Specimen Collection

Specimens must be taken at least six hours after the last oral dose.

Sample stability:

• 24 hours at 2-8 ^o C
• 1-2 weeks at -20 ^o C

External Referrers: Please separate plasma/serum, freeze at -20 ^o C and transport frozen on ice.

4.5 mL PST Blood (Preferred)

0.5 mL Paediatric Micro-PST Blood (Preferred)

5 mL Heparin Blood

4 mL Plain Blood

3.5 mL SST Blood

0.5 mL Paediatric Microsample Serum

0.6 mL Paediatric Micro-heparin Blood

0.5 mL Paediatric Micro-SST Serum
Reference Intervals

Units: nmol/L

Therapeutic interval: Atrial fibrillation: 0.6 - 2.0 Heart Failure: 0.6 - 1.0

Uncertainty of Measurement: 0.2 nmol/L at a concentration of 0.7 nmol/L

10% at a level of 2.0 nmol/L and higher

Conversion factor : ng/mL x 1.28 = nmol/L

Turnaround Time: Within 3 hours

Urgent sample within 1 hour. Contact laboratory to notify.

Assay Method

Principle: Turbidometric/ Tinaquant

Assay: Roche TDM Digoxin

Analyser: Cobas c502

Diagnostic Use and Interpretation

MONITORING

Maximum serum levels are reached 1 - 2 hours after an oral dose. The level then falls rapidly for 3 - 5 hours as it is distributed. The serum levels then fall with a half life of 1.5 - 2 days. Monitoring should therefore be performed on specimens collected at least six hours after the last oral dose.

The irregular rhythm from a toxic level sometimes mimics atrial fibrillation. Measuring the serum level will help decide whether insufficient or excessive digoxin dosage is the underlying problem.

For digoxin use in congestive heart failure, aim to keep the plasma digoxin level at 0.6-1.0nmol/L.

For digoxin use in rate control of atrial fibrillation, the therapeutic interval for digoxin is 0.6-2.0nmol/L.

Toxic level: usually >2.6nmol/L but can occur at level <2.6nmol/L. Patients with renal dysfunction are especially prone to digoxin toxicity because of the prolonged half-life of the drug. Toxicity is more likely in situation of hypokalaemia and hypercalcaemia even when the digoxin level is within the therapeutic interval

Spironolactone at doses = 100 mg/d may cause negative interference in some digoxin assays. The LabPlus digoxin assay is NOT affected by spironolactone.

Ref: Steiner et al. Clin Chem. 48(3),507-16,2002.

Contact Information

Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.

If the query concerns a specific patient please include the NHI number in your email.

If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).

Individual chemical pathologists may be contacted but will not be available at all times.

After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.

Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402

Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052

Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427

Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427

Dr Sakunthala Jayasinghe: Sakunthala@adhb.govt.nz ext. 23427

Dr. Hima Madhavaram, Toxicologist: ext 22057

Last updated at 15:26:00 06/01/2025