CSF Protein Calculator
Determines the cerebrospinal protein correction for blood contaminated CSF in pediatric patients.
Purpose:
In traumatic lumbar punctures, sometimes the cerebrospinal fluid is contaminated with blood.
The CSF protein calculator applies a correction for blood contaminated CSF (basically corrects the amount of cerebrospinal proteins) in the case of pediatric trauma.
The protein correction formula is:
Protein = CSF protein – (Serum protein x 1000 x (1 – Hematocrit / 100) x CSF RBC / (Blood RBC x 1e6))
Where:
■ CSF protein is in mg/dL;
■ Serum protein is in g/dL;
■ Hematocrit is in %;
■ CSF RBC is in /mm3;
■ Blood RBC is in mil/mm3;
■ 1e6 means 1 x 106= 1,000,000.
Variables and CSF formula
As many as 30% of pediatric lumbar punctures are traumatic and result in probes of blood contaminated CSF.
The bleeding into the subarachnoid space introduces peripheral red blood cells that may potentially increase the protein concentration and lead to false results.
The correction factor helps perform an accurate interpretation of the traumatic LP cerebrospinal protein levels.
The CSF protein calculator requires the following input (2 variables referring to protein content and 3 variables referring to RBC properties):
■ CSF protein in mg/dL. The calculator allows input in g/dL or g/L;
■ Serum protein that is measured in g/dL, also input in mg/dL or g/L;
■ Hematocrit in percentage;
■ CSF red blood cells in number per mm3or mil/mm3;
■ Blood RBCs – count in number per mm3or mil/mm3.
The CSF protein is a determination that follows lumbar punctures (also known as the spinal tap), however, sometimes, cerebrospinal fluid from cisternal or ventricular punctures is used.
The amount of CSF protein can be used in diagnosis of infections, malignancy or other conditions. CSF normal range is 15 – 60 mg/dL. Abnormally elevated results are consistent with conditions affecting the central nervous system. Low CSF protein levels may be caused by a rapid production of spinal fluid.
Normal values for serum protein are between 6.4 and 8.3 g/dL or 64 and 83 g/L.
The normal range for haematocrit is between 37 and 52%. The more traumatic the spinal tap, the higher the number of blood cells in CSF.
The protein correction formula is:
Protein = CSF protein – (Serum protein x 1000 x (1 – Hematocrit / 100) x CSF RBC / (Blood RBC x 1e6))
Where:
■ CSF protein is in mg/dL;
■ Serum protein is in g/dL;
■ Hematocrit is in %;
■ CSF RBC is in /mm3;
■ Blood RBC is in mil/mm3;
■ 1e6 means 1 x 106= 1,000,000.
CSF protein concentration
Cerebrospinal fluid protein tests are routinely ordered when there is suspicion of a condition that affects the central nervous system, especially when meningitis or bleeding in the spinal fluid are suspicioned.
The normal amount of proteins in the CSF is between 15 and 60 mg/dL, with minor variation, depending on the laboratory.
Elevated CSF protein levels indicate aseptic or bacterial meningitis, brain malignancy or abscesses, epilepsy, multiple sclerosis or neurosyphilis, amongst others.
Decreased CSF protein levels suggest either a leak of cerebrospinal fluid or extra production of fluid which in turn contributes to a depletion of the proteins.
Another correction rule aimed at reducing the impact of falsely elevated protein concentrations in traumatic LP involves the subtraction of 1.1 mg/dL of CSF protein for every 1000 cell increase in red blood cells.
References
1. Jurado R, Walker HK. Cerebrospinal Fluid in Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. 1990; Chapter 74.
2. Stapleton B. F. Correction Factor for CSF Protein Levels in Traumatic Lumbar Puncture. 2011.
3. Nigrovic LE, Shah SS, Neuman MI. Correction of cerebrospinal fluid protein for the presence of red blood cells in children with a traumatic lumbar puncture. J Pediatr. 2011; 159(1):158-9.
4. Majed B, Zephir H, Pichonnier-Cassagne V, Yazdanpanah Y, Lestavel P, Valette P, Vermersch P. Lumbar punctures: use and diagnostic efficiency in emergency medical departments. Int J Emerg Med. 2009; 2(4): 227–235.
