A NEW DIGOXIN IMMUNOASSAY SUBSTANTIALLY FREE OF INTERFERENCE BY DIGOXIN IMMUNOREACTIVE FACTOR

We have evaluated the new Roche digoxin ''On Line'' procedure for use in a pediatric population with particular interest in the potential fo r interference by digoxin-like immunoreactive factor (DLIF). An initia l study comparing digoxin values obtained with the new Roche procedure with determinations on an Abbott TDx, American Dade Stratus, and COBA S-FARA using Microgenics Cedia reagents, found good correlations with these established methods. The Roche method was suitably precise and u tilized either serum or plasma. Interference by DLIF was assessed by a nalyzing specimens from patients not receiving digoxin but likely to c ontain DLIF, with the argument that non-zero values represent cross-re activity of anti-digoxin antibodies with DLIF endogenous to these spec imens. When specimens from neonates, women with second/third trimester pregnancies, and patients with renal and liver failure were assayed w ith the Roche, Stratus, and TDx methods, all three methods measured DL IF in some specimens, but the Roche method possessed the lowest overal l DLIF interference. The modest extent of DLIF interference and the re quirement of a small amount of specimen make the Roche method superior in monitoring digoxin in a pediatric population.