Pentolinium Suppression Test

INDICATION

To try and exclude the diagnosis of phaeochromocytoma in patients with hypertension and borderline changes in plasma catecholamines or 24 hour urinary catecholamines.

CONTRAINDICATIONS

No absolute contraindications but beware frail patient and patients with severe coronary or carotid vascular disease.

SIDE EFFECTS

May cause severe transient hypotension

PREPARATION

Order the Pentolinium from pharmacy (difficult to obtain). It comes as 10 mg/ml.
Stop hypotensive treatment for at least 24 hours before the test (especially centrally acting drugs such as methyldopa).
Fast overnight.
Quiet environment.
Sphygmomanometer or Critikon BP monitor.
Cannula, 19g.
Ice.
Lithium heparin tubes (green top Vacutainer).
Contact biochemistry laboratory who measure catecholamines before doing the test, enquire how they would like the samples taken and arrange for their delivery.

METHOD

1. Rest for 1/2 hour.
2. Monitor BP and pulse at onset and every time blood taken.
3. Take 2 baseline samples at 5 minute intervals for catecholamines. Blood needs to be taken into Lithium heparin, kept on ice, spun at 4°C, frozen until assay.
4. At time 0, give 2.5 mg Pentolinium i.v.
5. Take blood at one hour.

INTERPRETATION

Pentolinium is a sympathetic ganglion blocker. Normal subjects may show an initially elevated plasma adrenaline and noradrenaline but these will fall to within the normal plasma range with Pentolinium. In contrast the autonomous secretion of a phaeochromocytoma will not suppress.

SENSITIVITY AND SPECIFICITY

This test has a low false positive and false negative rate as determined in series of known phaeochromocytomas and normals but published information is very scanty. The most likely theoretical problem is a fall in plasma catecholamine levels in a phaeochromocytoma patient whose tumour is only secreting episodically.

REFERENCES

Brown MJ et al. Lancet 1981; 1: 174-7