CSF Protein Correction for Blood Contamination
The standard approach is to subtract 0.1 g/dL (or 1 mg/dL) of protein for every 100 red blood cells per microliter present in the CSF sample. 1
Correction Formula
The correction formula is straightforward:
Corrected CSF Protein = Measured CSF Protein - (CSF RBC count ÷ 100) × 0.1 g/dL
Or equivalently:
Corrected CSF Protein (mg/dL) = Measured CSF Protein - (CSF RBC count ÷ 100)
This 1:100 ratio (1 mg/dL protein per 100 RBCs/μL) accounts for the protein contribution from blood contamination during lumbar puncture. 1
Clinical Application
Apply this correction when traumatic tap occurs: The presence of RBCs in CSF that are not expected from the underlying pathology (such as subarachnoid hemorrhage) requires correction to avoid overestimating true CSF protein elevation. 1
Use contemporaneous RBC counts: The correction should be based on the RBC count from the same CSF sample being analyzed for protein, as RBC counts can vary between sequential collection tubes. 2
Consider the clinical context: In conditions like subarachnoid hemorrhage where blood is pathologically present in the CSF (not from traumatic tap), elevated protein reflects true disease severity and should not be corrected using this formula. 2, 3
Important Caveats
Serial bloody specimens suggest true hemorrhage rather than procedural trauma. If multiple sequential CSF collection tubes show persistent or increasing RBC counts, this indicates pathologic bleeding (such as in subarachnoid hemorrhage or HSV encephalitis) rather than traumatic tap contamination. 1 In these cases, the elevated protein is clinically meaningful and should not be corrected.
The correction formula is a guide, not an absolute rule. Clinical judgment must incorporate other CSF parameters including glucose ratio, lactate levels, Gram stain, culture, and PCR testing to establish definitive diagnosis. 1
Blood contamination introduces proteases that may degrade CSF proteins. Research demonstrates that blood-contaminated CSF samples show less protein stability at 37°C compared to uncontaminated CSF, suggesting blood-borne proteases can induce protein degradation during and after sample acquisition. 4 This means the correction formula may not fully account for all blood-related protein alterations.
Prognostic Significance
In subarachnoid hemorrhage specifically, elevated CSF protein (even after appropriate correction for RBC contamination) independently predicts poor functional outcome and is associated with delayed cerebral infarction. 2, 3 Lower corrected CSF protein concentrations correlate with better 3-month functional outcomes and ICU survival. 3