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Test Code CARF Carbamazepine, Free, Serum

Reporting Name

Carbamazepine, Free, S

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Useful For

Monitoring unbound or free carbamazepine levels in patients where the total carbamazepine result is within the therapeutic range, but the patient is experiencing side effects

 

Monitoring carbamazepine (free) therapy in patients who are uremic

Method Name

Ultrafiltration followed by Homogeneous Microparticle Agglutination Immunoassay


Specimen Required


Collection 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 Type

Serum Red

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

Reject Due To

Gross hemolysis Reject

Reference Values

Therapeutic concentration: 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 above 1.0 mcg/mL, and toxicity may occur when the free carbamazepine is greater than or equal to 4.0 mcg/mL.

 

Under normal circumstances, 75% of the carbamazepine that circulates in blood is protein-bound. Therapies or conditions such as uremia that displace carbamazepine from protein cause a higher free (unbound) fraction of the drug circulating in blood. In uremia, 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 carbamazepine levels. Toxicity may occur 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. Serum levels are best used as a guide in dose adjustment.

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

80157

LOINC Code Information

Test ID Test Order Name Order LOINC Value
CARF Carbamazepine, Free, S 3433-0

 

Result ID Test Result Name Result LOINC Value
CARF Carbamazepine, Free, S 3433-0

Forms

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