Is procalcitonin (PCT) a helpful test to support or rule out bacterial meningitis?

Procalcitonin in Diagnosing Bacterial Meningitis

Procalcitonin is a valuable biomarker for differentiating bacterial from viral meningitis, with high sensitivity and specificity when using appropriate cutoff values. 1

Diagnostic Value of Procalcitonin

• Serum procalcitonin levels are significantly elevated in bacterial meningitis compared to viral meningitis, making it a useful diagnostic marker 1
• In children with meningitis, using a cutoff of 15.0 mg/L, procalcitonin has shown 94% sensitivity and 100% specificity for diagnosing bacterial meningitis 1
• In adults, serum procalcitonin concentrations >10.2 ng/mL have demonstrated sensitivity and specificity of up to 100% for the diagnosis of bacterial meningitis 1
• More recent studies suggest lower cutoff values may be appropriate - a threshold of 0.5 ng/mL showed 95.45% sensitivity and 84.61% specificity in children 2
• A threshold of 0.93 ng/mL was found to distinguish between bacterial and viral meningitis with 100% accuracy in adult patients 3

Prognostic Value

• Beyond diagnosis, procalcitonin levels can predict outcomes in bacterial meningitis 4
• High serum procalcitonin levels (>7.26 ng/mL) independently predict mortality in patients with bacterial meningitis, with a 9-fold higher risk of death (OR=9.09,95% CI: 1.74-47.12) 4

Comparison with Other Biomarkers

• Procalcitonin outperforms other traditional markers like C-reactive protein (CRP) and leukocyte count in differentiating bacterial from viral meningitis 5, 2
• In ROC curve analysis, procalcitonin showed maximum area under curve (0.991) compared to total leukocyte count and CSF cytochemistry parameters 2
• While CSF lactate has good sensitivity and specificity for differentiating bacterial from aseptic meningitis, its value is limited in patients who received antibiotic pretreatment 1

Special Considerations in Post-Neurosurgical Patients

• Procalcitonin in CSF may be particularly valuable in diagnosing bacterial meningitis in post-neurosurgical patients 6
• The median PCT CSF:plasma ratio was found to be 5.18 in post-neurosurgical meningitis compared to 0.18 in community-acquired meningitis 6

Limitations and Caveats

• Despite its high diagnostic value, procalcitonin should not be used in isolation to determine whether an individual patient should receive antimicrobial therapy 1
• False-negative results have been reported (sensitivity as low as 69% in some studies) 1
• Other conditions can cause elevated procalcitonin levels, including severe inflammatory states of non-infectious origin, cerebral hypoxia/ischemia, and trauma 7
• Current guidelines note that because measurement of serum procalcitonin concentrations is not readily available in all clinical laboratories, definitive recommendations on its routine use cannot be made at this time (C-II) 1
• In clinical practice, other bacterial infections such as sepsis and pneumonia may be included in the differential diagnosis of bacterial meningitis, and in these situations procalcitonin may be less specific for the diagnosis of bacterial meningitis 1

Practical Approach

• Obtain blood cultures before starting antibiotics, as they may be positive in 40-90% of bacterial meningitis cases depending on the pathogen 1
• Do not delay antibiotic treatment while waiting for procalcitonin results; treatment should be initiated within one hour of presentation in suspected bacterial meningitis 1, 8
• Consider procalcitonin testing as an adjunct to standard CSF analysis (cell count, protein, glucose) and microbiological tests (Gram stain, culture) 1
• Use procalcitonin results to help guide decisions about continuing or discontinuing antibiotics, particularly in cases with equivocal CSF findings 5, 2