CSF Protein Calculator

How does the CSF protein calculator work?

This health tool corrects the amount of cerebrospinal proteins in the case of blood contaminated CSF samples, an occurrence during traumatic lumbar punctures, usually in pediatric patients.

There are 5 fields that need to be completed, 2 referring to protein levels and the other 3 to red blood cells properties.

■ CSF protein – measured by most labs in mg/dL, the user can also input it in g/dL or g/L. The amount of protein in the cerebrospinal fluid is determined most commonly after lumbar puncture (spinal tap), but cisternal or ventricular punctures are also used.

CSF protein offers information in the diagnosis of infection, malignancy, nerve cells inflammation and other conditions.

Normal range is between 15 and 60 mg/dL and abnormally elevated results may suggest a condition affecting the central nervous system. Low values may indicate the rapid production of spinal fluid which decreases the concentration of proteins.

■ Serum protein – measured in g/dL, also available to input in mg/dL or g/L. Normal values range between 6.4 and 8.3 g/dL or 64 and 83 g/L.

■ Hematocrit – represents the volume of red blood cells to the total volume of blood, most commonly presented as percentage. Normal range is between 37 and 52%.

■ CSF red blood cells – amount of RBCs in the “bloody tap” sample in number per mm³ or mil/mm³. The amount varies, depending on the severity of the traumatic LP.

■ Blood red blood cells – RBC count from the complete blood count test in number per mm³ or mil/mm³. Normal range is 4.7 mil to 6.1 mil /mm3

The formula used for protein correction in the CSF protein calculator 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.

Cerebrospinal fluid protein concentration

CSF protein tests are usually ordered when there is suspicion of a condition affecting the SNC, of an infectious disease such as meningitis or of bleeding in the spinal fluid.

The normal range is between 15 and 60 mg/dL and sometimes the end values depend on the laboratory.

Elevated protein in CSF may indicate one of the following amongst other conditions:

■ Aseptic or bacterial meningitis;

■ Brain abscess;

■ Brain tumor;

■ Multiple sclerosis;

■ Epilepsy;

■ Acute alcoholism;

■ Neurosyphilis.

Low CSF protein is indicative of either a leak of cerebrospinal fluid or of extra production of fluid which depletes the proteins.

With as many as 30% of lumbar punctures performed on pediatric patients being traumatic and leading to a probe of blood contaminated CSF, there have been several studies which looked at the importance of finding a correction factor to support the accurate interpretation of the traumatic LP CSF protein levels.

The introduction of the peripheral red blood cells RBCs (caused by the bleeding into the subarachnoid space) increases the protein concentration and can potentially complicate diagnosis. One of the findings was that children who underwent traumatic LPs were significantly more likely to be admitted compared to those with non-traumatic lumbar punctures.

One of the rules implies the subtraction of 1.1 mg/dL of CSF protein for every 1000 cell increase in red blood cells in the cerebrospinal fluid.

References

1) Jurado R, Walker HK. (1990) Chapter 74. Cerebrospinal Fluid in Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition.

2) Majed B, Zephir H, Pichonnier-Cassagne V, Yazdanpanah Y, Lestavel P, Valette P, Vermersch P. (2009) Lumbar punctures: use and diagnostic efficiency in emergency medical departments. Int J Emerg Med; 2(4): 227–235.

3) Bruder Stapleton F (2011) Correction Factor for CSF Protein Levels in Traumatic Lumbar Puncture.

4) Nigrovic LE, Shah SS, Neuman MI. (2011) Correction of cerebrospinal fluid protein for the presence of red blood cells in children with a traumatic lumbar puncture. J Pediatr; 159(1):158-9.

5) Mazor SS, McNulty JE, Roosevelt GE. (2003) Interpretation of Traumatic Lumbar Punctures: Who Can Go Home? Pediatrics; 111 (3).

6) Doherty CM, Forbes RB. (2014) Diagnostic Lumbar Puncture? Ulster Med J; 83(2): 93–102.