title: Anaemia, microcytosis and sirolimus--is iron the missing link?
abstract: BACKGROUND
  Sirolimus (SRL) has been implicated in the causation of post-transplantation anaemia (PTA). It also induces profound red blood cell (RBC) microcytosis, which is poorly understood.
  
  
  METHODS
  We conducted a retrospective study of SRL-induced anaemia and microcytosis [mean corpuscular volume (MCV) <80 fl] with specific reference to iron homeostasis in 93 renal transplant patients treated with SRL for at least 3 months.
  
  
  RESULTS
  While mean haemoglobin (Hb) and use of erythropoiesis-stimulating agents increased on SRL, RBC MCV underwent a significant decline throughout the whole study period of 24 months (P < 0.001) with the percentage of microcytosis rising from 2.2% at the start of SRL therapy to 40.7% after 24 months of therapy. An association between dMCV (MCV change on SRL) and SRL levels was shown at 3, 6, 12 and 24 months post-SRL (P = 0.015, P = 0.037, P = 0.002 and P = 0.001, respectively). Intravenous (IV) iron administration was an independent predictor of dMCV at 12 and 24 months on SRL (P = 0.031 and P = 0.048, respectively). All patients who, after starting SRL and seeing a fall in MCV, then went on to receive IV iron therapy, showed a marked increase in MCV; this did not happen to patients given oral iron therapy.
  
  
  CONCLUSIONS
  SRL is associated with mild anaemia, but marked RBC microcytosis-these phenomena are correlated with SRL levels and the use of IV iron. Functional iron deficiency and impaired gastrointestinal absorption of iron seem likely explanations.
authors.affiliation: Department of Renal Medicine and Transplantation, Guy's and St Thomas' NHS Foundation Trust, King's Health Partners AHSC, London, UK.
authors.forename: Sofia
authors.initials: S
authors.lastname: Sofroniadou
authors.forename: Theodoros
authors.initials: T
authors.lastname: Kassimatis
authors.forename: David
authors.initials: D
authors.lastname: Goldsmith
mesh_terms: D000328:Adult; D000740:Anemia / Q000139:chemically induced* / Q000188:drug therapy; D001799:Blood Sedimentation; D004909:Erythrocyte Indices / Q000187:drug effects*; D004921:Erythropoietin / Q000627:therapeutic use; D005260:Female; D005919:Glomerular Filtration Rate / Q000187:drug effects; D006801:Humans; D007166:Immunosuppressive Agents / Q000009:adverse effects*; D007501:Iron / Q000378:metabolism* / Q000627:therapeutic use; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D020123:Sirolimus / Q000009:adverse effects*
chemical_list: D007166:Immunosuppressive Agents; D004921:Erythropoietin; D007501:Iron; D020123:Sirolimus