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.
References:
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.
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