|Normal adult serum||Mean||Median||95% reference range||100% diagnostic range|
3.3 - 19.4
5.7 - 26.3
κ/λ sFLC ratio
0.3 - 1.2
0.26 - 1.65
Table 6.1. Mean/median values and ranges for FLC concentrations and κ/λ sFLC ratios in the sera of 282 normal individuals .
|Age (years)||κ sFLC (mg/L)||λ sFLC (mg/L)||κ/λ sFLC ratio|
|20 - 29||6.3||12.4||0.49|
|30 - 39||7.2||13.6||0.55|
|40 - 49||7.5||12.8||0.58|
|50 - 59||6.4||11.3||0.59|
|60 - 69||6.9||11.8||0.70|
|70 - 79||8.0||11.9||0.65|
|80 - 90||9.1||15.1||0.64|
Table 6.2. Median values for sFLCs and κ/λ ratios in different age groups .
The normal ranges published by Katzmann et al. were very similar to those previously reported by Bradwell et al., who observed a mean κ/λ sFLC ratio of 0.6 and a 95% reference range of 0.35 - 1.0 . Slightly lower κ and λ sFLC concentrations (95% reference ranges of 4.2 - 13.1 mg/L and 9.2 - 22.7 mg/L, respectively) observed in the Bradwell study may be attributed to a younger study population (17 - 71 years).
6.1.1. Ethnic influences
The Freelite normal ranges published by Katzmann et al. were established in an American, predominantly white, population . 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. . 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 . 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) .
A multi-centre Indian normal range study  reported slightly higher concentrations of κ and λ sFLCs compared with those reported by Katzmann et al.  (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 . 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).