Lumbar Punctures are commonly done in the Emergency Department and we have discussed several important issues pertaining to them in the past (Positioning, Variance of Analysis based on Age, and Neonatal HSV), but we have yet to discuss the most perplexing issue with LP’s: the interpretation of the Traumatic Lumbar Puncture.

Traumatic Lumbar Puncture

• When the LP needle “inadvertently” causes vascular bleeding, this peripheral blood can contaminate the CSF.
• This blood then can effect the CSF analysis.
• In children, the reported rates of traumatic lumbar puncture are as high as 30% (depending on definition, patient age, etc).
• Always make your first attempt your best attempt to help avoid this situation all together.

The “Bloody Tap” and Meningitis

• While lumbar punctures are performed for other reasons (ex, Subarachnoid Hemorrhage, Pseudotumor Cerebri, Multiple Sclerosis), looking for potential meningitis seems to be the most common reason to perform the LP.
• When we have concern for meningitis, antibiotics should be administered expeditiously!!

  • The Problem:

    • Antibiotics administered prior to LP, may influence the CSF culture results.
      • So whenever possible, get the LP done expeditiously also!
      • Naturally, that isn’t always possible in the ED (hard to do an LP on a child you are resuscitating… or just intubated).
    • Antibiotics administered prior to LP, do not generally influence the CSF analysis (at least for the 1st 24hrs).
      • But, if the LP was “bloody”, the addition of peripheral blood into the CSF can complicate the interpretation of the CSF analysis.

     

  • The Next Question:

    • If the LP didn’t go as smoothly as we had hoped, and now we are holding multiple tubes of bloody CSF, what can we do?
    • Well, we have traditionally “pimped” our students/residents with this question to reinforce the way to “Correct” CSF WBC.

      • 1 WBC : 500 (or 1,000) RBC

        • This one is the most often heard in the halls… likely, because it is the easiest.
        • For every 500 (or 1,000) RBCs in the CSF, you can have 1 WBC in the CSF.
        • You can simply subtract this “allowable” number of WBCs from the actual number in the CSF analysis.
        • Now you have a “corrected” WBC count that you can interpret.

      • Observed : Predicted

        • Observed CSF WBC compared to Predicted CSF WBC, with Predicted CSF WBC = CSF RBC X (blood WBC / blood RBC)
        • An Observed CSF WBC : Predicted CSF WBC equal to 1 or above is concerning for meningitis.
        • One study found O:P ratios above 10  and 24 are more specific, but less sensitive, while…
        • No cases of positive CSF cultures had CSF ratios less than 1.

      • Protein

        • With meningitis, we’d expect the protein level to be elevated… but so too would traumatic blood cause this.
        • It has been shown that CSF protein concentrations increase by approximately 1-2 mg/dL for every 1000 CSF RBCs (depending on the study).
          
        • You could then determine if you have “extra,” unaccounted for protein and use that information in other predictive strategies for meningitis.

         

  • Unfortunately…

    • These formulas actually have not proven to be reliable in ruling out meningitis.
      • Several studies have found that the application of these formulas can increase the risk of missing bacterial meningitis.
      • Adjusting the WBC count increases specificity but at the expense of sensitivity, thus, reducing false positives while increasing false negatives.
        • Increasing false negative tests for meningitis is suboptimal.
    • The formulas are particularly not helpful when evaluating neonates.
    • Bonsu found Corrected Values to add no value over the Uncorrected values in kids 1 month to 18 years.

     

  • What to do then?

    • Get the LP done expeditiously!  The CSF Culture offers the best answers.
    • Make your first attempt your best attempt to decrease the rate of traumatic lumbar puncture.
    • Don’t forget about the Gram Stain!! Still a helpful and rapid tool!
    • Believe the Observed CSF WBCs.
      • Bonadio found “in children greater than 1 month of age, CSF abnormalities associated with bacterial meningitis are rarely obscured by blood contamination from traumatic lumbar puncture.”
    • Be conservative: the poor reliability of these “rules” for adjusting leukocytes in bloody-CSF leads me to be conservative.
      • Base the management on the total number of WBCs in the CSF and ignore the RBCs.
      • If there are more white cells than the normal range for age, then the safest option is to treat.
    • You can also consider adding PCR for Neisseria meningitidis, HSV and Enterovirus.

     

   

Nigrovic LE, et al. Correction of Cerebrospinal Fluid Protein for the Presence of Red Blood Cells in Children with a Traumatic Lumbar Puncture. J Pediatr 2011; 159(1): 158-159.

Greenberg RG, et al. Traumatic Lumbar Puncture in Neonates. Pediatr Infect Dis J. 2008; 27(12): 1047-1051.

Srinivasan L, et al. Traumatic Lumbar Punctures in Infants Hospitalized in the Neonatal Intensive Care Unit. Pediatr Infect Dis J. DOI: 10.1097/INF.0b013e31829862b7 Published ahead of print.

Bonsu BK, Hrper MB. Corrections for Leukocytes and PErcent of Neutrolphils Do Not Match Observations in Blood-Contaminated Cerebrospinal Fluid and Have No Value Over Uncorrected Cells for Diagnosis. Pediatr Infect Dis J. 2006; 25: 8-11.

Bonadio WA, et al. Distinguishing Cerebrospinal Fluid Abnormalities in Children with Bacterial Meningitis and Traumatic Lumbar Puncture. J Infect Dis. 1990; 162(1): 251-254.

Novak RW. Lack of Validity of Standard Corrections for White Blood Cell Counts of Blood-Contaminated Cerebrospinal Fluid in Infants. Am J Clin Pathol. 1984; 82(1): 95-97.