Any ideas on the following would be much appreciated. We've got a 37 year old male renal transplant patient who has sickle cell anaemia. Because of this, he is having weekly red cell exchange transfusions (~4 units). He's on Tacrolimus (5 mg, twice a day) and we are currently monitoring this on samples taken prior to transfusion. These however are giving results consistently between 3-4 ug/L. Is anyone aware of poor uptake of Tacro by erythrocytes in patients with sickle cell, thus affecting whole blood concentrations? Also I would presume that his weekly transfusions will be affecting the concentrations but to what degree? His renal function appears to be fine, with creatinine concs of 110-120 umol/L