Basophils make up the smallest fraction of white blood cells circulating in the blood (about 1%). They are associated with allergic response, for example. The analysis tells the number of basophils per litre of blood (basophil #) and the proportion of white blood cells represented by basophils (basophil ratio). Results must be interpreted in light of clinical observations, other results from the current blood count, and variations in results over time.
An increase in the basophil count or ratio (basophilia) is associated with certain rare allergic reactions (bees, food), inflammatory conditions (rheumatoid arthritis, ulcerative colitis, etc.) and some forms of leukemia (chronic myeloid leukemia).
A decrease in the basophil count or ratio is generally of no clinical significance.