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Chapter 6

The Freelite normal ranges published by Katzmann et al. were established in an American, predominantly white, population [644]. Known ethnic differences in the normal ranges of total immunoglobulins (Chapter 10) have prompted a number of laboratories to determine normal sFLC ranges for their local populations.

European research groups have reported Freelite reference ranges for normal individuals that are comparable to Katzmann et al. [156][157]. Similarly, sFLC concentrations in a small South African cohort including Black (57/113), mixed-race (44/113) and Caucasian (12/113) subjects were not significantly different, both for the local population as a whole, and for the Black and mixed-race populations independently [158]. In a Han Chinese population of 326 subjects, although a narrower κ/λ sFLC ratio normal range was observed (0.32 - 1.52), this local range and the Katzmann range (0.26 - 1.65) provided the same diagnostic sensitivity and specificity for multiple myeloma (MM) (area under ROC curve 0.99 in both cases) [159].

A multi-centre Indian normal range study [900] reported slightly higher concentrations of κ and λ sFLCs compared with those reported by Katzmann et al. [644] (both p<0.01). The concentration of κ sFLCs was slightly higher than that of λ sFLCs, and consequently the κ/λ sFLC ratio (0.36 – 2.33, 95% range) was also higher than that reported by the American study [644]. The authors suggest that their findings are consistent with the lower glomerular filtration rates of normal Indian subjects than those of Western populations (Section 6.3).