Freedom from Drug Interference in New Immunoassays for Urinary Catecholamines and Metanephrines

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 med...

Drug interference with measurement of metanephrines in urine.

The influence of 35 commonly used drugs on measurement of metanephrines in urine was evaluated. Two concentrations of drugs were chosen for study based on usual doses and the percent of dose excreted unchanged in the urine. At "medium" drug concentrations, only phenylephrine falsely elevated metanephrine levels, whereas at a 10-fold higher drug concentration, guanethidine, hydrocortisone, imipr...

Stability of urinary fractionated metanephrines and catecholamines during collection, shipment, and storage of samples.

BACKGROUND Measurements of 24-h fractionated urinary metanephrines and catecholamines are used for the diagnosis of pheochromocytoma, but adequate information is needed regarding collection, storage, and shipment conditions. METHODS Spot urine samples were collected from 8 healthy volunteers. Aliquots were immediately frozen at -20 degrees C, or acidified to pH 4 and then frozen either direct...

Screening for interference in immunoassays.

Screening for interference in immunoassays.

BACKGROUND The presence of interfering substances in patient samples submitted for immunoassay cannot be reliably anticipated. We therefore evaluated three interference screening techniques and estimated the prevalence of interfering substances as defined by positive outcomes with these protocols. METHODS We evaluated 160 samples for the presence of substances that may interfere with four imm...