DIGOXIN, WRHA & Westman Lab (ROCHE) - (P)

Test Code: DIG

Alternate Name(s): Toloxin, Lanoxin

Description: Digoxin is a cardiac glycoside, widely used for the treatment of congestive heart failure and disturbances of cardiac rhythm.

Test Indications: Routine Digoxin monitoring is not recommended and should not be used to guide chronic therapy. Digoxin levels are most useful when assessing for toxicity.
 
Patients with reduced renal function, elder patients, and those with low body mass are at increased risk of Digoxin toxicity and may require closer monitoring.

Patient preparation instructions: Samples should be collected at trough levels, just prior to the next dose of Digoxin, or at least 12 hours since the last dose (oral or IV). Steady state concentrations of Digoxin take approximately 1 week to achieve after initiation of therapy.
 
If toxicity is suspected, samples may be collected at any time.
 
If the patient is also being treated with spironolactone, collect sample BEFORE the next dose, as spironolactone concentrations of 15 mg/L or greater may falsely elevate Digoxin results.
 
Multivitamins (45–125 µg biotin) or biotin-only supplements up to 1 mg per day do not interfere with this test. Samples should not be taken from patients receiving therapy with high biotin doses (i.e. >5 mg/day) until at least 8 hours after the last dose.

Do not use separator gel.

_SH Biochemistry Hematology Requisition (R250-10-92)

_SH Hospital Biochemistry Hematology Non Winnipeg Brandon (R250-10-91)

_SH Winnipeg Brandon Biochemistry Hematology Requisition (R250-10-94)

_SH Winnipeg Brandon Hospital Biochemistry Hematology Requisition (R250-10-93)

Reference Intervals: 
Therapeutic: 0.8 – 2.0 μg/L
Toxic: > 2.4 μg/L
 
Diagnosis of Digoxin toxicity should be based on the combination of clinical and biochemical findings.

Critical Value: > 2.5 μg/L

Method of Analysis: Roche competitive Electrochemiluminescent Immunoassay (ECLIA)
 

Stat or Routine

Interpretation & Assay Interferences: Spironolactone may cause falsely elevated Digoxin values when exceeding 15 mg/L
Hydrocortisone may cause falsely elevated Digoxin values when exceeding 10 mg/L
 
Substances that cause falsely elevated Digoxin values at their recommended daily dose include:

• Uzara (milkwort)
  Nabumetone (Relafen)
  Pentoxifylline
  Canrenone

Digoxin Like Immunoreactive Substances (DLIS) present in patient samples can result in falsely elevated or lowered Digoxin values when tested by immunoassay. Patient populations which are at higher risk of developing DLIS include those with renal failure, liver failure, in the 3rd trimester of pregnancy, or those who have been taking Digoxin for several years.
 
Rarely, interference due to extremely high antibody titres against assay components can cause spurious results.
References:
1. Roche Diagnostics GmbH. (2022). Elecsys Digoxin. [Package Insert; v 5.0 Eng].  Mannheim, Germany.
2. Dasgupta A. 2002. Endogenous and exogenous digoxin-like immunoreactive substances: impact on therapeutic drug monitoring of digoxin. Am J Clin Pathol. 118: 132-140
3. Ezekowitz JA, O’Meara E, McDonald MA et al. 2017. Can J Cardiol. 33(11) : 1342-1433.