Basophils

Of the five types of white blood cell, basophils are the smallest group: fewer than one in a hundred. Their granules stain dark blue under the microscope and are full of histamine and heparin. In an allergic reaction they recognise the allergen through antibodies on their surface, and release the histamine that widens the vessels, makes the nose run and the skin itch. They are the travelling relatives of the mast cells, which do the same from the tissue. Because there are so few, the count in your blood is coarse: the lab counts only a handful in an ordinary measurement, and the difference between zero and a few hundredths is measurement noise. Every band starts at zero, and that means a low count is never a finding. The count rises slightly with allergy, with an inflammation that has been running longer, such as a bowel inflammation, and with an underactive thyroid. Cortisol and prednisone suppress it, as with the eosinophils. Your report shows the count in ×10⁹/L. Normal is about 0 to 0.15 ×10⁹/L, where the labs overlap. Only a count that persistently sits far above the band is taken seriously, because that is the classic picture of a bone marrow disease in which the production of white cells goes astray.

On their own basophils say little, and that is the honest message of this page. They are so scarce that an ordinary measurement can hardly tell normal from slightly raised, and most rises are a mild response to something you already know: an allergy, an inflammation that is running. Anyone reading their blood count and seeing a slightly raised basophil count may usually leave it alone. Where they do add something is in the pattern. With an allergy the eosinophils rise and the basophils sometimes along, while CRP stays normal. With an inflammation that has been running a while the monocytes rise and the basophils sometimes along, with a CRP that stays high. And with an underactive thyroid, which slows the whole body, they rise slightly beside a high TSH. In each of those cases they confirm what the other values already say. The one situation in which basophils play the lead is rare. In chronic myeloid leukaemia, a bone marrow disease in which the production of white cells goes astray, a persistently high basophil count is one of the first signs, beside a strongly raised total of white cells and immature cells on the report. Such a picture stands out in the count and a doctor assesses it the same day. It is the reason a count that repeatedly stays far above the band is checked, even without symptoms.

A low count means nothing. Every band starts at zero, cortisol and prednisone suppress the count with stress, illness and an acute allergic reaction, and an ordinary measurement counts only a handful anyway. There is no lower limit that means anything. A high count usually means a mild response, and the other white cells say to what. With high eosinophils and a normal CRP it is an allergy. With high monocytes and a high CRP it is an inflammation that has been running a while. With a high TSH it is an underactive thyroid. A count that repeatedly stays far above the band, certainly with a strongly raised total of white cells and immature cells on the report, is the picture of a bone marrow disease, and that is assessed the same day. Never read basophils alone, but beside the eosinophils, which play the lead in an allergy, beside the monocytes and CRP, which show a longer-running inflammation, and beside the total of white cells and the neutrophils, which say whether the bone marrow as a whole is involved.