CSF Glucose Ratio in Bacterial Meningitis Diagnosis

Diagnostic Thresholds

A CSF-to-blood glucose ratio <0.4 is highly specific for bacterial meningitis, and a ratio <0.23 predicts bacterial etiology with 99% certainty when combined with other CSF parameters 1
The American Academy of Pediatrics recommends a CSF/blood glucose ratio <0.4 as 80% sensitive and 98% specific for bacterial meningitis in children ≥2 months of age 2
A CSF/blood glucose ratio <0.23 is an individual predictor of bacterial meningitis with 99% certainty 1
Absolute CSF glucose <34 mg/dL predicts bacterial meningitis with 99% certainty 1

In bacterial meningitis, CSF glucose is typically <40 mg/dL in 50-60% of cases 2
A CSF glucose <35 mg/dL with CSF/blood ratio <0.23 indicates bacterial etiology 3
In viral meningitis, CSF/blood glucose ratio is typically >0.36 and often normal 4, 5
In tuberculous meningitis, CSF/blood glucose ratio is typically <0.5 (very low) 6
Absolute CSF glucose <2.2 mmol/L has 68% sensitivity and 96% specificity for TB meningitis 6

A ratio <0.23 indicates bacterial meningitis is highly likely (99% certainty when combined with other parameters) 1
The combination of CSF glucose <34 mg/dL, CSF/blood ratio <0.23, protein >120 mg/dL, WBC >12,000/mm³, or neutrophils >11,000/mm³ predicts bacterial meningitis with 99% certainty 1

Term neonates have higher normal CSF/blood glucose ratios 2
A ratio of 0.6 is considered abnormal in neonates (not 0.4 as in older children) 2
The Infectious Diseases Society of America recommends that CSF lactate measurements should not be relied upon after antibiotics are given 4
The CSF/blood glucose ratio remains accurate even after pre-hospital antibiotic administration, but CSF lactate measurements lose diagnostic value after antibiotics are given 4

The American Academy of Pediatrics and the Infectious Diseases Society of America recommend considering serum inflammatory markers, such as CRP and procalcitonin, when the CSF/serum glucose ratio is 0.23-0.36, especially if the Gram stain is negative 7, 8

In postoperative neurosurgical patients, a CSF lactate level greater than 4.0 mmol/L was found to be superior to the glucose ratio for diagnosing bacterial meningitis, but this does not apply to community-acquired meningitis 7, 8