As Dr. Lewis says, there are Eos and Eos…
In Marc E. Rothenberg’s Review entitled: “Eosinophilia” (N Engl J Med 1998; 338:1592-1600), Dr. Rothenberg notes that Eos should normally only be about 1-3 % of leukocytes and that, in fact, eosinophilia can be dvidied into mild (351-1500c/mm3), moderate (1500-5kc/mm3) and severe (>5kc/mm3). The most common cause worldwide of eosinophilia is reported to be helminthic infection while in the first world we usually think of atopic reactions and asthma.
Don’t forget that very high numbers of eos (greater than 15-20k) is more likely to be associated with malignancy.
We discussed the NAACP mnemonic:
C: Collagen Vascular Disease
It was also noted that many infections, not just helminths can cause eosinophilia such as: Cocci, HIV, and HTLV-1.
Aaaaand, Peter recommended this great NEJM interactive case which looks at eosinophilia: