Complement Activation
The level of complement activation produced by a membrane is considered a significant determinant of membrane biocompatibility.

All membranes activate complement and leukocytes to some extent, but unmodified cellulose membranes are known to be the most potent activators, and are therefore considered bioincompatible.

Complement activation products include anaphylatoxins such as C3a, which may cause allergic reactions during dialysis, and can also lead to acute intradialytic pulmonary hypertension, chronic low grade systemic inflammation, and leukocyte dysfunction.

Platelet Activation
A significant amount of platelet activation can occur during hemodialysis and cause thrombosis in the dialyzer.

Plasma fibrinogen binds to the membrane, causing platelet adhesion and activation, while blood flow within the dialyzer and the extent to which air can be removed from it during priming can both impact clotting, regardless of the membranes chemical composition.

Recently, cases of thrombocytopenia have been reported with PSF membranes that have been sterilized by electron beam radiation, though the mechanism is unclear

The chemical composition of other dialyzer components such as the housing also influences biocompatibility.
Bisphenol A (BPA) in dialyzers has been the focus of investigation by the Food and Drug Administration because it has been eluted from dialyzer housing made of polycarbonate.

BPA and phthalates have been found to leach into the blood during dialysis and this is superimposed on blood levels that are already elevated because BPA excretion is reduced in renal disease.

Patients receiving dialysis with PSF membranes have displayed elevated BPA levels after treatment and thus some manufacturers have developed dialyzers that contain no BPA.

Similarly, the FDA has reported that di (2-ethylhexyl) phthalate (DEHP) may pose a health risk in medical devices such as dialyzers, and therefore some manufacturers have removed it from their products.

The potting material, which secures the hollow fibers at both ends of the dialyzer, is made of polyurethane, which has a high affinity for the sterilizing agent ethylene oxide (ETO).

When ETO accumulates in the potting material, it can diffuse into the blood and cause anaphylactic reactions.

The dialyzer housing is made of polycarbonates or other polymers that may be gas permeable and thus adsorb ETO during sterilization.

The use of ETO is now less common, having been replaced with steam and gamma radiation