of Cellular analysis of Synovial Fluids by optical microscopy and automated count using the Sysmex XN Body Fluid Mode

BACKGROUND

This study was planned to assess the impact of pre-treating synovial fluid (SF) samples with hyaluronidase (HY), defining the best procedure for optical microscopy (OM) analysis and evaluating the performance of Sysmex XN-9000 Body Fluid module (XN-BF).

METHODS

The cell count by OM was carried out both with and without HY pre-treatment, and using 3 different types of staining reagents. The evaluation of XN-BF included data comparison with OM (100 SFs), carryover, Limit of Blank (LoB), Limit of Detection (LoD), Limit of Quantitation (LoQ) and linearity.

RESULTS

Unlike cell count in Burker's chamber and staining with Stromatol, pre-treatment with HY and staining with Methylene Blue and Turk's promoted cell clustering. The SF samples pre-treated with HY displayed excellent morphological quality, contrary to samples without HY pre-treatment. Excellent correlation was found between total cells counting with both OM and XN-BF. Satisfactory agreement was also observed between polymorphonuclear neutrophils compared to XN-BF parameter, whereas mononuclear cell count on XN-BF had suboptimal agreement with OM. The carryover was negligible. The LoB, LoD, LoQ and linearity were excellent.

CONCLUSION

XN-BF displays excellent performance, which makes it a reliable and practical alternative to OM for SF samples analysis in clinical laboratories.

Predictors of Septic Arthritis in the Adult Population

Septic arthritis is a devastating condition; well-established criteria for diagnosis exist in the pediatric population, but not for adults. This study evaluated patient factors and laboratory parameters that may be associated with the diagnosis of septic arthritis in adults. A total of 458 knee aspirates for suspected septic arthritis were evaluated with serum and synovial leukocyte counts and differentials as well as Kocher criteria for pediatric septic arthritis. Twenty-two patients (4.8%) had septic arthritis confirmed by a positive synovial fluid culture. Erythrocyte sedimentation rate (ESR) and serum white blood cell (WBC) counts were not statistically different between the 2 groups, with 64% of septic arthritis patients having a normal serum WBC count and 77% being afebrile. Mean synovial fluid WBC count was 26,758 cells/µL and 70,581 cells/µL in the nonseptic and septic groups, respectively. The likelihood ratio for a synovial fluid WBC count greater than 65,000 cells/µL was 2.8 (95% confidence interval, 1.2-6.7). Evaluation receiver operating characteristic curves using synovial WBC counts resulted in a significant area under the curve of 0.66 (P=.02). To achieve 90% specificity, a WBC cutoff of 64,000 cells/µL was required with a corresponding sensitivity of 40%. There was no significant difference in the synovial cell differential of 80% vs 90% in diagnosing infection. Synovial fluid WBC count greater than 64,000 cells/µL yielded the optimal combination of sensitivity and specificity. Polymorphonuclear leukocytes, ESR, serum WBC count, fever, and weight-bearing status were not significant predictors of septic arthritis. This study demonstrates the limited utility of Kocher criteria in the adult population and the importance of synovial leukocyte counts. [Orthopedics. 2016; 39(4):e657-e663.].

Flow cytometry for the microscopy of body fluids in patients with suspected infection

Automating the microscopy of body fluids is challenging, due to the wider range and lower concentrations of cells in these fluids, as opposed to blood, while the viscous nature of some of these fluids can also be problematic. This review shows that there have been major improvements and that newer flow cytometers can have remarkably low limits of quantitation for WBCs. Accurate counting of RBCs is still problematic with many flow cytometers, but this is of no clinical significance. Many flow cytometers can give reasonably accurate WBC differential counts, but detection of eosinophils and neoplastic or other nucleated cells which are not blood cells can still be problematic, hence fail-safe measures are recommended. Cerebrospinal fluid is the most challenging body fluid as it requires the ability to count and differentiate WBCs down to a 'normal range', which is much lower than the diagnostic cut-off values used for serous fluids; precision at or around the cerebrospinal fluid WBC normal range is reduced even with the best flow cytometers, but manual microscopy is even less precise.

Usefulness and limitations of rapid urine dipstick testing for joint-fluid analysis. Prospective single-center study of 98 specimens

OBJECTIVE

To evaluate the diagnostic performance of rapid urine reagent strip testing of joint fluid in separating mechanical from inflammatory disease.

METHODS

In a prospective single-center 12-month study of joint fluid specimens, leukocyte esterase reagent strip testing (LERST) was compared to leukocyte counts used as the reference standard. Leukocyte counts greater than 2000/mm(3) were taken to indicate inflammation. Reproducibility of LERST was evaluated by testing 73 specimens twice and computing Cohen's kappa coefficient.

RESULTS

Ninety-eight joint fluid specimens (26 with mechanical and 72 with inflammatory characteristics) were evaluated. LERST had 79.2% sensitivity, 92.3% specificity, 96.6% positive predictive value, 61.5% negative predictive value, a positive likelihood ratio of 10.3, and a negative likelihood ratio of 0.23. The kappa coefficient was 0.70 (0.53-0.87). Two negative LERSTs a few minutes apart had 80% negative predictive value and a negative likelihood ratio of 0.08.

CONCLUSION

LERST of joint fluid is a rapid means of satisfactorily separating mechanical from inflammatory joint fluids.

Pseudoeosinophilia of synovial fluid is caused by crystals mimicking the distinct light scattering fractions of eosinophilic granules

Automated leukocyte differential counts of synovial fluid (SF) can be influenced by laboratory artefacts. Pseudoeosinophilia of SF has recently been first described in association with monosodium urate and calcium pyrophosphate crystals. This study compared automated measurements of the percentages of SF leukocyte fractions by two haematology analysers in order to elucidate the underlying mechanism of pseudoeosinophilia.

The percentages of the leukocyte fractions of 17 crystal-containing and 28 crystal-free specimens were compared using the Wilcoxon test. Measurements were performed using the Cell-Dyn 3200 and the ADVIA 2120i, which are based on different techniques.

The percentages of eosinophils of the crystal-positive samples determined by the Cell-Dyn 3200 were significantly higher than those assessed by the ADVIA (p<0.0001), whereas the percentages of eosinophils of the controls did not differ significantly between the two devices (p=0.95). The Cell-Dyn 3200 clearly showed the phenomenon of crystal-associated pseudoeosinophilia (p<0.0001), which did not occur in the ADVIA measurements (p=0.28). The percentage of neutrophils was to a lower degree elevated in the crystal group (p=0.015).

It was confirmed that SF crystals interfere with the typical light scattering fractions of leukocyte granules and may thus lead to spuriously elevated percentages of eosinophils and neutrophils in SF specimens.

Evidence-based diagnostics: adult septic arthritis

BACKGROUND

Acutely swollen or painful joints are common complaints in the emergency department (ED). Septic arthritis in adults is a challenging diagnosis, but prompt differentiation of a bacterial etiology is crucial to minimize morbidity and mortality.

OBJECTIVES

The objective was to perform a systematic review describing the diagnostic characteristics of history, physical examination, and bedside laboratory tests for nongonococcal septic arthritis. A secondary objective was to quantify test and treatment thresholds using derived estimates of sensitivity and specificity, as well as best-evidence diagnostic and treatment risks and anticipated benefits from appropriate therapy.

METHODS

Two electronic search engines (PUBMED and EMBASE) were used in conjunction with a selected bibliography and scientific abstract hand search. Inclusion criteria included adult trials of patients presenting with monoarticular complaints if they reported sufficient detail to reconstruct partial or complete 2 × 2 contingency tables for experimental diagnostic test characteristics using an acceptable criterion standard. Evidence was rated by two investigators using the Quality Assessment Tool for Diagnostic Accuracy Studies (QUADAS). When more than one similarly designed trial existed for a diagnostic test, meta-analysis was conducted using a random effects model. Interval likelihood ratios (LRs) were computed when possible. To illustrate one method to quantify theoretical points in the probability of disease whereby clinicians might cease testing altogether and either withhold treatment (test threshold) or initiate definitive therapy in lieu of further diagnostics (treatment threshold), an interactive spreadsheet was designed and sample calculations were provided based on research estimates of diagnostic accuracy, diagnostic risk, and therapeutic risk/benefits.

RESULTS

The prevalence of nongonococcal septic arthritis in ED patients with a single acutely painful joint is approximately 27% (95% confidence interval [CI] = 17% to 38%). With the exception of joint surgery (positive likelihood ratio [+LR] = 6.9) or skin infection overlying a prosthetic joint (+LR = 15.0), history, physical examination, and serum tests do not significantly alter posttest probability. Serum inflammatory markers such as white blood cell (WBC) counts, erythrocyte sedimentation rate (ESR), and C-reactive protein (CRP) are not useful acutely. The interval LR for synovial white blood cell (sWBC) counts of 0 × 10(9)-25 × 10(9)/L was 0.33; for 25 × 10(9)-50 × 10(9)/L, 1.06; for 50 × 10(9)-100 × 10(9)/L, 3.59; and exceeding 100 × 10(9)/L, infinity. Synovial lactate may be useful to rule in or rule out the diagnosis of septic arthritis with a +LR ranging from 2.4 to infinity, and negative likelihood ratio (-LR) ranging from 0 to 0.46. Rapid polymerase chain reaction (PCR) of synovial fluid may identify the causative organism within 3 hours. Based on 56% sensitivity and 90% specificity for sWBC counts of >50 × 10(9)/L in conjunction with best-evidence estimates for diagnosis-related risk and treatment-related risk/benefit, the arthrocentesis test threshold is 5%, with a treatment threshold of 39%.

CONCLUSIONS

Recent joint surgery or cellulitis overlying a prosthetic hip or knee were the only findings on history or physical examination that significantly alter the probability of nongonococcal septic arthritis. Extreme values of sWBC (>50 × 10(9)/L) can increase, but not decrease, the probability of septic arthritis. Future ED-based diagnostic trials are needed to evaluate the role of clinical gestalt and the efficacy of nontraditional synovial markers such as lactate.

Calcium pyrophosphate and monosodium urate crystals in synovial fluid as a cause of pseudoeosinophilia

BACKGROUND

Synovial fluid (SF) leukocytes can be counted microscopically in a Neubauer chamber or by automated procedures using haematology analysers. Knowledge of laboratory artefacts is crucial for the correct interpretation of results obtained using automated methods. SF pseudoeosinophilia has recently been described as a new artefact in patients with crystal-related arthropathies. We investigated whether pseudoeosinophilia of SF is restricted to crystal-related disorders, or if it may also occur in other arthropathies.

METHODS

We compared the percentages of eosinophils in 120 crystal containing SF samples with 185 crystal-free specimens using the Wilcoxon test. Crystal positive samples, determined by polarised microscopy, contained at least two monosodium urate or calcium pyrophosphate crystals per 10 high power fields (630× magnification). True SF eosinophilia was ruled out by microscopic examination of stained slides.

RESULTS

Crystal positive samples had significantly higher percentages of eosinophils than the controls (p<0.0001). No significant differences between the two crystal types were found (p=0.693). Thus, pseudoeosinophilia was significantly correlated with the presence of crystals, and none of the distinct crystal types was more likely to be associated with pseudoeosinophilia.

CONCLUSIONS

In this study, SF pseudoeosinophilia was confirmed as a crystal-related laboratory artefact which has to be considered in the interpretation of automated SF leukocyte differential counts.

Use of the Cell-Dyn Sapphire hematology analyzer for automated counting of blood cells in body fluids

The enumeration and identification of blood cells in body fluids offers important information for the diagnosis and treatment of various medical conditions. Manual microscopic methods (hemacytometer total cell count and cytocentrifuged differential count) have inherent analytic and economic disadvantages but are still considered the "gold standard" methods. We evaluated the analytic and clinical performance of the Cell-Dyn Sapphire hematology analyzer (Abbott Diagnostics Division, Santa Clara, CA) for automated blood cell counting and leukocyte differential counting in cerebrospinal fluid, serous fluid (peritoneal and pleural fluid), and continuous ambulatory peritoneal dialysis fluid, and we compared the performance with the respective manual methods. In the present article, we describe its applicability for the distinct body fluids, and we highlight limitations and caveats.

Gross synovial fluid analysis in the differential diagnosis of joint effusion

AIMS

To develop an objective and easy to complete standardised questionnaire for documentation of synovial fluid (SF) gross appearance and use it in the assessment of patients presenting to the rheumatology service with a joint effusion.

METHODS

A standardised questionnaire to record the gross appearance of SF was developed. Interobserver error in recorded observations and direct gross analysis of synovial fluid between four observers was calculated in a pilot study. In a prospective study over 8 months, SF gross analysis and cell count were documented in all patients presenting with a joint effusion. Fusch Rosenthal manual counting chamber was used for calculating SF cell counts.

RESULTS

There was good interobserver agreement on direct gross analysis and between questionnaire assessors (mean kappa 0.889). 80 SF samples were collected. Gross analysis was performed in all samples and cell count in 72. Of the specimens thought to be inflammatory on gross analysis, 31% were found to be non-inflammatory based on cell count; however, 12 of these patients had an established inflammatory arthritis. Gross analysis had a sensitivity of 94% and specificity of 58% when used to determine whether SF is inflammatory or non-inflammatory. The positive and negative predictive values were 0.69 and 0.91 respectively.

CONCLUSIONS

SF cell count did not add any information when SF gross analysis suggested a non-inflammatory process. Gross analysis was better than cell count to determine a potentially septic joint fluid. Further work needs to be done on the value of SF cell counts if gross analysis suggests the fluid to be inflammatory.

Evaluation of a standardized procedure for [corrected] microscopic cell counts [corrected] in body fluids

A standardized urinalysis and manual microscopic cell counting system was evaluated for its potential to reduce intra- and interoperator variability in urine and cerebrospinal fluid (CSF) cell counts. Replicate aliquots of pooled specimens were submitted blindly to technologists who were instructed to use either the Kova system with the disposable Glasstic slide (Hycor Biomedical, Inc., Garden Grove, CA) or the standard operating procedure of the University of California-Irvine (UCI), which uses plain glass slides for urine sediments and hemacytometers for CSF. The Hycor system provides a mechanical means of obtaining a fixed volume of fluid in which to resuspend the sediment, and fixes the volume of specimen to be microscopically examined by using capillary filling of a chamber containing in-plane counting grids. Ninety aliquots of pooled specimens of each type of body fluid were used to assess the inter- and intraoperator reproducibility of the measurements. The variability of replicate Hycor measurements made on a single specimen by the same or different observers was compared with that predicted by a Poisson distribution. The Hycor methods generally resulted in test statistics that were slightly lower than those obtained with the laboratory standard methods, indicating a trend toward decreasing the effects of various sources of variability. For 15 paired aliquots of each body fluid, tests for systematically higher or lower measurements with the Hycor methods were performed using the Wilcoxon signed-rank test. Also examined was the average difference between the Hycor and current laboratory standard measurements, along with a 95% confidence interval (CI) for the true average difference. Without increasing labor or the requirement for attention to detail, the Hycor method provides slightly better interrater comparisons than the current method used at UCI.

Measurement of total and differential white blood cell counts in synovial fluid by means of an automated hematology analyzer

We developed a rapid and accurate method for quantifying total and differential white blood cell (WBC) counts by pretreating synovial fluid with hyaluronidase and using an automated hematology analyzer. Forty-seven samples of synovial fluid that had been placed in blood-collection tubes containing ethylenediamine- N,N,N',N' -tetraacetic acid as an anticoagulant were treated with hyaluronidase at 37 degrees C for 10 minutes, and then the total and differential WBC counts were determined by means of the automated hematology analyzer. Results were compared with those achieved by traditional manual counting methods. For the automated method, the coefficient of variation values for within-run precision of the WBC count were 5.27%, 3.56%, and 3.01% at 0.54, 1.12, and 2.05 x 10(9) /L, respectively; the run-to-run coefficient of variation values was less than 10.0%. The total and differential WBC counts obtained by this automated method showed good correlation with those obtained by the hemocytometer method ( r = .998; P < .0001; regression formula, y = 0.986 x - 0.072). Bland-Altman plots indicated no significant discrepancy between the methods. Our evaluation supports the use of this automated hematology analyzer method to measure total and differential WBC counts, which should aid clinical diagnosis.

Synovial fluid analysis

Synovial fluid (SF) accumulates in the joint cavity in different conditions; this review outlines the data from those analyses that help in their differential and definitive diagnosis. The gross appearance of the fluid can provide a quick bedside orientation with regard to the amount of inflammation present in the joint: totally transparent SF originates in non-inflammatory conditions--of which osteoarthritis is the most common--and the amount of turbidity grossly relates to the amount of inflammation. Most turbid to purulent fluids usually come from infected joints, but exceptions are not uncommon. The white cell count offers quantitative information, but the boundaries between non-inflammatory and inflammatory SF and between this and septic fluid are very hazy and figures have to be interpreted in the clinical setting. Detection and identification of monosodium urate (MSU) and calcium pyrophosphate dihydrate (CPPD) crystals allow a precise diagnosis of gout and CPPD crystal-related arthropathy. Only one in five CPPD crystals have sufficient birefringence for easy detection and they are easily missed if searched for only using a polarised microscope. Instructions for beginners are given. Proper microbiological studies of the SF is the key to the diagnosis of infectious conditions.