Phaeochromocytomas are catecholamine-secreting tumours of the adrenal glands and are rare in cats. Plasma metanephrine levels are widely considered the diagnostic test of choice for phaeochromocytoma in people but have not been investigated in cats. In this study plasma free normetanephrine and metanephrine levels were measured using high-pressure liquid chromatography in healthy cats, sick cats with non-adrenal disease and in a cat with a suspected phaeochromocytoma. Plasma normetanephrine was significantly higher in sick cats with non-adrenal disease compared to healthy cats (P<0.05) and markedly higher in the cat with a suspected phaeochromocytoma when compared to either group. Plasma metanephrine was not significantly different in any of the groups. This study establishes a first-line guide reference range for plasma metanephrine and normetanephrine levels in healthy cats and cats with non-adrenal disease. These results provide rationale for further studies to establish the use of plasma normetanephrine levels as a potential diagnostic test for phaeochromocytoma in the cat.
Background: Up to 2007 there was no formal external quality assurance programme for plasma free metanephrines. A pilot programme was conceived by the AACB (Australian Association of Clinical Biochemists) Working Party on biogenic amines. With support from the AACB and Royal College of Pathologists of Australasia Quality Assurance programmes, a pilot study was developed. Data from this study are presented for the first time. Methods: Twelve lyophilized plasma samples were distributed to 15 centres. Samples were spiked with metanephrine (metadrenaline), normetanephrine (normetadrenaline) and 3-methoxytyramine, all derived from human urine. Concentrations were arranged in a linear relationship. The analytes were present at six levels and samples were duplicated. Results: High-pressure liquid chromatography and tandem mass spectrometry methods showed acceptable precision but in general enzyme immunoassay displayed a higher degree of imprecision as well as a negative bias. Conclusions: Differences in calibration and matrix effects are likely to have been responsible for the discrepancy between chromatographic and immunoassay methods. These differences need to be further examined although efforts at standardization between different methods have been hampered by the lack of a universal calibrator for plasma metanephrines. Meanwhile, a laboratory's performance characteristics can be monitored and enhanced by participation in suitable external quality assurance programmes.
Keywords: pilot study; plasma free metanephrines; plasma total metanephrines; proficiency testing.The diagnosis of pheochromocytoma is based on the quantitation of O-methylated metabolites of catecholamines (1, 2). Several studies have reported high sensitivity of free metanephrines in plasma for assessing the presence of tumour (1). Measurement of plasma total metanephrines (plasma freeqplasma sulphoconjugated metanephrines) has also been proposed as a diagnostically sensitive assay (3). Therefore, an increasing number of laboratories have developed *Corresponding author: Dr. Eric Grouzmann, PhD, Division de Pharmacologie et Toxicologie Cliniques, University Hospital of Lausanne, Lausanne, Switzerland Phone: q41-21-3140741, Fax: q41-21-3144266, E-mail: eric.grouzmann@chuv.ch assays for free and total metanephrines using different analytical procedures including immunoassays (4, 5), high-performance liquid chromatography (HPLC) coupled to amperometric or coulometric detection (6) and liquid chromatography-tandem mass spectrometry (LC-MS) methods (7). Each laboratory is supposed to establish its own reference values and to perform quality control measurements (QCs) with each set of analyses. The internal QC samples usually are prepared by each laboratory and should include plasma samples spiked with known concentrations of both metanephrine (MN) and normetanephrine (NMN). Participation in an external quality assessment scheme (EQAS) allows direct comparisons between all laboratories that measure free and total metanephrines. In this context, the variability of the upper reference limit for free metanephrines reported in the literature is relatively large. For NMN the range varies from 0.6 to 1.4 nmol/L, and for MN it varies from 0.3 to 0.85 nmol/L (1, 2, 8). However, the upper reference limits for total metanephrines are better defined (3, 9, 10). The analytical procedure for the quantitation of metanephrines in plasma is not the only reason for this variability. The characteristics of the control population may also differ between different studies. The absence of a universal calibrator that could be used by all laboratories performing such measurements encouraged us to establish an EQA program for plasma free and total metanephrines. A similar program already exists for metanephrines and catecholamines in urine. The purpose of this letter is to present the results of a pilot study aimed at implementing a proficiency survey for all laboratories measuring plasma free and/or total metanephrines.We selected 10 centres that routinely measure free and/or total plasma metanephrines for diagnosis of pheochromocytoma. Three analytical methods were used. Immunoassays (1 participant), HPLC with electrochemical detection (ECD) (8 participants) including amperometry, coulometry, coularray and LC-MS (1 participant). All but one laboratory, which used an RIA commercial kit method, used in-house methods. Calibrators and internal quality control samples were manufactured using spiked serum pools with standard dilutions of Sigma...
A 31-year-old pregnant patient presented at 13 weeks gestation with a discharging Bartholin's cyst and was found to be hypertensive and diabetic. The biochemical evaluation confirmed pheochromocytoma (PHEO) as a cause of her hypertension. Because PHEO is a potentially surgically curable cause of hypertension and may be fatal if left untreated, a quest for its definitive localization was undertaken. PHEO was not detected on either anatomic (MRI/ CT) or functional (I-123 MIBG SPECT) imaging. Absence of cardiac uptake on I-123 MIBG supported the presence of PHEO. Coincidence PET using F-18 FDG detected the occult tumor. A paraaortic extraadrenal abdominal PHEO was resected, resulting in resolution of her hypertension.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.