Tacrolimus by Immunoassay

CPT Code(s):
80197

Turnaround Time:
24 hours

Specimen Requirements

Preferred Specimen:
Whole Blood

Minimum Volume:
1.0 mL

Transport Container:
Lavender Top, (EDTA)

Transport Temperature:
Room Temperature

Collection Instructions:
Whole blood collected in Lavender Top, (EDTA) tube.

Rejection Criteria:
Serum or Plasma specimen submitted. Specimens submitted in incorrect tube or specimens centrifuged prior to submission. Unlableled specimens or specimens submitted past listed stability.

Stability Criteria

Room Temperature:
5 days

Refrigerated:
7 days

Frozen:
30 days

Clinical Significance

Tacrolimus is an immunosuppressive medication primarily used after organ transplantation to lower the risk of organ rejection. It works by inhibiting calcineurin, which reduces the activity of T-cells, crucial players in the immune response. Here are some key points regarding its clinical significance:

Prevention of Organ Rejection:

Kidney Transplantation: Tacrolimus is widely used to prevent kidney rejection. It is often part of a triple-drug regimen that includes a corticosteroid and another immunosuppressant.

Liver Transplantation: It is also used in liver transplant patients to prevent rejection.

Heart and Lung Transplantation: Tacrolimus can be employed in heart and lung transplants, although it is less common compared to kidney and liver transplants.

Treatment of Autoimmune Diseases:

Rheumatoid Arthritis: Tacrolimus can be used off-label for the treatment of severe rheumatoid arthritis.

Dermatological Conditions: Topical formulations of tacrolimus are used to treat eczema (atopic dermatitis) and other skin conditions.

Mechanism of Action:

Tacrolimus inhibits calcineurin, which is necessary for the activation of T-cells. This inhibition prevents the production of interleukin-2 (IL-2), a cytokine that is crucial for T-cell proliferation.

By reducing T-cell activity, tacrolimus lowers the immune response, thereby reducing the risk of organ rejection or autoimmune attacks.

Pharmacokinetics:

Absorption: Tacrolimus is variably absorbed when taken orally. Food can affect its absorption, so it is recommended to take it consistently with or without food.

Metabolism: It is metabolized in the liver by the cytochrome P450 3A enzyme system (CYP3A).

Excretion: The drug is excreted mainly via the bile and feces, with minimal renal excretion.

Side Effects:

Nephrotoxicity: Tacrolimus can cause kidney damage, which necessitates regular monitoring of kidney function.

Neurotoxicity: Patients may experience tremors, headaches, and other neurological symptoms.

Hyperglycemia and Diabetes: Tacrolimus can induce diabetes, especially in patients who are already at risk.

Infections: Due to its immunosuppressive effects, tacrolimus increases the risk of infections.

Monitoring:

Blood Levels: Regular monitoring of blood levels of tacrolimus is essential to ensure therapeutic levels and to avoid toxicity.

Kidney and Liver Function: Monitoring kidney and liver function is critical due to the potential nephrotoxic and hepatotoxic effects of the drug.

Blood Pressure and Blood Sugar: Patients on tacrolimus should have regular monitoring of blood pressure and blood sugar levels.

Drug Interactions:

Tacrolimus interacts with several drugs, particularly those that affect the CYP3A enzyme system. Examples include certain antibiotics, antifungals, and other immunosuppressants.

Caution is required when prescribing other medications alongside tacrolimus to avoid adverse interactions.

Conclusion:

Tacrolimus plays a crucial role in the management of transplant patients and certain autoimmune diseases. Its effectiveness in preventing organ rejection has made it a cornerstone in transplant medicine. However, its use requires careful monitoring due to its potential side effects and interactions with other medications.