Calprotectin levels separate septic arthritis from other inflammatory arthritides
medwireNews: Levels of calprotectin in the synovial fluid can be used to discriminate patients with septic arthritis from those with pseudogout and rheumatoid arthritis (RA), shows a report published in Rheumatology.
Athan Baillet (University Grenoble-Alpes, France) and co-authors say that “[e]arly discrimination of septic arthritis from other acute arthritis is crucial” because “early antibiotic therapy and debridement surgery are associated with better prognosis.”
However, they add that “rapid diagnosis by direct examination of the Gram stain” is not always possible because antibiotic use can lead to a negative result.”
Baillet and team found that patients with septic arthritis (n=26) had a significantly higher level of synovial calprotectin than those with pseudogout (n=28) or RA (n=20), at median values of 190.0 versus 46.2 and 66.8 mg/L, respectively.
And in a multivariable analysis adjusted for age, sex, and synovial fluid neutrophil count, synovial fluid calprotectin level was the only independent biomarker that significantly discriminated between septic arthritis and other inflammatory arthritides).
Indeed, at the optimal cutoff of 150 mg/L, as determined by area under the receiver operating characteristic curve analysis, calprotectin discriminated septic arthritis from non-septic inflammatory arthritis with a sensitivity of 76% and a specificity of 94%. The positive and negative predictive values (PPV and NPV) were 86% and 88%, respectively, while the positive and negative likelihood ratios were 12.2 and 0.26, respectively.
Lowering the cutoff to 52 mg/L increased sensitivity to 96% but decreased specificity to 44%. The PPV, NPV, and positive and negative likelihood ratios at this cutoff were 47%, 95%, 1.71, and 0.09, respectively.
The researchers note that there was no significant difference in synovial calprotectin levels among patients with septic arthritis caused by Staphylococcus spp., Streptococcus spp., or other bacteria. Nor was there a difference between patients with an infected prosthetic joint and those with an infected native joint.
Baillet and colleagues point out that patients with gout were excluded from the study “in order to compare septic arthritis with a homogeneous control group.”
However, they say that this exclusion “may represent a limitation for the external validity of [the] study, as gout and septic arthritis have similar clinical features.”
The study authors conclude that “further studies are required before the implementation of this assay in daily practice,” because “little is known about the stability of calprotectin in synovial fluid.”
They add: “Validation of calprotectin as a clinically relevant biomarker for septic arthritis in an independent cohort is needed to pinpoint its usefulness in daily practice.”
By Laura Cowen
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