Acid phosphatase activity of cerebrospinal fluid cells in leptomeningeal haemorrhage

One hundred and twenty samples of haemorrhagic spinal fluid were examined by acid phosphatase staining. This enzyme activity starts to appear in mono-histiocytic cells 2 days after bleeding and increases up to the 5th day. After 1 week the activity decreases rapidly. Similar results are found in mixtures of incubated clear spinal fluid, to which blood is added. Acid phosphatase staining is a useful additional method for determination of the age of a leptomeningeal bleed.