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PTD - 220

Test Directory -  Digoxin

Synonyms

Lanoxin

Clinical Indications

Given the relatively narrow therapeutic window of digoxin, with substantial overlap between so-called therapeutic and toxic levels, patients taking digoxin require monitoring of the serum digoxin concentration, with the "optimal" level varying with the clinical setting. Monitoring the serum digoxin level is particularly important in persons with chronic renal dysfunction or rapidly changing renal function, as significantly decreased renal function can lead to accumulation of digoxin and its metabolites and predispose to digoxin toxicity. Additionally, patients with electrolyte disturbances, particularly hypokalemia and hypomagnesemia, which may be related to diuretic therapy or other medications, are at increased risk for digoxin-associated arrhythmias and should undergo monitoring of the serum digoxin level until serum potassium level and magnesium concentration return to the normal range.

Request Form 

Combined Pathology Blood form (Yellow/Black or Blue for GP's). 
Please state time after last dose on request form.

Availability

On request during routine hours. Laboratory must be contacted regarding urgent requests.

Specific Criteria

None

Patient Preparation

Blood samples must be obtained at least 6 hours, but optimally 12 hours, after administration of digoxin to ensure completion of distribution from the blood to the tissues. In patients with advanced kidney disease or who are on hemodialysis, the digoxin level should be checked at least 12 to 24 hours after the prior dose. Serum digoxin concentrations measured prior to these times may be falsely elevated.

Limitations

 

Digibind interferes with digoxin immunoassays therefore digoxin levels are unreliable for 5-7 days after treatment.

Turnaround Time

Same day

Specimen

Serum

Volume

2 ml

Container

Yellow top (SST) tube or

Paediatric orange top (lithium-heparin)

Causes for Rejection

Unlabelled sample

Target Range

0.8 - 2.0 ug/L. Target range in heart failure is 0.5 - 1.0 ug/L

Reference: Pathology Harmony Group, Clinical Biochemistry Outcomes, January 2011 (www. pathologyharmony.co.uk)

A wide range of factors alter clinical response, most importantly hypokalaemia which is associated with enhanced response and may produce digoxin toxicity within the  target ranges. Hypercalcaemia,  hypomagnesaemia and hypothyroidism are also associated with increased tissue sensitivity.

Half-life 

36 - 48 hours

Toxicity

Symptoms include nausea, vomiting, visual disturbances (especially colour vision) bradycardia, sweating, convulsions and coma.

Overdose

An information sheet is available from National Poisons Service (Toxbase).

Lab. Handling

Processing: Test code: DIG. Analysed from primary tube and stored at 4C in the cold room (CB23). (NODIG & save)

 

Version 1.1 / July 2014                                                                                                           Approved by: Consultant Biochemist