Blood and urine histamine levels in normal and pathological states as measured by a radiochemical assay.

The utility of the enzymatic radiochemical assay of histamine in diagnosing diseases with known abnormalities in histamine production was investigated. Whole blood histamine levels were abnormal only in patients with basophilia, i.e. chronic myelocytic leukemia or polycythemia vera. Histamine was not detectable (less than 1 ng/ml) in normal plasma but was detected in plasma of some patients witheither mastocytosis or chronic myelocytic leukemia. These patients also had symptoms which could be attributed to histamine release as, for example, hyperchlorhydria and hypotension. Urinary histamine excretion was also abnormally high in these diseases compared to normal subjects (range less than 5-42 microgram/24 h, n = 31). Patients with systemic mastocytosis had higher urine values (greater than 150 microgram/24 h) than those with cutaneous mastocytosis (39-88 microgram/24 h), and the urinary histamine excretion appeared to be an index of the severity of the diseases. Studies with L-histidine loading suggest that the kidney is one possible source of urinary histamine.