GS in septic arthritis

 Q: The sensitivity of gram stain in septic arthritis is? (select one)

A) reliable

B) not very reliable

Answer: B

The gram stain in septic arthritis is positive in only some cases and the sensitivity is only 30 to 50 percent. There is a good chance of false-positive gram stain as precipitated crystal violet (gentian violet) and mucin in synovial fluid may mimic gram-positive cocci. 

False-negative results are due to the presence of crystals and/or clotting in the synovial fluid.

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References:

1. Margaretten ME, Kohlwes J, Moore D, Bent S. Does this adult patient have septic arthritis? JAMA 2007; 297:1478.

2. Stirling P, Faroug R, Amanat S, et al. False-negative rate of gram-stain microscopy for diagnosis of septic arthritis: suggestions for improvement. Int J Microbiol 2014; 2014:830857.

3. Stirling P, Tahir M, Atkinson HD. The Limitations of Gram-stain Microscopy of Synovial Fluid in Concomitant Septic and Crystal Arthritis. Curr Rheumatol Rev 2018; 14:255.