The haematology of hypothyroidism

In an unselected series of 202 patients with hypothyroidism anaemia was present on diagnosis in 39 of 172 women and 14 of 30 men. Microcytic anaemia was present in only nine patients in the entire series. The average of the mean corpuscular volume (MCV) of all the patients was 90 fl. Fifty-three of 118 patients who were studied in detail had normal serum concentrations of vitamin B12, folic acid and iron. The haemoglobin was low in 13 of these 53 patients and rose on treatment with thyroxine alone. The MCV exceeded 90 fl in 29 of these 53 patients and in three it was greater than 100 fl. The MCV invariably fell on treatment with thyroxine even if the initial value was within the normal range. Nine of this group of 53 patients had both anaemia and an increased MCV--the macrocytic anaemia of hypothyroidism. A minor degree of anisocytosis of the red blood cells, which was reduced by treatment with thyroxine, was also demonstrated. Acanthocytes were present in the blood films of 32 out of 172 patients but in only five did the abnormal cells comprise more than 0-5 per cent of the red cell population. The incidence of new cases of pernicious anaemia diagnosed concurrently with the hypothyroidism in the carefully studied group of 118 patients was 8-5 per cent. The MCV of hypothyroid patients with low levels of vitamin B12 was often no greater than in patients with uncomplicated hypothyroidism. The MCV is not therefore a useful discriminant in the diagnosis of pernicious anaemia in hypothyroidism. The serum iron concentration was less than 12 mumol/1 in 60 out of 118 patients. The total iron binding capacity of the serum was increased in only 21 of these 60 patients. In 42 hypothyroid patients the low serum iron concentration was not associated with low levels of either vitamin B12 or folate and of these patients 22 were anaemic. Despite the very low percentage saturation of the iron binding capacity in all of these patients with a low serum iron, a lack of iron did not seem to be the usual determinant of anaemia when it occurred.