Table 3.

Acute Phase Reactants in Specific Infections

Clinical Infection	Acute-phase reactant (ESR-mm/hour, CRP-mg/L, PCT-ng/mL)
Cellulitis and Erysipelas Necrotizing Skin and Soft Tissue Infections (NSSTIs)	CRP >70 and ESR >50 have a higher predictive value for the duration of hospital stay, which is an indirect index of severity [14, 15]. CRP >150 may suggest a higher likelihood of NSSTI [16]. PCT ratio of more than 1.14 between postoperative day 1 and day 2 after surgical debridement associated with favorable clinical recovery [18].
Osteomyelitis Spondylodiscitis Prosthetic Joint Infection	CRP >32 and ESR >70 helpful in distinguishing osteomyelitis from cellulitis in diabetic foot infections [19, 50]. CRP, PCT decrease rapidly with treatment. Fall in previously elevated ESR is a marker for response to treatment [20, 50]. Both ESR (median value 60) and CRP have high sensitivity for diagnosis of pyogenic spondylodiscitis. Decreasing values (25–50%) in the first 4 weeks of treatment suggest favorable prognosis [22, 23]. CRP may remain elevated for up to 6 weeks and ESR for up to 26 weeks after prosthetic joint surgery. Serum IL-6, CRP, and ESR have the best diagnostic value. Likelihood of infection very low if both ESR and CRP are normal. Procalcitonin has a low sensitivity [26, 27].
Meningitis Neurosurgical infections	Serum and cerebrospinal PCT levels likely have a high diagnostic accuracy in bacterial meningitis [44, 45]. CSF lactate at a cutoff of 35 mg/dL has a high negative likelihood ratio for distinguishing bacterial from viral meningitis [51]. Serum PCT levels of >0.15 have a high diagnostic value for bacterial infections after neurosurgical procedures [46, 47].
Infective Endocarditis	An initial value of PCT > 0.5 is predictor for poor outcome. High levels of CRP (>122) after first week of treatment and slow decline are indicators of poor outcome [48, 49].
Pyelonephritis in children	PCT level >0.5 is associated with high likelihood of pyelonephritis and renal scars in pediatric patients with urinary tract infection [52].

Abbreviations: CRP, C-reactive protein; CSF, cerebrospinal fluid; ESR, erythrocyte sedimentation rate; IL, interleukin; PCT, procalcitonin.