Comparability of a new turbidimetric digoxin test with other immunochemical tests and with HPLC--a multicenter evaluation.
A new turbidimetric inhibition immunoassay for digoxin (Tina-quant [a] Digoxin, Boehringer Mannheim) was evaluated in seven laboratories. It can be performed without sample pretreatment with ready-to-use reagents on nondedicated analyzers in combination with routine clinical chemistry. The studies revealed a good analytical performance: lower limit of detection 0.12 microg/L (3 SD from mean of blank); linearity up to 7.5 microg/L; median between-run CVs 8.1% (0.6 microg/L), 2.8% (1.5 microg/L), 1.9% (3 microg/L); mean analytical recovery in control sera 98-102%; slopes from 0.97 to 1.09 and intercepts from -0.28 to 0.10 microg/L in comparison with four immunoassays; and a high resistance to common interferents. The test was more resistant to digoxin-like immunoreactive factor (DLIF) interference than other methods, showing cross-reactivity only in some intensive care patient samples. Among 192 patients in whom DLIF is expected (e.g., pregnant women, patients with renal failure, newborns), 90% of results were < or =0.26 microg/L digoxin. Cortisol showed no cross-reactivity and digoxigenin had a low reactivity. An interlaboratory survey revealed a good comparability of the Tina-quant [a] test with the median of all methods (slope 0.99, intercept -0.06 microg/L). An HPLC method for digoxin based on isocratic separation of samples on an RP-18 column followed by detection by an immunoassay yielded a reasonable comparability with the immunochemical tests with noncritical samples. Divergent results of immunoassays caused by DLIFs or different cross-reactivities with digoxin metabolites or derivatives can be explained by the use of this HPLC method.
Scholer
A
A
Klinisch-Chemisches Laboratorium, Kantonsspital Basel, Switzerland. scholer@ubaclu.unibas.ch
Boecker
J
J
Engelmayer
U
U
Feldmann
K
K
Hannak
D
D
Kattermann
R
R
Oellerich
M
M
Raith
H
H
Schlebusch
H
H
Wieland
H
H
Willems
D
D
Jarausch
J
J
Domke
I
I
D000925:Anticoagulants; D002851:Chromatography, High Pressure Liquid; D003422:Critical Care; D004077:Digoxin / Q000097:blood*; D005260:Female; D006801:Humans; D007118:Immunoassay / Q000379:methods* / Q000706:statistics & numerical data; D007202:Indicators and Reagents; D007231:Infant, Newborn; D007753:Laboratories; D009391:Nephelometry and Turbidimetry / Q000379:methods*; D011247:Pregnancy; D011786:Quality Control; D012016:Reference Values; D006435:Renal Dialysis; D051437:Renal Insufficiency / Q000097:blood; D012680:Sensitivity and Specificity
D000925:Anticoagulants; D007202:Indicators and Reagents; D004077:Digoxin