Interference in Pisano’s Urinary Metanephrine Assay after Use of X-Ray Contrast Media

Abstract

Certain radiopaque dyes ("Renovist" and "Renografin") contain methylglucamine salts of diatrizoate, which interfere in the Pisano cationexchange method for measuring urinary metanephrine. Methylglucamine is adsorbed to the resin and eluted with the metanephrines. It then consumes the periodate, preventing oxidation of the metanephrines to vanillin and leading to falsely negative results. The methylglucamine can be separated from the metanephrines by adsorbing the metanephrines on QAE Sephadex A-25 acetate at pH 11.2.

Urinary sampling for 5HIAA and metanephrines determination: revisiting the recommendations

“…Early colorimetric or fluorimetric assays exhibited many drug-elicited interferences ( 100 , 101 , 102 , 103 , 104 , 105 ). These drugs should not cause interference with electrochemical or mass spectrometric assays.…”

Measurement of catecholamines and their metabolites

“…The original spectrophotometric procedure reported by Pisano 15 may still be in use, and laboratories using this procedure for initial screening of urine samples should be aware of the many limitations associated with this procedure. 95,96 Chromatographic methods HPLC-based techniques for the measurement of metadrenalines o¡er a more practical approach than GC or £uorimetric procedures, as uniform HPLC conditions can be utilized for both urinary catecholamines and metadrenalines. 68,70 Extraction of the metadrenalines from acid-hydrolysed urine has generally been achieved using weak cation-exchange resins of the sulphonic or carboxylic functional types as advocated by Pisano.…”