Non-pretreatment digoxin assays and developments in immunoanalyzers

The performance of a new, non-pretreatment digoxin assay for the Abbott IMx analyzer (Abbott Park IL) was evaluated to determine its reliability and suitability for routine clinical use. The operational characteristics of 1st, 2nd and 3rd generation immunoanalyzers are compared and contrasted.

Within-run and day-to-day precision of the assay was determined, as well as its limit of detection. The effect of digoxin-like immunoreactive factors and carryover were evaluated. Serum from patients receiving digoxin was analyzed using the Dade Stratus II (Miami FL) digoxin test as the reference method and the IMx digoxin test as the comparison method.

An independent reference laboratory specializing in serving long-term care facilities.

Specimens were analyzed from geriatric patients in long-term care facilities who receive digoxin as a therapeutic drug for cardiac arrhythmias. Specimens were also tested from individuals in this same population, not receiving digoxin but demonstrating the presence of digoxin-like immunoreactive factors.

Comparability of results from a new nonpretreatment digoxin with the standard digoxin assay (Stratus II) was used to determine the suitability of the new test for routine clinical use.

The limit of detection is 0.27 ng/mL; day-to-day precision ranges from 3.4% CV to 5.9% CV. Linear regression analysis generated the following equation: IMx = 0.968 Stratus + 0.1043, r = 0.9776, n = 237. No significant interference from digitoxin-like immunoreactive factors was noted.

The IMx nonpretreatment digoxin assay's performance matches the manufacturer's claims, compares favorably with another common automated digoxin test, and is suitable for routine clinical use.