Bloody tap? Postoperative shunt infection? How to do a CSF erythrocyte correction…

So it must have been a bloody tap the last time when we got an inflammatory CSF with 375 WBC/µl out of this guy on our ICU. A week later we come back to check on the cell count and it comes red. Not just one glass but all of them. Is the infection gone then?

We run through the arithmetic, using the standard formula for the cell index

WBC [CSF] / WBC [blood]
RBC [CSF] / RBC [blood]

Obviously the ratio of cells in the CSF and blood should be the same unless there is some autochthonic cell “production” – this is quite similar to Reiber’s ratios for quantitative immunoglobulin production.

A value of the index of > 5,2 or a rise by more than 4 is purported to be specific for local infection.

Sources? Hard to say. This is probably neurosurgical folklore. I did not find a proper reference for it, but there is some data by  Schmutzhard of eVD patients to support it.