Anemia is the most common issue affecting red blood cells in MCAS patients. It can be macrocytic (big cells), normocytic (normal size), or microcytic. Usually mild to moderate, but occasionally the diagnosis is mistaken for pure red cell aplasia on bone marrow examination. When macrocytosis is predominant, BMB must be performed to rule out myelodysplastic syndrome (MDS.)
Cobalamin deficiency is common, even when pernicious anemia is ruled out. Copper deficiency is sometimes the cause for microcytic anemia, although in MCAS, it sometimes causes normocytic or macrocytic anemia. This may be caused by absorption, but is also a side effect of overdose of zinc, a common ingredient in over the counter medications taken by MCAS patients to reduce symptoms. Folate deficiency is less frequently found in MCAS and is often due to hemolysis from an acquired condition like acquired chronic autoimmune hemolytic anemia, sometimes found to occur secondary to mast cell disease. Other hemolytic conditions, like paroxysmal nocturnal hematouria, should be ruled out.
Many MCAS patients have selective iron malabsorption, which sometimes resolves with antihistamine treatment. GI bleeds must be excluded. Oral iron absorption tests can be done to test iron malabsorption. A recent procedure calls for a blood sample to establish baseline plasma iron, administration of 100mg dose of oral sodium ferrous citrate, and another blood sample to test plasma iron two hours later. Increase of less than 50 ug/dl is considered evidence of malabsorption.
Iron malabsorption can happen for several reasons in the context of MCAS. Iron deficiency can be from MCAS immune dysfunction that leads to generation of antibodies against the acid secreting cells of the stomach. When the concentration of stomach acid is too low (achlorhydria), the absorption of non heme dietary iron is dramatically reduced. H2 antihistamines and PPI medications can interfere with iron absorpotion. Hepcidin, the production of which is stimulated by mast cell mediators like IL-6 and TNFa, slows down the rate with which GI cells transfer the iron into the blood stream for use.
MCAS patients sometimes exhibit low serum iron and ferritin, but have normal MCV and RCDW, which indicates no deficiency is present. This profile is thought to allude to correct transport of iron to the blood stream but poor utilization in the bone marrow.
Afrin, Lawrence B. Presentation, diagnosis and management of mast cell activation syndrome. 2013. Mast cells.
Kobune M, et al. Establishment of a simple test for iron absorption from the gastrointestinal tract. Int. J. hematol. 2011; 93:715-719.
Hitchinson C, et al. Proton pump inhibitors suppress absorption of dietary non-haem iron in hereditary hemochromatosis. Gut 2007 Sep; 56(9):1291-1295.