Background: Patients with hypertension often have increased 24-h excretion of urinary free catecholamines (UFCA) compared with normotensive patients, but the extent to which beta-blockade and other antihypertensive agents affect 24-h UFCA concentrations remains unclear. Consequently, many patients with slightly elevated 24-h UFCA concentrations are not adequately investigated for the presence of phaeochromocytoma.
Method: We undertook a retrospective study on patients with at least one abnormal 24-h urinary collection of adrenaline (Adr), noradrenaline (NA) or dopamine (DA) between July 1997 and December 1999 to assess these issues.
Results: Of the 168 patients identified with raised 24-h UFCA concentrations, 106 with hospital notes were audited. Of the 46 patients whose values were more than twice the upper reference limit, 24 had their result confirmed with a repeat sample and only 10 underwent computed tomography or m-iodobenzylguanidine scanning. Two patients of these 10 had a phaeochromocytoma. We observed that hypertension correlated with significantly increased NA excretion compared with normotensive patients (median value 490+/-222 nmol per 24 h versus 304+/-229 nmol per 24 h, P<0.005). Patients on beta-blockers showed a trend towards significantly increased NA excretion (P=0.08).
Conclusions: Many patients with abnormal 24-h UFCA excretion are not thoroughly investigated for the presence of phaeochromocytoma. NA concentration is significantly raised above the reference limit for patients with hypertension, and the use of beta-blockers showed a trend towards a further elevation in NA concentrations. Care must therefore be taken when interpreting abnormal NA concentrations in patients with hypertension or in those taking beta-blockers.