Table 1. Cut-offs for predicting positive o-fLC test (≥2 CSF-restricted bands) suggested by receiver operating characteristic curve analysis.
| Free kappa light chains | n (o-fKLC+/ o-fKLC-) | CSF fKLC (mg/l) | fKLC quotient (∙103) | fKLC index |
| Freelite™ on SPAPLUS | 70/89 (70/87 for fKLC quotient and index) | >0.54 (82.9; 97.8) | >30.61 (84.3; 98.9) | >3.25 (90.0; 82.8) |
| N Latex FLC™ on BN ProSpec | 20/29 | >0.417 (85.0; 100) | >17.60 (90.0; 96.6) | >3.21 (80.0; 100) |
| ELISA (BioVendor) | 22/16 | >0.025 (90.9; 87.5) | >9.09 (81.8; 93.8) | >1.20 (77.3;87.5) |
| ELISA (in-house, monoclonal standards) | 49/84 (46/82 for fKLC quotient and index) | >0.216 (87.8; 90.5) | >19.18 (89.1; 95.1) | >2.75 (84.8; 96.3) |
| ELISA (in-house, Freelite™ standards) | 56/85 | >0.340 (85.7; 94.1) | >17.48 (89.3; 96.5) | >2.17 (89.3; 89.4) |
| Free lambda light chains | n (o-fLLC+/ o- fLLC-) | CSF fLLC (mg/l) | fLLC quotient (∙103) | fLLC index |
| Freelite™ on SPAPLUS | 49/110 (49/109 for fLLC quotient and index) | >0.30 (98.0; 91.8) | >36.31 (91.8; 99.1) | >6.68 (79.6; 97.3) |
| N Latex FLC™ on BN ProSpec | 15/33 | >0.368 (93.3; 87.9) | >16.92 (100; 90.9) | >3.82 (86.7; 100) |
| ELISA (BioVendor) | 17/21 | >0.039 (94.1; 90.5) | >7.38 (82.4; 95.2) | >0.92 (82.4;80) |
| ELISA (in-house, monoclonal standards) | 40/102 | >0.358 (87.5; 91.2) | >22.05 (77.5; 96.1) | >3.03 (75.0; 91.2) |
| ELISA (in-house, Freelite™ standards) | 40/102 | >0.272 (92.5; 85.3) | >21.11 (80.0; 92.2) | >2.88 (77.5; 90.2) |
n, number of positive/negative cases; o-, oligoclonal; fKLC, free kappa light chains; fLLC, free lambda light chains. Sensitivity and specificity obtained by receiver operating characteristic analysis are given in parentheses. All areas under the curve were above 0.9 except for fKLC index using BioVendor ELISA and fLLC index using BioVendor ELISA as well as in-house ELISAs (all these areas under the curve were 0.87). At pairwise comparison of other assays against the Freelite™ assay, in-house ELISAs for CSF fLLC and fLLC quotient performed somewhat worse (P = 0.0167–0.0434); all other differences between the areas under the curve were not significant (P > 0.05).