Digoxin

Heart

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Drug monitoring for digoxin.

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Digoxin Test Information Guide

Why is it done?
- Test Purpose: Measures the concentration of digoxin in the blood to monitor therapeutic levels and detect toxicity
- Primary Indications: Monitoring patients on digoxin therapy for heart failure or atrial fibrillation; evaluating suspected digoxin toxicity; assessing medication efficacy and determining appropriate dosing
- Clinical Circumstances: Initial baseline testing after starting digoxin; periodic monitoring at steady state; when symptoms of toxicity appear (nausea, arrhythmias, visual disturbances); after dose adjustments; when renal function changes; if drug interactions suspected; during acute illness
Normal Range
- Reference Ranges: Therapeutic range: 0.5-2.0 ng/mL (0.64-2.56 nmol/L)
- Units of Measurement: ng/mL (nanograms per milliliter) or nmol/L (nanomoles per liter)
- Interpretation Guide: • Below 0.5 ng/mL: Subtherapeutic; medication may not be effective • 0.5-2.0 ng/mL: Therapeutic range; appropriate digoxin level for most patients • Above 2.0 ng/mL: Toxic levels; increased risk of adverse effects • Greater than 3.0 ng/mL: Potentially life-threatening toxicity
- Clinical Significance: Normal results indicate digoxin is at appropriate therapeutic levels. Abnormal results suggest either insufficient medication effect (low levels) or potential toxicity (high levels) requiring dose adjustment
Interpretation
- Low Levels (Below 0.5 ng/mL): Indicates subtherapeutic concentration; may require dose increase; patient may not receive full therapeutic benefit for heart failure or arrhythmia control; assess medication compliance and absorption issues
- Therapeutic Levels (0.5-2.0 ng/mL): Optimal medication effect for positive inotropic and rate-controlling actions; appropriate balance between efficacy and safety; continue current dose with periodic monitoring
- Toxic Levels (Above 2.0 ng/mL): Increased risk of adverse effects including nausea, vomiting, cardiac arrhythmias, visual disturbances, and CNS symptoms; dose reduction typically required; severe toxicity may require digoxin-specific antibody (Digibind) treatment
- Factors Affecting Results: • Renal function: Decreased GFR increases levels • Electrolyte abnormalities: Low potassium, magnesium, or calcium increase toxicity risk • Drug interactions: Quinidine, amiodarone, verapamil increase levels • Age: Elderly patients have higher toxicity risk • Body weight: Dosing based on lean body weight • Gastrointestinal absorption: Varies with GI conditions
- Timing of Sample Collection: Sample should be drawn at least 6-8 hours after dose (preferably 12-24 hours) to allow distribution into tissues and achieve accurate therapeutic level assessment
Associated Organs
- Primary Organ Systems: Cardiovascular system (heart); secondary effects on kidneys, gastrointestinal tract, and nervous system
- Conditions Associated with Abnormal Results: • Heart failure (systolic or diastolic) • Atrial fibrillation and other supraventricular arrhythmias • Acute coronary syndrome • Chronic kidney disease • Thyroid disorders • Electrolyte disturbances (hypokalemia, hypomagnesemia) • Hepatic dysfunction
- Potential Complications of Toxicity: • Cardiac arrhythmias: Premature ventricular contractions, ventricular tachycardia, complete heart block • Gastrointestinal: Nausea, vomiting, anorexia, diarrhea • Visual disturbances: Blurred vision, yellow-tinted vision, scotomas • Neurological: Confusion, headache, weakness, muscle pain • Severe toxicity: Potentially fatal arrhythmias requiring emergency intervention
- High-Risk Populations: Elderly patients, those with renal impairment, hyperthyroidism, acute MI, or concurrent use of interacting medications
Follow-up Tests
- Recommended Monitoring Tests: • Serum electrolytes: Potassium, magnesium, calcium • Renal function panel: Creatinine, BUN, eGFR • Electrocardiogram (ECG): To assess for arrhythmias or toxicity signs • Thyroid function: TSH (if symptoms suggest thyroid disease) • Complete metabolic panel: Comprehensive assessment • Liver function tests: If hepatic disease suspected
- Monitoring Frequency: • Initial: 5-7 days after starting therapy to reach steady state • Routine: Every 6-12 months in stable patients • After dose changes: 1-2 weeks to reach new steady state • If toxicity suspected: Immediately • With medication changes: Within 1-2 weeks • Renal dysfunction patients: More frequent monitoring
- Further Investigations: Echocardiogram to assess cardiac function; stress testing if clinically indicated; chest X-ray for heart size and pulmonary congestion assessment
- When Toxicity Suspected: Stat digoxin level, immediate ECG, electrolyte panel, renal function, consider digoxin-specific antibody testing, continuous cardiac monitoring
Fasting Required?
- Fasting Status: NO - Fasting is not required for digoxin testing
- Sample Collection Timing: Blood sample should be drawn 6-8 hours after digoxin dose (preferably 12-24 hours) to allow adequate tissue distribution and achieve accurate serum concentration measurement at steady state
- Medications to Continue: Patient should continue taking digoxin as prescribed; do not skip dose before test unless specifically instructed by physician
- Other Special Instructions: • Inform laboratory and physician of all current medications, especially those that interact with digoxin • Document exact time of last digoxin dose • Report any recent dose changes or missed doses • Note time of blood draw for accurate interpretation • Disclose any recent illness or changes in renal function • Mention any symptoms suggesting toxicity (nausea, palpitations, vision changes) • Routine arm position: Seated for 5 minutes before collection

How our test process works!