Tacrolimus

Blood

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Drug monitoring test.

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Tacrolimus Test Information Guide

Why is it done?
- Measures the blood concentration of tacrolimus, a potent immunosuppressive drug used to prevent organ rejection in transplant recipients
- Ensures therapeutic drug levels are maintained for optimal immune suppression while minimizing toxicity
- Ordered immediately after transplantation and regularly throughout the patient's lifetime to monitor drug efficacy and safety
- Used in kidney, heart, liver, pancreas, and small bowel transplant recipients
- Performed when patients experience signs of organ rejection or drug toxicity
- Helps guide dose adjustments based on individual patient metabolism and clinical response
Normal Range
- Therapeutic Range: 5-20 ng/mL (nanograms per milliliter), with specific ranges varying by transplant type and time post-transplantation
- Early Post-Transplant (first 3 months): 10-20 ng/mL
- Maintenance Phase (after 3 months): 5-15 ng/mL
- Units of Measurement: ng/mL or ng/L (nanograms per liter); values should be drawn at trough level (immediately before next dose)
- Low Levels (<5 ng/mL): Increased risk of organ rejection and graft failure
- High Levels (>20 ng/mL): Increased risk of drug toxicity including nephrotoxicity, neurotoxicity, and infection
Interpretation
- Within Therapeutic Range (5-20 ng/mL): Optimal balance between immunosuppression and toxicity; continue current dose and recheck at scheduled intervals; range narrows over time post-transplant
- Below Therapeutic Range (<5 ng/mL): Indicates inadequate immunosuppression; dose should be increased; patient at high risk for acute rejection episode; may present with fever, elevated creatinine, or decreased graft function
- Above Therapeutic Range (>20 ng/mL): Indicates potential toxicity; dose should be reduced; may correlate with acute kidney injury, tremors, headaches, or opportunistic infections
- Significantly Elevated (>25 ng/mL): Serious concern for tacrolimus toxicity; immediate dose reduction or discontinuation may be necessary; close monitoring of renal function and neurological status essential
- Factors Affecting Interpretation: Drug interactions (CYP3A4 inducers/inhibitors), hepatic function, gastrointestinal absorption variability, genetic polymorphisms, diet changes, and medication adherence significantly impact levels; specimen collection timing (trough vs peak) critical for accuracy
- Clinical Patterns: Rising levels over time may indicate declining renal function; unexplained level drops suggest medication non-adherence or drug interactions; wide fluctuations indicate absorption problems
Associated Organs
- Primary Target Organs: Transplanted organ (kidney, heart, liver, pancreas, intestine); immune system (T-lymphocytes); kidneys (metabolism and clearance)
- Organs at Risk of Toxicity: Kidneys (tacrolimus nephrotoxicity), liver, nervous system, bone marrow
- Acute Rejection (Inadequate Levels): Transplanted organ shows inflammation and dysfunction; symptoms vary by organ type; may progress to chronic rejection and graft loss if untreated
- Tacrolimus Nephrotoxicity: Elevated creatinine, reduced GFR, acute kidney injury; dose-dependent and time-dependent; may be reversible if caught early and dose reduced
- Neurotoxicity: Tremors, headaches, confusion, seizures, posterior reversible encephalopathy syndrome (PRES); more common at higher levels
- Infection Risk: Excessive immunosuppression from appropriate levels increases bacterial, viral (CMV, BK virus), and fungal infections
- Malignancy Risk: Long-term immunosuppression increases risk of post-transplant lymphoproliferative disorder and skin cancers
Follow-up Tests
- Renal Function Tests: Serum creatinine, blood urea nitrogen (BUN), estimated glomerular filtration rate (eGFR); performed at each tacrolimus level check to monitor for nephrotoxicity
- Hepatic Function Tests: AST, ALT, alkaline phosphatase, total bilirubin; important for drug metabolism and toxicity assessment
- Electrolytes and Minerals: Potassium, magnesium, calcium, phosphorus; tacrolimus can cause hyperkalemia and hypomagnesemia
- Complete Blood Count (CBC): To monitor for bone marrow suppression and infection indicators; assess white blood cell count
- Glucose Testing: Fasting glucose and HbA1c; tacrolimus can cause post-transplant diabetes mellitus
- Viral Serologies: CMV antigenemia or PCR, BK virus PCR; especially if levels fall and rejection suspected or infection concerns arise
- Graft Biopsy: Considered if tacrolimus levels are subtherapeutic and clinical signs of rejection persist; provides histological confirmation of rejection
- Monitoring Schedule: Daily-weekly in first 1-2 weeks, weekly for first month, then monthly for first year, then every 3-6 months for maintenance phase; frequency increases with dose changes or clinical concerns
Fasting Required?
- Fasting Status: No - fasting is NOT required for tacrolimus level testing
- Specimen Timing (Critical): Must draw blood at TROUGH level - immediately before the patient's next scheduled dose (typically in morning before breakfast); do NOT draw randomly or after dose administration
- Patient Instructions: Patient should take tacrolimus dose immediately after blood draw; maintain regular dosing schedule without skipping doses before lab draw; inform lab of exact time of last dose and next scheduled dose
- Food/Drug Interactions: Avoid grapefruit juice and high-fat meals on day of testing as they may alter absorption; do not discontinue any medications without physician approval; notify healthcare provider of all new medications, supplements, or herbal products
- Preparation: Wear comfortable clothing with accessible arms; stay hydrated unless otherwise instructed; bring medication list and transplant clinic appointment card; arrive 5-10 minutes early to coordinate exact timing with blood draw; empty bladder if possible to reduce stress
- Specimen Details: Use EDTA (lavender-top) tube; 2-3 mL of whole blood typically required; specimen must be handled promptly; some labs require specific tube types; check with your facility

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