In hemorrhage involving the subarachnoid space, the findings depend on the time interval following hemorrhage when the patient is examined. It takes about 4 hours (literature range, 2-48 hours) to develop xanthochromia. Therefore, CSF obtained very early may have a colorless supernatant. Initially, the WBC count and protein level are proportional to the amount of CSF blood (about 1 WBC/700 RBCs and 1 mg protein/1,000 RBCs). Later, the WBC count may rise, sometimes to levels greater than 1,000/cu mm, with predominance of segmented neutrophils. This may raise the question of intracranial infection. This rise is usually attributed to meningeal irritation by the blood. Protein also is initially correlated to RBC count but later may rise out of proportion to the number of RBCs as the WBCs increase and the RBCs lyse and disappear. Usually by 3 weeks after onset, xanthochromia has disappeared and both protein and cell count have returned to normal.