From the Guidelines
To correct for a traumatic tap when analyzing cerebrospinal fluid (CSF), subtract 1 white cell for every 700 red blood cells present in the CSF, as this is the standard approximation that will suffice in most circumstances 1. This method adjusts the white blood cell count in CSF by accounting for the contamination from peripheral blood during the traumatic tap.
- The correction for protein can be approximated by subtracting 0.1 g/dl protein for every 100 red blood cells in the CSF, as suggested by some studies 1.
- However, it's essential to note that these corrections are estimates, and clinical judgment remains crucial in interpreting CSF results.
- The presence of xanthochromia (yellowish CSF) suggests true subarachnoid hemorrhage rather than traumatic tap, as this discoloration takes hours to develop and wouldn't appear in a fresh traumatic tap.
- Always collect CSF in sequential tubes, as the first tube typically contains the most blood contamination while later tubes may be clearer.
- It's also important to consider the clinical context and other CSF parameters, such as glucose ratio and protein levels, to distinguish between different conditions, including viral and bacterial infections 1.
From the Research
Correction for Cerebrospinal Fluid (CSF) Analysis
To correct for cerebrospinal fluid (CSF) analysis in cases of traumatic tap, several methods can be employed:
- Determining the cerebrospinal fluid lactate dehydrogenase level, which can effectively differentiate subarachnoid hemorrhage (SAH) from traumatic tap in LP samples 2
- Using the ratio of white blood cells to red blood cells in peripheral blood to adjust the white blood cell count found in the bloody cerebrospinal fluid, although this method may not always be reliable 3
- Analyzing the changes in percentage of hemolysis and in lactate concentrations in CSF within the first twenty-four hours following induced SAH, which can help differentiate between traumatic tap and SAH 4
- Employing a multivariable approach using CSF parameters such as red blood cell count, white blood cell count, total protein, CSF color, and supernatant to distinguish between SAH and traumatic LP 5
- Utilizing spectrophotometric analysis of the CSF, which is a reliable method of distinguishing between traumatic tap and SAH 6
Key Findings
Some key findings from the studies include:
- A significant level of cerebrospinal fluid lactate dehydrogenase to differentiate SAH from traumatic LP was estimated to be 185 2
- The presence of more than 10 times the number of white blood cells than allowed by the adjustment is a sensitive and specific indicator of meningitis 3
- The optimal cut-point of RBCadjusted was > 3667/µl to identify SAH patients with a 97% sensitivity and 94% specificity 5
- Combined CSF RBC count and CSF supernatant reliably distinguished traumatic LP from SAH 5
CSF Parameters
The following CSF parameters can be used to differentiate between SAH and traumatic LP: