Endocrine Abstracts

Background: Phaeochromocytomas (PC) are rare tumours of chromaffin cells which may present with relatively common and non-specific symptomatology. The optimal biochemical investigation to confirm or refute the diagnosis remains unclear; some centres use fractionated plasma metanephrines, which are very sensitive but lack specificity, while others use conventional measurements of urinary metanephrines, which may be affected by concurrent drug administration and are less sensitive. We examined the test characteristics of a new, specific assay of urinary fractionated metanephrines in patients with and without phaeochromocytomas.

Methods: We undertook a retrospective case record study of patients investigated or treated at the Mayo Clinic, Rochester, MN. Permission was obtained from the local Institutional Review Board. Using tandem mass spectrometry, fractionated urinary metanephrines were measured in 482 patients investigated for PC who were subsequently shown not to have this diagnosis, and in 103 patients with proven secretory PC.

Results: Metanephrine, normetanephrine and total metanephrine measurements were analysed. Receiver operating characteristic (ROC) curves demonstrated that total metanephrines had the most favourable characteristics (AUC 0.991, 95% CI 0.986, 0.997), followed by normetanephrine (AUC 0.973, 95% CI 0.955, 0.990), and then metanephrine (AUC 0.798, 95% CI 0.740, 0.856). Individual sensitivities and specificities at set cut off values (in micrograms/24 hours) were as follows: total metanephrines of 974.0 -sensitivity 95.1%, specificity 95.4%; normetanephrine of 610.5 - sensitivity 95.1%, specificity 91.5%; metanephrine of 99.5 - sensitivity 93.2%, specificity 29.3%.

Conclusion: The sensitivity and specificity of fractionated urinary metanephrines for the diagnosis of PC are excellent. The tandem mass spectrometry assay for fractionated metanephrines is a very good option for the clinician when testing for PC.