Digoxin, Free, plasma or serum

Alternate test name

Lab area

Clinical Biochemistry - TDM & Toxicology

Method and equipment

Equipment : Roche Cobas Pro c503

Method : Kinetic interaction of microparticles in solution (KIMS) as measured by changes in light transmission.
The Digoxin assay is a homogeneous immunoassay based on the principle of measuring changes in scattered light or absorbance which result when activated microparticles aggregate. The microparticles are coated with digoxin and rapidly aggregate in the presence of a digoxin antibody solution. When a sample containing digoxin is introduced, the aggregation reaction is partially inhibited, slowing the rate of the aggregation process. Antibody bound to sample drug is no longer available to promote microparticle aggregation, and subsequent particle lattice formation is inhibited. Thus, a classic inhibition curve with respect to digoxin
concentration is obtained, with the maximum rate of aggregation at the lowest digoxin concentration. By monitoring the change in scattered light or absorbance, a concentration‑dependent curve is obtained.

Expected turn-around time

STAT/Urgent: 3 hours Routine: 24 hours

Specimen type

Serum, Plasma (Heparin)

Specimen requirements

500 uL

Storage and transportation

4°C (transport with a cool pack if possible)

Background and clinical significance

Refer to the Digoxin (Total) for a complete description of the clinical significance of Digoxin.

In patients receiving either Fab antibodies, such as Digibind, for treatment of digoxin toxicity or in patients with digoxin-like immunoreactive factors (DLIFs), such as neonates, patients with renal or liver disease, and women in the third trimester of pregnancy being treated with digoxin.

Digoxin-like factors are strongly bound by protein, and measurement of digoxin in the ultrafiltrate provides the free digoxin concentration and separates it from the cross-reactive DLIFs. In this way, the physician can evaluate the patient's digoxin status even in the presence of Digibind or DLIFs. By multiplying the conventional therapeutic range of 1.0 to 2.5 nmol/L by 0.8, one arrives at a therapeutic range for free digoxin of 0.8 to 2.0 nmol/L.

Finally, patients receiving Digibind will have very high plasma or serum concentrations of digoxin when measured by most methods. This is because the Fab antibody Digibind draws digoxin out of skeletal muscle and heart tissue. This Fab-bound digoxin is not pharmacologically active digoxin, and for this reason measurement of free digoxin in the ultrafiltrate is strongly recommended.

Disease condition

Cardiac Glycoside