From the Guidelines
In a traumatic tap, pleocytosis can be estimated using correction formulas to distinguish between true pleocytosis and blood contamination, with the most reliable approach being to subtract 1 white blood cell (WBC) from the cerebrospinal fluid (CSF) count for every 700 red blood cells (RBCs) present, as suggested by studies 1. When evaluating a traumatic tap, it is essential to consider the potential for blood contamination to affect the CSF analysis. The presence of pleocytosis, or an abnormal number of cells, can be misleading in this context.
- To accurately assess pleocytosis, clinicians can use correction formulas, such as subtracting 1 WBC for every 700 RBCs present in the CSF, as mentioned in the study 1.
- Alternatively, a ratio of 1 WBC per 500-1000 RBCs can be used, although the former method is considered more reliable.
- Collecting CSF in sequential tubes and comparing the RBC counts can also help distinguish between a traumatic tap and true subarachnoid hemorrhage, with a decreasing trend suggesting the former.
- Other indicators, such as examining the supernatant for xanthochromia (yellow discoloration), can also be helpful in determining the presence of true pathologic pleocytosis.
- The timing of the lumbar puncture is also crucial, as xanthochromia may not appear immediately after a true hemorrhage.
- It is essential to note that true pathologic pleocytosis should be suspected when the CSF WBC count exceeds what would be expected from the blood contamination alone, as indicated by the study 1.
- By using these correction methods, clinicians can avoid misdiagnosis and unnecessary treatments when blood contamination occurs during the procedure, ultimately improving patient outcomes in terms of morbidity, mortality, and quality of life.
From the Research
Significance of Pleocytosis in Traumatic Tap
The presence of an abnormal number of cells, or pleocytosis, in a traumatic tap (cerebrospinal fluid (CSF) leak due to trauma) can be significant in diagnosing various conditions.
- Pleocytosis can be caused by infection of the central nervous system (CNS), non-infectious neurological diseases, malignancy, and infection outside CNS 2.
- In children, a cutoff value of 321 white blood cells/μL in the CSF can distinguish between bacterial and non-bacterial meningitis with a sensitivity of 80.6% and specificity of 81.4% 3.
- However, in cases of traumatic lumbar puncture, the correction of CSF white blood cell count is necessary to avoid misclassification of patients with bacterial meningitis 4, 5.
- The optimal correction factor for CSF WBC counts in infants with traumatic lumbar punctures is a cerebrospinal fluid RBCs:WBCs ratio of 877:1 4.
- In adults, indicators of false pleocytosis in traumatic LP include bloodier CSF and milder pleocytosis, and correction factors can be useful in such cases 5.
Diagnostic Considerations
When interpreting CSF results in cases of traumatic tap, it is essential to consider the following:
- The presence of pleocytosis does not always indicate infection, as non-infectious conditions can also cause an abnormal number of cells in the CSF 2.
- The correction of CSF WBC counts is crucial in avoiding misclassification of patients with bacterial meningitis 4, 5.
- The choice of correction factor can affect the specificity and sensitivity of the diagnosis, and an expected specificity/sensitivity tradeoff is observed 5.