Combining cytology and microcrystal detection in nonpurulent joint fluid benefits the diagnosis of septic arthritis.
OBJECTIVE
To evaluate the performance of combined cytology and microcrystal detection in joint fluid for diagnosing septic arthritis.


METHODS
Retrospective single-center study of joint fluid samples from patients with manifestations suggesting acute or chronic arthritis. The absolute leukocyte count (/mm3) was recorded; as well as the differential counts, particularly of neutrophils (%). Microcrystals were sought and bacteriological cultures performed. Septic arthritis was defined as positive cultures of joint fluid or blood samples. Diagnostic performance was assessed based on sensitivity, specificity, the receiver-operating characteristics (ROC) curve with the area under the curve (AUC), and the positive and negative likelihood ratios (LR+ and LR-).


RESULTS
Two hundred and eight joint fluid samples were included. The diagnoses were septic arthritis (n=28), chondrocalcinosis (n=41), gout (n=28), rheumatoid arthritis (n=33), spondyloarthritis (n=31), osteoarthritis (n=18), and undifferentiated arthritis (n=29). Among cytological parameters, those having the best diagnostic performance were the neutrophil count (cutoff, >50,000/mm3), the leukocyte count (cutoff, >50,000/mm3), and the percentage of neutrophils (cutoff, >95%); corresponding LR+ values were 8.93, 5.76, and 4.55, respectively. Neutrophil percentages lower than 80% had an LR- value of 0.07. Combining these cytological variables with the absence of crystals improved the diagnostic performance, yielding LR+ values of 11.36, 10.94, and 10.82 for neutrophils >95%, neutrophils >50,000/mm3, and leukocytes >50,000/mm3, respectively.


CONCLUSIONS
Combining cytological characteristics of joint fluid with the absence of crystals benefits the diagnosis of septic arthritis.
Service de Rhumatologie, CHU de Rennes Hôpital Sud, 16, boulevard de Bulgarie, BP 90347, 35203 Rennes Cedex 2, France.
Marine
M
Ferreyra
Service de Rhumatologie, CHU de Rennes Hôpital Sud, 16, boulevard de Bulgarie, BP 90347, 35203 Rennes Cedex 2, France; INSERM UMR 991, 35203 Rennes, France. Electronic address: guillaume.coiffier@chu-rennes.fr.
Guillaume
G
Coiffier
Service de Rhumatologie, CHU de Rennes Hôpital Sud, 16, boulevard de Bulgarie, BP 90347, 35203 Rennes Cedex 2, France; INSERM UMR 991, 35203 Rennes, France.
Jean-David
JD
Albert
Service de Rhumatologie, CH de Vannes, 20, boulevard Général-Maurice-Guillaudot, 56000 Vannes, France.
Claire
C
David
Service de Rhumatologie, CHU de Rennes Hôpital Sud, 16, boulevard de Bulgarie, BP 90347, 35203 Rennes Cedex 2, France.
Aleth
A
Perdriger
Service de Rhumatologie, CHU de Rennes Hôpital Sud, 16, boulevard de Bulgarie, BP 90347, 35203 Rennes Cedex 2, France; INSERM UMR 991, 35203 Rennes, France.
Pascal
P
Guggenbuhl
D000208:Acute Disease; D000328:Adult; D000367:Age Factors; D000368:Aged; D000704:Analysis of Variance; D001170:Arthritis, Infectious / Q000175:diagnosis* / Q000453:epidemiology* / Q000473:pathology; D002097:C-Reactive Protein / Q000032:analysis*; D002908:Chronic Disease; D015331:Cohort Studies; D003460:Crystallization; D003581:Cytodiagnosis; D005260:Female; D006801:Humans; D015994:Incidence; D007958:Leukocyte Count; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D011379:Prognosis; D012372:ROC Curve; D012189:Retrospective Studies; D018570:Risk Assessment; D012720:Severity of Illness Index; D012737:Sex Factors; D013582:Synovial Fluid / Q000737:chemistry* / Q000166:cytology*
D002097:C-Reactive Protein
Cytology; Diagnosis; Joint fluid; Microcrystals; Septic arthritis