Bedside Test Can Help Rule Out Septic Arthritis in Native Joints

NEW YORK (Reuters Health) – Leucocyte esterase (LE) dipstick testing of synovial fluid aspirate can help rule out septic arthritis in adults presenting to the emergency department with a hot, inflamed native joint, report researchers in the U.K.

LE testing has high negative predictive value (NPV) when evaluating joint fluid for suspected infection, Dr. Thomas Knapper of North Bristol NHS, Westbury on Trym, and colleagues report in Emergency Medicine.

“While it cannot distinguish crystal arthropathy from septic joints, this test may help to decrease diagnostic uncertainty and improve adult patient management, safe discharge and flow in the emergency setting,” they say.

Suspected septic arthritis is common in adults visiting the ED and the underlying cause is often not due to infection. Currently there is no widely accepted bedside test or marker to differentiate infectious from non-infectious joint swellings, they explain in their paper.

LE testing is sensitive and specific when evaluating suspected prosthetic-joint infections. But less is known about the value of LE testing for native-joint infection in adults, they note.

To investigate, Dr. Knapper and colleagues studied 80 adults (mean age, 71; 74% men) from three emergency departments in England with suspected native-joint septic arthritis.

Five patients had a positive 48-hour culture (the gold standard), with one case each of Staphylococcus aureus, Pseudomonas aeruginosa, and beta hemolytic Streptococcus group C, G and B.

All five of these patients had a positive LE test (>=2+ leucocytes based on the test strip color; sensitivity, 100%; 95% confidence interval, 47.8% to 100%), while the Gram stain was positive in only one case (sensitivity, 20%; 95% CI, 0.51% to 71.6%).

Twenty-three LE tests were read negative or 1+, all with negative 48-hour culture results, yielding a NPV of 100% (95% CI, 82.1% to 1.00%) for a negative LE test.

However, specificity of a positive LE test was poor at 30.7% (95% CI, 20.5% to 42.4%) and a positive predictive value (PPV) of only 8.8% (95% CI, 7.64% to 10.1%).

The researchers determined that 57 orthopedic bed-days could have potentially been saved by immediately discharging those with a negative LE test. “Discharging these patients could have achieved potential savings of £17271 ($23,962) across two of the trusts in this cohort,” they calculate.

They recommend further multicenter studies with larger sample sizes to corroborate these results.

The study had no specific funding and the authors have no relevant disclosures.

SOURCE: Emergency Medicine, online March 10, 2021.

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