CSF White Cell Correction
Neurology
How many of those white cells came from a traumatic tap rather than from the CSF.
How it is calculated
- Blood introduced by a traumatic tap brings white cells with it, in the same ratio they occur in the patient's own blood.
- Predicted CSF white cells = CSF red cells × (blood white cells ÷ blood red cells).
- Adjusted CSF white cells = the observed count minus that prediction.
- All four counts must be in the same units. A blood count reported as 7.2 × 10⁹/L is 7,200 per microlitre, and 4.5 × 10¹²/L is 4,500,000 per microlitre — the unit mismatch is the commonest source of a wrong answer, and the tool checks for it.
- The rules of thumb, one white cell per 500 or per 1000 red cells, are shown alongside. They are the same calculation with an assumed blood ratio instead of the measured one.
- The correction is an estimate. A genuinely infected CSF can still be misread in either direction, so it should never be the only reason to withhold treatment.
References
- Standard laboratory medicine — the ratio method for correcting CSF cell counts after a traumatic lumbar puncture.
About these tools
OcuLearning Clinical Tools is part of an educational platform. These calculators are provided for learning and reference, and are not medical advice, a diagnosis, or a treatment recommendation.