68974-5

LOINC code 68974-5 identifies "IgG.intrathecally synthesized/IgG.total in Cerebral spinal fluid". Note that both the numerator and denominator are concentration of the same protein in the CSF, ..BUT the denominator is the total CSF concentration and the numerator is the contribution of the protein in the CSF that is MADE IN THE CSF (i.e. "intrathecally") ---as opposed to protein that has diffused in from the blood. The calculation is IgX(Intracthecal fraction) = [IgX(Intrathecally synthsized concentration)/IgX(Total CSF Concentration)]*100 from "Multiple Sclerosis (1998) 4, 111 - 117" From the same paper, the "IgX(Intrathecally synthsized concentration)" is complex to determine, but is based on the amount of protein in the CSF over and above that of the normal upper limit expected in the CSF (compared to that in blood). That 'over and above' amount is what is deemed to be produced in the CSF, which is the "Intrathecal Fraction"...... Same theme repeats in other papers (e.g. Am. J. Trop. Med. Hyg., 82(6), 2010, pp. 1094-1098)

This code measures IgG.intrathecally synthesized/IgG.total in CSF. It belongs to the CHEM class in the LOINC classification.

LOINC (Logical Observation Identifiers Names and Codes) is a universal standard for identifying laboratory and clinical observations. It is maintained by the Regenstrief Institute and used worldwide for health data exchange.