Phaeochromocytomas (PC) are tumours of the adrenal medulla and paragangliomas (PGL) refer to their extra-adrenal counterpart arising from sympathetic or parasympathetic tissue. Mutations in the citric acid cycle enzyme succinate dehydrogenase (SDH) predispose to PC/PGL. Clinical practice guidelines suggest that plasma metanephrine and normetanephrine levels measured in the supine position should be used in the first instance for biochemical diagnosis, and those with positive results should have CT imaging for tumour localisation. The aim of this review was to determine if plasma metanephrine testing was a sensitive biochemical-screening test in patients with SDH mutations. A retrospective review of 32 patients (14 with SDH mutations) diagnosed with a PC/PGL in Cambridge University Hospital over a 10 year period was performed. A review of the plasma metanephrine levels at first diagnosis for each patient was carried out. In the SDH group mutations included: 66.6% in SDHB, 20% in SDHC, 6.7% in SDHD, and 6.7% in SDHA. The average age at diagnosis was 45.3 years, compared to 44.3 years in the no-mutation cohort. Phenotypes varied between groups; in the SDH cohort, 50% of tumours were head and neck paragangliomas and remaining 50% were abdominal paragangliomas. In the no-mutation cohort, 72% of tumours were adrenal phaeochromocytomas. In the SDH mutation cohort, the mean plasma metanephrine level was 199.5 pmol/l (±33.3 S.D.), compared to 1399.6 pmol/l (±2242.1 S.D.) in the no-mutation cohort (P-value 0.0364). The mean normetanephrine level was 1444.5 (±1964.4 S.D.), compared to 12 087.4 (±21 275 S.D.) in the no-mutation cohort (P-value 0.049). This study highlights that plasma metanephrine testing is a less sensitive biochemical-screening test in patients with SDH mutations due to the associated phenotype. Plasma methoxytyramine as an adjunct to plasma metanephrines may improve the sensitivity of biochemical screening in this cohort.