Parameters:
(1) serum kappa and lambda light chain concentrations in mg/L
(2) CSF kappa and lambda light chain concentrations in mg/L
(3) serum albumin in mg/L (1000 times value in g/L)
(4) CSF albumin by nephelometry in mg/L
free light chain index =
= (CSF free light chains in mg/L) * (serum albumin in mg/L) / ((serum free light chains in mg/L) * (CSF albumin in mg/L))
where:
• According to Tietz's Clinical Guide to Laboratory Tests the reference range for CSF albumin by nephelometry is 100 to 300 mg/L.
• According to Tietz's Clinical Guide to Laboratory Tests the reference range for serum free light chans is 3.3 to 19.4 mg/L for kappa and 5.7 to 26.3 mg/L for lambda..
• The units for serum and CSF free light chains are specified. The units for serum and CSF albumin are not given but are presumed to be mg/L.
• If kappa light chains are too low to be measured then 0.06 mg/L is used in the calculation.
• If lambda light chains are too low to be measured then 0.08 mg/L is used in the calculation.
Interpretation:
• In normal controls the KFLC index had a mean value of 1.3.
• In normal controls the LFLC index had a mean value of 1.4.
• In patients with multiple sclerosis the KFLC index ranges from 20 to 160. Kappa light chains in the CSF were measured from 1.4 to 10 mg/L.
• In patients with multiple sclerosis the LFLC index ranges from 3 to 42.
• Neuroborreliosis gave KFLC index up to 25.
