Freedom from drug interference in new immunoassays for urinary catecholamines and metanephrines.
BACKGROUND
Determination of urinary free catecholamine and total (i. e., free plus conjugated) metanephrine excretion is considered the most clinically sensitive biochemical test for pheochromocytoma. In this study, we evaluated new immunoassay methods for the measurement of these analytes for potential drug-based interference.


METHODS
Urine samples collected from patients on a variety of medications were grouped by specific drug type. The significance of any difference in the free catecholamine or total metanephrine concentrations in the different groups was assessed by one-way ANOVA. A group of patients receiving no medication was included as a control (no analytical interference). Additionally, analytical accuracy, detection limit, and precision were determined.


RESULTS
No significant differences were found in the concentrations of free catecholamines or total metanephrines in urine from patients taking the medications investigated and the control group: P = 0.649 (fE), 0.221 (fNE), 0.149 (tM), and 0.170 (tNM). For free catecholamines, intraassay CVs were 4.6-18%; interassay CVs were 10-25%. For total metanephrines, intraassay CVs were 9.6-27%; interassay CVs were 5. 8-22%. Detection limits were 0.009 and 0.027 micromol/L for fE and fNE and 0.119 and 0.346 micromol/L for tM and tNM, respectively.


CONCLUSIONS
None of the drugs examined in this study interfered in the measurement of free catecholamines or total metanephrines by these immunoassays. The technique is easier to use, requires less equipment, and is more accessible than HPLC. In combination, these assays are suitable as initial screening tests for pheochromocytoma.
Wassell
J
J
Department of Biochemistry, Wythenshawe Hospital, Southmoor Rd., Manchester M23 9LT, UK. juliewassell@hotmail.com
Reed
P
P
Kane
J
J
Weinkove
C
C
D000319:Adrenergic beta-Antagonists / Q000627:therapeutic use; D000704:Analysis of Variance; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000627:therapeutic use; D002121:Calcium Channel Blockers / Q000627:therapeutic use; D002395:Catecholamines / Q000652:urine*; D002851:Chromatography, High Pressure Liquid; D004232:Diuretics / Q000627:therapeutic use; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D008676:Metanephrine / Q000652:urine*; D010673:Pheochromocytoma / Q000188:drug therapy / Q000652:urine; D011786:Quality Control; D011863:Radioimmunoassay / Q000379:methods*; D012680:Sensitivity and Specificity
D000319:Adrenergic beta-Antagonists; D000806:Angiotensin-Converting Enzyme Inhibitors; D002121:Calcium Channel Blockers; D002395:Catecholamines; D004232:Diuretics; D008676:Metanephrine