Background: Patients with hypertension often have increased 24-h
excretion of urinary free catecholamines (UFCA) compared with normotensive patients,
but the extent to which β-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 β-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 β-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 β-blockers.
