Endocrine Abstracts

Quantification of the catecholamine metabolites, normetadrenaline, metadrenaline and the dopamine metabolite 3-methoxytyramine is widely used as a biochemical investigation for the presence of a phaeochromocytoma. As with any biochemical measurement it is essential that the results are compared against a reference range appropriate for the individual patient.

In order to assess the suitability of published reference ranges for these analytes, observed results for patients under investigation for possible phaeochromocytoma were examined for effect of gender or age.

In 423 patients (185 male, 238 female) of median age 47.5 yrs (range 1 to 88), in whom a phaeochromocytoma had been excluded, there appeared to be a clear trend upwards with age for urinary normetadrenaline in both males and females (p<0.0001). The median value in patients aged 20-40 years was 1.25 micromol/24hrs (95thcentile 3.30) compared to 1.72 micromol/24hrs (3.06) in those aged 40-60 yrs and 1.86 micromol/24hrs (3.74) in those over 60 yrs. Metadrenaline and 3-methoxytyramine did not show a change with age and none of the three fractions showed a difference between the genders.

A subgroup of 120 patients (45 male, 75 female) aged 21-85 years was selected after excluding conditions which may affect catecholamine metabolite output e.g. stress of hospital admission or chronic cardiac, renal or endocrine diseases. The upward trend with age for urinary normetadrenaline was still present. Results in patients attending cardiac clinics were not different from those in other patients of a similar age and the trend was still present in patients admitted acutely despite some of the highest normetadrenaline results.

When interpreting urinary metadrenalines results, reference ranges for the normetadrenaline fraction should be age-related but this is not necessary for the other fractions. Factors known to increase catecholamine output do not appear to be the main cause of the increased normetadrenaline levels seen in the older age groups.