Thwaites Index (Tuberculous vs Bacterial Meningitis)
The Thwaites diagnostic index (Thwaites and colleagues 2002) distinguishes tuberculous from bacterial meningitis in adults.
Open the calculator → Runs in your browser. Data leaves only if you deliberately send a problem report from the interactive tool.
Example
- Age 36 years or older?
- Yes
- Blood white cell count 15,000 cells/uL or more?
- No
- Duration of illness 6 days or more?
- Yes
- CSF total white cell count 900 cells/uL or more?
- No
- CSF neutrophils 75 percent or more?
- No
Result: Thwaites -3, favors tuberculous meningitis.
The tool opens with these values already filled in. Replace them with your own.
What the result means
- 4 or less
- Favors tuberculous meningitis. This score runs in the opposite direction to most: low is the tuberculous end.
- Above 4
- Favors bacterial meningitis.
- Failure modes
- Specificity collapses in partially treated bacterial meningitis and in HIV-positive adults. Derived in HIV-negative Vietnamese adults.
- Scope
- Discriminates two diagnoses only. Says nothing about viral, fungal, autoimmune, or malignant causes of a lymphocytic CSF.
What you enter
- Age 36 years or older?
- Blood white cell count 15,000 cells/uL or more?
- Duration of illness 6 days or more?
- CSF total white cell count 900 cells/uL or more?
- CSF neutrophils 75 percent or more?
Full field descriptions
- Age 36 years or older? [yes = +2; no = 0] Older age pulls toward bacterial meningitis.
- Blood white cell count 15,000 cells/uL or more? [yes = +4; no = 0] A high peripheral white count pulls toward bacterial meningitis.
- Duration of illness 6 days or more? [yes = -5; no = 0] The only negative weight, and the largest. A longer history is the strongest single pull toward tuberculous meningitis.
- CSF total white cell count 900 cells/uL or more? [yes = +3; no = 0] A high CSF cell count pulls toward bacterial meningitis.
- CSF neutrophils 75 percent or more? [yes = +4; no = 0] A neutrophil-predominant CSF pulls toward bacterial meningitis.
How this is calculated
- Weights
- Age 36 or older +2, blood WBC 15,000/uL or more +4, illness 6 days or more -5, CSF WBC 900/uL or more +3, CSF neutrophils 75 percent or more +4.
Thwaites GE, Chau TTH, Stepniewska K, et al. Diagnosis of adult tuberculous meningitis by use of clinical and laboratory features. Lancet. 2002;360(9342):1287-1292. Read the source ↗
A reference and educational tool. Not medical, legal, or financial advice, and not a substitute for clinician judgment.