Biological variation of immunoglobulin heavy chain-light chain pairs in serum

Background: Assays for immunoglobulin heavy chain-light chain (HLC) pairs called Hevylite® have recently been developed. These assays can be useful in patients with hard to interpret serum protein electrophoresis peaks. Measurement of the biological variation of clinical laboratory tests can help clinicians better interpret laboratory results.

Methods: Serum samples were collected from 15 healthy donors and assayed with IgAκ, IgAλ, IgGκ and IgGλ Hevylite. The coefficients of the within-subject and between-subject biological variation, index of individuality (II), number of samples (n) required to determine the homeostatic setting points (HSP) and reference change values (RCV) were calculated.

Results: The coefficients of the within-subject biologic variation were all less than the between-subject biological variation. The II for all the assays and their κ/λ ratios were near or <0.6. The RCV ranged from 17 to 41%. The number of measurements to determine the HSP for an individual was 1 for the HLC ratios and between 2 and 9 for the individual isoforms.

Conclusions: II indicates it is better to use the patient's individual results rather than population based reference values, fewer measurements are required to determine the HSP for the HLC ratios than the individual isoforms and the RCV can now be used to aid in interpretation.