'poor man test' for septic arthritis

Q: What is the 'poor man's test' for septic arthritis?

Answer: Measuring the strength of synovial fluid leukocyte esterase in the urine "dipstick" test

It is an art to practice Medicine in a resource-limited country(RLC)! Septic arthritis is more common in RLCs. 

Exotic tests like polymerase chain reaction (PCR) or matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectometry may not be available at many places. Aspirating synovial fluid and measuring the strength of synovial fluid leukocyte esterase using a simple urine "dipstick" test, usually available in units/wards, can guide a clinician in initiating antibiotics.

Ideally, synovial fluid and blood cultures x2 should be obtained before starting antibiotics, and synovial fluid should be sent for Gram stain, bacterial culture, white blood cell count with differential, and assessment of crystals (monosodium urate and calcium pyrophosphate crystal deposition) with a polarizing microscope.

Another tip is NOT to rely on synovial fluid glucose, lactate, or pH, as they are very unreliable in septic arthritis.

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References: 

1. Aslani H, Pasha Zanoosi MR, Navali AM. Urine Dipstick Leukocyte Esterase in the Rapid Diagnosis of Septic Arthritis. Arch Bone Jt Surg. 2022 Jan;10(1):38-44. doi: 10.22038/ABJS.2021.47573.2334. PMID: 35291247; PMCID: PMC8889425.

2. Mirghaderi P, Pahlevan-Fallahy MT, Mahmoudi J, Mortazavi SMJ. Determining the accuracy of the leukocyte esterase reagent strip test in the rapid diagnosis of adult septic arthritis. Adv Rheumatol. 2024 Aug 30;64(1):65. doi: 10.1186/s42358-024-00409-4. PMID: 39215379.

3. Dey M, Al-Attar M, Peruffo L, et al. Assessment and diagnosis of the acute hot joint: a systematic review and meta-analysis. Rheumatology (Oxford) 2023; 62:1740.