Corrected CSF Protein for Blood Contaminated CSF
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CSF Protein (Measured) (mg/dL)
Serum Protein (Measured) (gram/dL)
Hematocrit (%)
CSF RBC's (Measured) (/mm^3 )
Blood RBC's (x 10^6/mm^3)
R e s u l t s
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Corrected CSF Protein (mg/dL)
 
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Corrected CSF Protein for Blood Contaminated CSF

When performing a Lumbar Puncture (LP) to obtain Cerebrospinal Fluid (CSF); it is not uncommon for some peripheral blood to mix with (contaminate) the CSF that is obtained.

In such cases, the actual protein level in the CSF can be corrected by factoring in the effect of contamination and deducting the quantity of protein present is due to contamination with peripheral blood.

The formula to correct for this is:

Corrected Protein in CSF = Measured Protein CSF - [SProt * 1000 * (100 - Hct / 100) * CSFRBC / BRBC]

Corrected and Measured Protein in CSF are both in mg/dL
SProt = Serum protein in grams/dL
Hct = Hematocrit in %
CSFRBC = RBC-s found in CSF/mm 3
BRBC = RBC-s in peripheral blood in cells/mm 3

As an example to demonstrate implementation of this formula, a patient has the following:

  • CSF protein is reported as 30 mg/dL
  • Serum protein is 8.0 grams/dL
  • Hematocrit is 38%
  • RBCs in CSF are 5,000 RBC's/mm 3
  • Blood RBCs are 4.0 million cells/mm 3

In the example above, the math is:

Corrected Protein = 30-[8 * 1000 * (100 - 38/100) * 5,000/4,000,000] = 23.8 mg/dL

Reference:
Cerebrospinal Fluid. In: Strasinger SK, Di Lorenzo MS. Urinalysis and Body Fluids. 5th ed. Philadelphia, PA: E. A. Davis Company; 2008:177-198.