Comparison of the Freelite serum free light chain (SFLC) assay with serum and urine electrophoresis/immunofixation and the N Latex FLC assay.
Few reports have compared available serum free light chain (SFLC) assays. Here, a retrospective audit of the Freelite SFLC assay compared results to electrophoresis (EP)/immunofixation (IFX) and the N Latex FLC assay.A total of 244 samples collected over 3.5 months were studied using the Freelite and N Latex FLC nephelometry assays. Results were compared with serum and/or urine EP/IFX. The precision and linearity of the N Latex FLC assay was examined.Detectable paraprotein by serum or urine EP/IFX was present in 94% of samples with kappa and 100% with lambda FLC restriction. The correlation between the assays was higher for kappa (rho = 0.97) than lambda (rho = 0.89) especially when lambda results were above the upper limit of normal (rho = 0.62). Agreement in the categorical diagnosis as measured by the Cohen's kappa statistic was good (0.70). The N Latex FLC assay displayed good precision and linearity. In discordant samples the Freelite and N Latex FLC assays had equivalent agreement with IFX.Traditional methods of EP/IFX detected paraproteins in the majority of cases. Correlation between the Freelite and N Latex FLC assay is better for kappa than lambda FLC. The two assays are not entirely equivalent. Care should be taken by interpreting physicians and laboratories considering switching assays.
1Immunopathology Laboratory, SydPath, St Vincent's Hospital, Sydney 2The Kirby Institute, UNSW 3Immunology Laboratory, Royal Prince Alfred Hospital 4St Vincent's Centre for Applied Medical Research, St Vincent's Hospital 5The Garvan Institute 6St Vincent's Clinical School, UNSW, Sydney, Australia.
S C
SC
Sasson
K
K
McGill
L
L
Wienholt
A
A
Carr
D A
DA
Brown
A D
AD
Kelleher
S N
SN
Breit
W A
WA
Sewell
D000368:Aged; D004586:Electrophoresis / Q000379:methods*; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods*; D007147:Immunoglobulin Light Chains / Q000097:blood* / Q000652:urine*; D007840:Latex; D008297:Male; D008875:Middle Aged; D010265:Paraproteinemias / Q000175:diagnosis*; D015203:Reproducibility of Results; D012189:Retrospective Studies
D007147:Immunoglobulin Light Chains; D007840:Latex