Abstract
Studies conflict concerning the use of enzyme immunoassays (EIA) for plasma free metanephrines (P-MNs) vs. other methods for pheochromocytoma/paraganglioma (PPGL) diagnosis. We compared commercially available EIAs for P-MNs with high-pressure liquid chromatography (HPLC) for 24 h-urinary MNs (U-MNs) and -catecholamines (U-CATs). 943 (565 female, 378 male) patients (54 PPGL, 889 Non-PPGL) were studied. Simultaneous measurements of all parameters analyzed at the central lab of our university hospital was mandatory for inclusion. Sensitivity of P-MNs (94.4%) was similar to that of U-MNs (100%), and both were higher than of U-CATs (77.8%), specificity of P-MNs (100%) higher than of U-MNs (73.6%), and similar to U-CATs (99.8%). With the recently proposed downward adjusted ULN of P-MNs to correct for the reported negative bias of the EIAs sensitivity (98.1%) raised non-significantly, but specificity decreased significantly (94.8%). Areas under receiver-operating characteristic curves indicated comparable diagnostic performance of P-MNs (0.989) vs. U-MNs (0.995), both better than U-CATs (0.956). In summary, the EIAs to measure P-MNs performed similarly to U-MNs by HPLC, and both better than U-CATs by HPLC. The post-test probability of PPGL given a positive test result was best for P-MNs, and higher than for the other pairs of analytes. Downward corrections of ULN of P-MNs did not improve test performances.
Highlights
Pheochromocytomas (PHEO) and paragangliomas (PGL; together: PPGL) are rare catecholamineproducing tumors estimated to occur in about 2–8 out of 1 million people per year [1]
Based on the non-availability of these methods, we report our experience of n = 943 patients tested for PPGL in routine clinical care, in every patient and simultaneously using the three test methods routinely available, compute which performs best for which metabolites to be analyzed, and compare the methods between each other
Our study provides evidence of equal diagnostic performance as quantified by the area under the curve (AUC) of receiver–operating curve (ROC) curves of a commercially available enzyme immunoassays (EIA) kit for the measurement of plasma free metanephrines (P-MNs), when compared to a high-pressure liquid chromatography (HPLC) for urinary metanephrines (U-MNs), and that both methods perform better than the determination of 24 h-urinary catecholamines (U-CATs) by HPLC
Summary
Pheochromocytomas (PHEO) and paragangliomas (PGL; together: PPGL) are rare catecholamineproducing tumors estimated to occur in about 2–8 out of 1 million people per year [1]. The prevalence in the hypertensive population is 0.1–0.5% [1,2,3], in an unselected hospital referral population 0.8–1.6% [4,5,6], and in patients with adrenal incidentalomas about 5% [7]. Those with a history of PPGL have a risk of recurrence as high as 16.5% [8], and 30–40% of PPGL may be associated with a hereditary disease [1,9], all scenarios typical of a large referral hospital and a specialized endocrine unit, respectively. Even in university hospitals, commercially available enzyme-linked immunoassays (EIAs) for the determination of plasma metanephrine (MN) and normetanephrine (NMN) are in widespread use due to their low price, ease of handling and—compared to chromatographic/MS methods—greater likelihood of being certified by ISO (International Organization for Standardization, Geneva, Switzerland) norms
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