Investigation of the possible influence of using blood pressure lowering drugs on plasma free metanephrines concentrations.

Since the characteristic of pheochromocytoma is the increased catecholamine
(eprinephrine, norepinephrine and dopamine)production in the tumor, its
diagnosis is mainly based on clinical chemical results. In order to
demonstrate the increased catecholmaine production, free catechooamines and/or
their metabolites are measured in urine and/or plasma. The analysis of the free
form of 3-O-metabolized catecholamines (metanephrine, normetanephrine and
3-methoxytyramine) in plasma is the most sensitive and specific method.
Therefore the measurement of plasma free metanephrines is the golden standard
for the diagnosis of pheochromocytoma. This method is, as far as known, not
susceptible to analytical interferences. In contrast, physiological
interference could be possible for example by the use of blood pressure
lowering drugs, since such medication acts on teh catecholamine biochemistry.
However, it is currently unknown whether the use of these drugs causes
false-positive results when measuring plasma free metanephrines.

The objective of the study is to determine whether it is necessary to take the
blood pressure lowering medication (β-blocker, ACE-inhibitors or diuretics) of
a patient into account prior to blood sampling for pheochromocytoma
diagnostics. Therefore the influence of the use of this medication on plasma
free metanephrine concentrations is established. Every patient is its own
control.

Primary reserach question:
Does the use of beta-adrenoreceptor blocking drugs, angiotensine converting
enzyme inhibitors or diuretics cause an increase of plasma free metanephrines
which leads to false-positive pheochromocytoma diagnosis and is it therefore
necessary to stop this medication prior to blood sampling?

Secundary reserach question:
Is there a difference between the use of a β-blocker, ACE-inhibitor or
diuretics as blood pressure lowering drug?

Fifty adults are asked to join the study when through screening by the general
practitioner or physician untreated hypertension, peripheral oedema,
palpitations or migrain was discovered. Subsequently 10 ml extra blood is drawn
during routine measurements for the determination of the metanephrines basal
concentrations, and the β-blocker, ACE-inhibitor or diuretics are prescribed.
After one-three months of treatment the patient is seen for follow-up. Blood
pressure is measured again and again 10 ml extra blood is drawn for the
analysis of plasma free metanephrines.
Blood is sampled in sitting position by venapunction, in addition to the
routine blood sampling.
Metanephrines are quantitated by isotope dilution mass spectrometry.

Blood pression lowering drugs in the normal treatment of hypertension.

During a regular visit to the general practitioner or physician, blood will be
sampled twice: before treatment with a blood pressure lowering drug and after
one-three months of treatment. Medical risks due to participation in the study
is minimal.