Q; Which test would be better in predicting septic arthritis?

Answer:  CRP

An elevated CRP (C-reactive protein) is helpful in determining the presence of a septic joint. The ESR and CRP are almost always raised on admission, CRP being more specific in diagnostics. Both elevated erythrocyte sedimentation rate (ESR) or C-reactive protein (CRP) is useful in following response to therapy.

 

Reference: Usefulness of CRP and ESR in predicting septic joints South Med J. 2010 Jun;103(6):522-6.