Pitfalls of reverse epidemiology, the less than perfect association of reduced plasma β2M with survival, study limitations and finally the disparate effects of plasma β2M in patients with hypoalbuminemia suggest that additional biomarkers are needed to both understand the effects of HF dialysis on clinical outcomes and provide a causal explanation about the role of β2M in mediating these outcomes. The gene discussed is B2M; the disease is hydrops fetalis.