When would you suspect an allergy to the dialysis membrane in patients who complain of pruritis during dialysis?  

The short answer is no. Pruritus is so common with renal disease, and allergic reactions to dialyzers are uncommon. If the pruritus can confidently be documented to be only during dialysis and not at any other time, then it may be worth trying a different dialyzer but it would take a lot for me to b...