3.5.1. Half-life of sFLCs

Chapter 3

sFLCs are rapidly cleared and metabolised by the kidneys. At around 25 kDa in size, monomeric FLCs, characteristically κ, are cleared in 2 - 4 hours at 40% of the glomerular filtration rate. Dimeric FLCs of around 50 kDa, typically λ, are cleared in 3 - 6 hours at 20% of the glomerular filtration rate (Figure 3.10), while larger polymers are cleared more slowly [93][94]. In contrast, IgG has a half-life of approximately 21 days with minimal renal clearance (Section 5.3). Although κ FLC production rates are estimated to be twice that of λ, their faster removal ensures that actual serum concentrations are approximately 50% lower (Chapter 5). The half-life of FLCs is dependent upon kidney function, so that FLC removal may be prolonged to 2 - 3 days in MM patients with complete renal failure [93][94][91][95]. In patients with chronic kidney disease (CKD), κ and λ sFLC concentrations increase due to reduced renal clearance [96]. When renal clearance is reduced, a greater proportion of sFLC are removed through pinocytosis by cells of the reticuloendothelial system [97]. This mechanism removes κ and λ sFLC at the same rate so the relative FLC concentrations change to reflect more closely the higher rate of κ production and there are minor increases in the κ/λ sFLC ratio [96].