When blood is present in a CSF specimen, it is necessary to determine whether the blood is due to a traumatic puncture or a pathologic condition. Table 4 describes several clues to help make this distinction.
Table 4. Differentiating Traumatic Taps and Subarachnoid Hemorrhages.| Conditions | Traumatic Tap | Subarachnoid Hemorrhage |
| Blood Content | Blood in Tube 1 is greater than in tubes 2, 3, 4 | Blood is evenly distributed in all tubes |
| Supernatant Color after Centrifugation | Clear | Pink or yellow |
| Clotting | Blood clots on standing | Blood does not clot on standing |
