For a particular Hevylite isotype, both κ and λ assays (e.g. IgAκ and IgAλ) should always be measured, and the HLC ratio calculated (e.g. IgAκ/IgAλ). Definitions of commonly used terms are given in Table 11.5. For serial measurements, either the iHLC, dHLC or the HLC ratio may be used [38][37][238][929]. When an abnormal HLC ratio is present, and the concentration of the uninvolved HLC-pair is below the normal reference interval, this is termed “HLC pair suppression”.

Term Definition Comment For an IgGκ MM tumour...
iHLC Involved HLC The HLC isotype that is produced by the tumour.
uHLC Uninvolved HLC The same heavy chain isotype but alternate light chain type to the iHLC. IgGλ
HLC ratio e.g. IgGκ/IgGλ For a particular immunoglobulin isotype, a ratio of the concentration of Hevylite κ to λ. Indicates monoclonality. IgGκ/IgGλ
dHLC iHLC - uHLC For a particular immunoglobulin isotype, the difference in concentration between iHLC and uHLC. IgGκ - IgGλ
HLC pair suppression When the concentration of the uHLC is below the normal reference interval
The HLC ratio must be abnormal.Suppression of IgGλ

Table 11.5. Summary of HLC terminology.