Use of red vacutainer for collection of CSF causes falsely high estimation of proteins by pyrogallol red method.

BACKGROUND

Though plain plastic/glass tubes are recommended for CSF collection, many laboratories use the commercially available red topped evacuated tubes for CSF collection for biochemical analysis. These red vacutainers affect the assay of some serum parameters.

AIM

We evaluated the effect of using red vacutainer for CSF collection on estimation of proteins.

METHODS

CSF samples of 50 patients were collected in plain plastic containers. One milliliter from these were transferred to red vacutainers and mixed gently. Protein by pyrogallol red method was estimated directly from plastic containers and from the sample that was poured to red vacutainers. We further prepared different concentrations of bovine serum albumin in normal saline and estimated the O.D. on a spectrophotometer and protein levels on a clinical chemistry analyzer, similarly before and after transferring 1 ml to red vacutainer.

RESULTS

The CSF protein levels were significantly higher (p=<0.0001) when transferred to a red vacutainer (median: 81.5 and range:32-324 mg/dl) than that estimated directly from a plain plastic container (Median: 50.5 and range: 20-300 mg/dl) and affected the interpretations in 50% cases. The protein levels were 25, 50, 50 and 355% higher when BSA prepared at concentrations of 100, 50, 25 and 10mg/dl respectively were transferred to red vacutainers. But for 750, 1500 and 3000 mg/dl of BSA concentrations, the increase in red vacutainer was 1.4, 2 and 0.7% respectively.

CONCLUSION

Collection of CSF in red vacutainer significantly affects CSF protein estimations, probably due to the presence of clot activator. This might alter the interpretation of result and thus management of the subject. So the red vacutainer should not be recommended for CSF collection.