In 33 paired residual sera, Freelite produced significantly higher free-kappa values than N-Latex, while lambda did not differ significantly. Correlations were strong (rho 0.897 and 0.951), but Passing-Bablok analysis showed proportional kappa bias and Bland-Altman limits widened at extreme concentrations. Using assay-specific reference intervals, kappa/lambda classification agreed in 30 of 33 samples (91%; kappa 0.79). Numerical results are therefore not directly interchangeable.
Key findings
- Freelite gave higher kappa values, especially at high concentrations. • Strong correlation did not imply numerical interchangeability. • Assay-specific categorical interpretation agreed in 91%.
Why this matters globally
The work informs laboratory platform transitions: longitudinal monitoring should preserve method continuity or explicitly manage and communicate the change.
Thai researcher contribution
Maharaj Nakorn Chiang Mai Hospital and Chiang Mai University evaluate a practical implementation issue in plasma-cell disorder testing.
Limitations to consider
Only 33 archived paired samples were used, with limited extreme values; larger patient-based studies across the measurement range are needed.