Reduction ratios (RRs) and predialysis serum levels were measured for β2-microglobulin (B2M), free κ and λ light chains (FLC), prolactin (PRL), interleukin-6 (IL-6), albumin, and urea after HF-HD and at one, three, and six months of HDx. Here, B2M is linked to hydrops fetalis.