Decreased levels of basophils in the blood may be caused by an acute infection, cancer or a severe injury, according to MedlinePlus. The normal range of basophils in the blood, as a percentage of all types of white blood cells, is between 0.5 and 1 percent.
Some conditions may affect test results. Ovulation, pregnancy and hyperthyroidism may decease basophil levels even further than normal, according to Vanderbilt University. Absolute values of basophils in the blood normally range from 190 cells per microliter of blood in adults to 200 cells per microliter of blood in children.
Tests to evaluate basophils are done to determine if a patient has an allergy, chronic myeloid leukemia, a parasitic infection or myelodysplastic syndrome. Increased levels of basophils indicate ulcerative colitis, hypothyroidism, nephrosis or someone who just had their spleen surgically removed, notes Vanderbilt University.
Basophils are one of five types of white blood cells measured in a blood differential test. Relative values of basophils are described as a percentage of overall white blood cells as compared to the rest of white blood cells. Basophils are one of the lowest types of white blood cells in normal counts, notes MedlinePlus. A blood differential test measures neutrophils, lymphocytes, monocytes, eosinophils and basophils. Neutrophils and lymphocytes are the two most common types of white blood cells in the human body.