Immunoglobulin E (IgE) is a type of antibody (or immunoglobulin (Ig)"isotype") that has only been found in mammals. IgE is synthesised by plasma cells. IgE's main function is immunity to parasites such as helminths like Schistosoma mansoni, Trichinella spiralis, and Fasciola hepatica. Total IgE is utilized during immune defense against certain protozoan parasites such as Plasmodium falciparum. Total IgE may have evolved as a last line of defense to protect against venoms.

25（OH）-D is a prehormone that is produced in the liver by hydroxylation of vitamin D3 (cholecalciferol) by the enzyme cholecalciferol 25-hydroxylase. Physicians worldwide measure this metabolite to determine a patient's vitamin D status.

Ferr is a universal intracellular protein that stores iron and releases it in a controlled fashion. The protein is produced by almost all living organisms, including algae, bacteria, higher plants, and animals. In humans, it acts as a buffer against iron deficiency and iron overload. Ferritin is found in most tissues as a cytosolic protein, but small amounts are secreted into the serum functioning as an iron carrier. Plasma ferritin is also an indirect marker of the total amount of iron stored in the body. Hence serum ferritin is used as a diagnostic test for iron-deficiency anemia.