Management of Red Blood Cells on Lumbar Puncture
When red blood cells (RBCs) are found on lumbar puncture, they should be carefully interpreted to distinguish between a traumatic tap and true subarachnoid hemorrhage, with management decisions based on RBC count, distribution pattern, and clinical context.
Differentiating Traumatic Tap from True Subarachnoid Hemorrhage
RBC Count Interpretation
Final tube RBC count is more valuable than differential counts between tubes 1
- RBC < 100/mm³ in final tube: Very low likelihood of subarachnoid hemorrhage (LR 0)
- RBC > 10,000/mm³ in final tube: Significantly increased likelihood of subarachnoid hemorrhage (LR 6.3)
- RBC between 100-10,000/mm³: Moderate likelihood (LR 1.6)
Percent change in RBC count between tubes is more useful than simple differential count 1
63% reduction in RBCs between first and fourth tubes suggests traumatic tap
- <63% reduction increases likelihood of true subarachnoid hemorrhage
Caution: "Clearing" of RBCs between tubes does not definitively rule out subarachnoid hemorrhage 2
- Even with 25% reduction in RBCs between tubes, aneurysmal bleeding can still be present
- 25% of patients with aneurysms demonstrated clearing between tubes
Additional Diagnostic Considerations
In suspected meningitis with bloody tap, correct the WBC count using this formula 3:
- True CSF WBC = actual CSF WBC - (WBC in blood × RBC in CSF)/RBC in blood
For traumatic taps, subtract 1 white cell for every 700 RBCs in the CSF 3
Prevention of Traumatic Taps
Technical Considerations
Needle selection: Using atraumatic (pencil-point) needles significantly reduces traumatic taps 4
- Odds ratio for non-traumatic tap with atraumatic needle: 2.5
- Consider smaller gauge needles (25G vs 22G) which can reduce traumatic taps by ~50% 5
Procedural factors:
- First-attempt success is associated with non-traumatic taps (OR 2.8) 4
- Minimize repositioning of needle once inserted
- Patient positioning may impact results (sitting vs. lying)
Pre-Procedure Assessment
Platelet Count Requirements
For diagnostic lumbar puncture 3:
- Maintain platelet count ≥50,000/μL before procedure
- Consider platelet transfusion if count <50,000/μL
- This threshold is intended for simple diagnostic or therapeutic LPs only
For patients with coagulopathy 3:
- LP may be harmful in patients with coagulopathy due to risk of subarachnoid hemorrhage or development of spinal subdural/epidural hematomas
- Standard recommendation is to perform LP only when patient has no coagulopathy and platelet count ≥100,000/μL
- Some guidelines suggest platelet counts ≥20,000/μL may be acceptable
- A rapidly falling platelet count is also a contraindication
Other Contraindications to LP
- Local skin infection at puncture site
- Clinically unstable patient (circulatory shock or respiratory insufficiency)
- Clinical suspicion of spinal cord compression
- Signs of increased intracranial pressure (obtain CT first) 3
Clinical Implications of RBCs in CSF
For Suspected Meningitis
- HSV encephalitis can be hemorrhagic, with elevated CSF RBC count in approximately 50% of cases 3
- CSF lactate <2 mmol/L helps rule out bacterial disease 3
- In viral meningitis, RBCs may be present but typically with lymphocytic pleocytosis
For Suspected Subarachnoid Hemorrhage
- When CT is negative but clinical suspicion remains high, LP is indicated
- Xanthochromia (yellow discoloration of supernatant after centrifugation) is more specific for true subarachnoid hemorrhage than RBC count alone
Pitfalls to Avoid
- Assuming that "clearing" between tubes definitively rules out subarachnoid hemorrhage
- Failing to correct WBC count in bloody samples when evaluating for infection
- Performing LP without checking for contraindications such as coagulopathy or low platelet count
- Delaying appropriate imaging studies when subarachnoid hemorrhage is suspected
By carefully interpreting RBCs in CSF and following these guidelines, clinicians can more accurately diagnose the underlying condition and provide appropriate management.