METHODS: Hevylite assays were done on the sera of 132 MM patients at the time of diagnosis (IgG 94, IgA 38). HLC-r was calculated in the case of i-HLC-κ from the i-HLC-κ/u-HLC-λ ratio and for i-HLC-λ from the i-HLC-λ/u-HLC-κ ratio. D-S and ISS stages were evenly distributed.
RESULTS: Md IgG-κ HLC-r was 64.8 (2.7-2222) and of IgG-λ HLC-r 49.6 (0.7-465.1), in the case of IgA-κ, Md HLC-r was 408.9 (3.4-3966) and for IgA-λ HLC-r the Md was 180.0 (0.1-3110). Normal levels of HLC pairs and HLC-r did not always rule out the diagnosis of MM. HLC-r correlated with FLC-r in IgG (r = 0.244, P = 0.018), but not in the IgA type. For IgG, HLC-r values were significantly different in patients with abnormal vs normal levels of Hb (P < 0.0001), albumin (P < 0.043), β2-M (P < 0.0001) and creatinine (P = 0.034) but not thrombocyte count, Ca or LDH. For the IgA isotype, we found a significant difference in HLC-r values only for thrombocyte count (P = 0.026) and β2-M (P = 0.016) but not for Hb, albumin, Ca, LDH or creatinine. For the IgG isotype there was a significant relationship of HLC-r index to stages 1-3 (P = 0.038) and substage A vs B (P = 0.048) according to D-S, and with high significance to stages 1-3 according to ISS (P = 0.005) and between stages 1 vs 3 (P = 0.001). For the IgA isotype, we found significant differences in HLC-r only between stages 1-3 (P = 0.025) according to D-S but not in the case of ISS. There were no significant correlations between i-HLC Ig levels and D-S or ISS stages in both IgG-κ and λ and IgA-κ and λ. Exceptions were significant differences for stages 1 vs 3 (P = 0.012) and 2 vs 3 (P = 0.017) for the IgG-λ isotype. There were no correlations of the HLC-r and u-HLC levels for either D-S or ISS stratifications in all HLC isotypes.
CONCLUSIONS: We found a significant positive contribution of HLC-r using the i-HLC/u-HLC ratio even in the case of i-HLC-λ i.e. i-HLC-λ/u-HLC-κ. Variable results for the relationship of important laboratory parameters and D-S and ISS stratifications (stage 1-3) to HLC-r values in IgG and IgA isotypes make separate interpretation of the Hevylite method results necessary in clinical practice.