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Test ID: CARFT Carbamazepine, Free and Total, Serum

Useful For

Monitoring carbamazepine (free and total) therapy in patients who are uremic

Profile Information

Test ID Reporting Name Available Separately Always Performed
CARTA Carbamazepine, Tot, S Yes Yes
CARF Carbamazepine, Free, S Yes Yes

Method Name

CARF: Ultrafiltration Followed by Homogeneous Microparticle Agglutination Immunoassay

CARTA: Homogeneous Microparticle Agglutination Immunoassay

Reporting Name

Carbamazepine, Free and Total, S

Specimen Type

Serum Red


Specimen Required


Container/Tube: Red top (serum gel/SST are not acceptable)

Submission Container/Tube: Plastic vial

Specimen Volume: 2 mL

Collection Instructions: Centrifuge and aliquot serum into a plastic vial within 2 hours of collection.


Specimen Minimum Volume

1 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Red Refrigerated (preferred) 7 days
  Frozen  28 days
  Ambient  48 hours

Clinical Information

Carbamazepine (Tegretol) is an effective treatment for complex partial seizures, with or without generalization to tonic-clonic seizures. It is frequently administered in conjunction with other antiepileptic agents, such as phenytoin and valproic acid.

 

Under normal circumstances, 75% of the carbamazepine that circulates in blood is protein bound. In severe uremia, carbamazepine may be displaced from protein, resulting in a higher free (unbound) fraction of the drug circulating in blood. Since neurologic activity and toxicity are directly related to the circulating free fraction of drug, adjustment of dosage based on knowledge of the free carbamazepine level may be useful in patients with severe uremia.

Reference Values

CARBAMAZEPINE, TOTAL

Therapeutic: 4.0-12.0 mcg/mL

Critical value: ≥15.0 mcg/mL

 

CARBAMAZEPINE, FREE

Therapeutic: 1.0-3.0 mcg/mL

Critical value: ≥4.0 mcg/mL

Interpretation

In patients with normal kidney function, optimal response is often associated with free (unbound) carbamazepine levels greater than 1.0 mcg/mL, and toxicity may occur when the free carbamazepine is greater than or equal to 4.0 mcg/mL.

 

In uremic patients, the free carbamazepine level may be a more useful guide for dosage adjustments than the total level. In patients with severe uremia, subtherapeutic total carbamazepine levels in the range of 1.0 to 2.0 mcg/mL may be associated with therapeutic free levels. Toxicity may occur in these patients when the free carbamazepine level is greater than or equal to 4.0 mcg/mL (even though the total carbamazepine concentration is <15.0 mcg/mL).

 

As with the serum levels of other anticonvulsant drugs, total and free carbamazepine levels should be correlated with the patient's clinical condition. They are best used as a guide in dose adjustment.

Clinical Reference

1. Svinarov DA, Pippenger CE. Relationships between carbamazepine-diol, carbamazepine-epoxide, and carbamazepine total and free steady-state concentrations in epileptic patients: the influence of age, sex, and comedication. Ther Drug Monit. 1996;18(6):660-665

2. Bernus I, Dickinson RG, Hooper WD, Eadie MJ. The mechanism of the carbamazepine-valproate interactions in humans. Br J Clin Phamacol. 1997;44(1):21-27

3. Dasgupta A, Volk A. Displacement of valproic acid and carbamazepine from protein binding in normal and uremic sera by tolmetin, ibuprofen, and naproxen: presence of inhibitor in uremic serum that blocks valproic acid-naproxen interactions. Ther Drug Monit. 1996;18(3):284-287

4. Moyer TP: Therapeutic drug monitoring. In: Burtis CA, Ashwood ER eds. Tietz Textbook of Clinical Chemistry. 4th ed. WB Saunders Company; 2005: 1237-1285

5. Patsalos PN, Berry DJ, Bourgeois BF, et al. Antiepileptic drugs-best practice guidelines for therapeutic drug monitoring: A position paper by the subcommission on therapeutic drug monitoring, ILAE Commission on Therapeutic Strategies. Epilepsia. 2008;49(7):1239-1276

6. Kanner A.M, Ashman E, Gloss D, et al. Practice guideline update summary: Efficacy and tolerability of the new antiepileptic drugs I: Treatment of new-onset epilepsy Report of the Guideline Development, Dissemination, and Implementation Subcommittee of the American Academy of Neurology and the American Epilepsy Society. Neurology. 2018;91(2):74-81

Day(s) Performed

Monday through Sunday

Report Available

Same day/1 day

Test Classification

This test has been modified from the manufacturer's instructions. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information

80156

80157

LOINC Code Information

Test ID Test Order Name Order LOINC Value
CARFT Carbamazepine, Free and Total, S 34545-4

 

Result ID Test Result Name Result LOINC Value
CARF Carbamazepine, Free, S 3433-0
CARTA Carbamazepine, Tot, S 3432-2

Forms

If not ordering electronically, complete, print, and send a Therapeutics Test Request (T831) with the specimen.

Mayo Clinic Laboratories | Therapeutics Catalog Additional Information:
mml-anticonvulsants