Chapter 30

Measurement of polyclonal sFLCs provides an indication of total immunoglobulin synthesis that may serve as a biomarker of immune stimulation and inflammation (Chapter 35) [683].

In a number of autoimmune diseases, the concentrations of polyclonal sFLCs correlate with disease activity. These include systemic lupus erythematosus (SLE; Section 35.4.1), Sjögren’s syndrome (Section 35.4.2), and rheumatoid arthritis (RA; Section 35.4.3). Patients at risk of disease flare could be monitored with sFLCs, to allow early intervention and possibly reduce end-organ damage and mortality. Increased concentrations of polyclonal sFLCs have also been described in a number of inflammatory diseases. These include pneumonitis (Section 35.8.1), rhinosinusitis (Section 35.7), IgG4-related disease (Section 35.8.5), viral infections e.g. hepatitis C virus (Section 35.8.2), and HIV (Section 35.6).

Hutchison and Landgren [683] speculated that sFLC measurement might complement the use of C-reactive protein (CRP) assays as a biomarker of inflammation. First, however, they suggested that a better understanding of the intra-patient variation in FLC measurements is required (Section 7.2.6), alongside knowledge of whether it is advantageous to correct sFLC measurements for renal clearance or use unmodified measurements (Section 6.3).