Measurement of urinary histamine: comparison of fluorometric and radioisotopic-enzymatic assay procedures.

Assessment of urinary histamine may prove useful in determining the role of histamine in human health and disease. Urinary histamine may be accurately estimated by a modified fluorometric assay employing diamine oxidase (DAO) digestion and cation-exchange chromatography. Normal urine histamine values obtained by this assay are: arithmetic means (+/- SEM), 8.6 +/- 0.6 ng/ml and 10.5 +/- 0.7 micrograms/24 hr; geometric means (+/- SEM), 6.2 +/- 1.1 ng/ml and 10.0 +/- 1.3 micrograms/24 hr. However, the radioisotopic-enzymatic assay is less expensive, easier to perform, and possibly more sensitive. Therefore the two procedures were compared. The radioenzyme assay was found to be affected by factors in urine (possibly salt concentrations) requiring extraction of histamine from urine by butanol-heptane. Moreover, it was found to be necessary to compare DAO-digested samples with undigested samples to accurately estimate histamine levels and to run the standard curve of histamine in DAO-digested urine. Even with these modifications, the radioenzyme assay was not as accurate as the fluorometric assay for urine samples having histamine values about 60 ng/ml. Therefore we recommend utilization of the modified fluorometric assay for the measurement of urinary histamine levels.