CSF Lactate Dehydrogenase for Distinguishing Subarachnoid Hemorrhage from Traumatic Lumbar Puncture
Lumbar puncture is performed for many indications including the diagnosis of:
- Meningitis, encephalitis, syphilis, abscess
- Subarachnoid hemorrhage, intracerebral hemorrhage, subdural hematoma
- Multiple sclerosis
- Acute leukemia or lymphoma with CNS involvement
- Spinal cord tumor
Traumatic taps are fairly common, occurring with an estimated frequency of 10 to 20%. The most common practice to distinguish a subarachnoid hemorrhage from a traumatic tap is to perform a RBC count on the first and last CSF tubes collected. CSF samples from a traumatic tap generally show clearing of RBCS with successive tubes, whereas those from a true hemorrhage show a more stable RBC count.
Other CSF findings are also helpful in distinguishing traumatic tap from subarachnoid hemorrhage. A CSF RBC count of greater than 10,000 favors a diagnosis of subarachnoid hemorrhage. The presence of xanthochromia, which is a yellowish brown color that results from RBC hemolysis and hemoglobin degradation, is suggestive of subarachnoid hemorrhage. The presence of erythrophagocytosis and hemosiderin-laden macrophages are indicative of subrarachnoid hemorrhage as long as there has not been a prior traumatic tap.
A recent cross-sectional observational study evaluated the ability of CSF lactate dehydrogenase (LDH) to distinguish between traumatic tap and subarachnoid hemorrhage. Fifty-two patients with a diagnostic suspicion of subarachnoid hemorrhage were enrolled in the study. Equal numbers of patients were enrolled in two groups. Group 1 consisted of patients with subarachnoid hemorrhage confirmed by CT scan. Lumbar puncture was performed in the operating room by the neurosurgical team. Group 2 included patients who had a traumatic lumbar puncture performed in the emergency department for any other medical indication.
CSF LDH levels were higher in patients with subarachnoid hemorrhage compared to traumatic tap. ROC analysis suggested that a CSF LDH concentration of 185 U/L had a sensitivity of 81%, specificity of 96%, positive predictive value of 95% and negative predictive value of 83%. Positive likelihood ratio was 21 and negative likelihood ratio was 0.20. No patients with CSF levels greater than 210 U/L had a traumatic tap. This small study suggested that CSF LDH levels might be helpful in differentiating between SAH and traumatic tap.
Reference
Saeedi M, et al. Determining the Value of Cerebrospinal Fluid Lactate Dehydrogenase Level in Differentiating Subarachnoid Hemorrhage From Traumatic Lumbar Puncture. Arch Pathol Lab Med. 2018;142:634–637
