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22409 Carbamazepine, Free, Serum (CARF)

Carbamazepine, Free, Serum (CARF)
Test Code: CARFREE
Useful For

​Monitoring carbamazepine (free) therapy in uremic patients

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.

Specimen Requirements
Specimen Type Preferred Container/Tube Acceptable Container/Tube Specimen Volume Specimen Minimum Volume
(allows for 1 repeat)		 Pediatric Minimum Volume
(no repeat)
Serum​ ​Red Top Tube (RTT) ​ ​2 mL ​1 mL ​
Collection Processing Instructions
Red Top Tubes should be centrifuged and aliquoted within 2 hours of collection.
Specimen Stability Information
Specimen Type Temperature Time
​Serum ​
Ambient 
 48 hours
Refrigerated (preferred) 7 days
​Frozen ​28 days
Rejection Criteria
Serum Separator Tube (SST)
​Gross Hemolysis
Performing Laboratory Information
Performing Location Day(s) Test Performed Report Available Methodology/Instrumentation
Mayo Clinic Laboratories​ Monday through Sunday ​1 day
Ultrafiltration followed by Homogeneous Microparticle Agglutination Immunoassay
Reference Lab
Mayo Clinic Laboratories
Reference Range Information
Performing Location Reference Range
Mayo Clinic Laboratories
Therapeutic concentration: 1.0-3.0 mcg/mL
Critical value: > or =4.0 mcg/mL
Interpretation

In patients with normal renal 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, the carbamazepine that circulates in blood is 75% 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. They are best used as a guide in dose adjustment.

Outreach CPTs
CPT Modifier
(if needed)		 Quantity Description Comments
​80157 ​ ​ ​ ​
Ordering Applications
Ordering Application Description
​Centricity ​Carbamazepine, Free
​Cerner ​Carbamazepine Level Free (20)
If the ordering application you are looking for is not listed, contact your local laboratory for assistance.
Specimen Requirements
Specimen Type Preferred Container/Tube Acceptable Container/Tube Specimen Volume Specimen Minimum Volume
(allows for 1 repeat)		 Pediatric Minimum Volume
(no repeat)
Serum​ ​Red Top Tube (RTT) ​ ​2 mL ​1 mL ​
Collection Processing
Red Top Tubes should be centrifuged and aliquoted within 2 hours of collection.
Specimen Stability Information
Specimen Type Temperature Time
​Serum ​
Ambient 
 48 hours
Refrigerated (preferred) 7 days
​Frozen ​28 days
Rejection Criteria
Serum Separator Tube (SST)
​Gross Hemolysis
Useful For

​Monitoring carbamazepine (free) therapy in uremic patients

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.

Reference Range Information
Performing Location Reference Range
Mayo Clinic Laboratories
Therapeutic concentration: 1.0-3.0 mcg/mL
Critical value: > or =4.0 mcg/mL
Interpretation

In patients with normal renal 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, the carbamazepine that circulates in blood is 75% 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. They are best used as a guide in dose adjustment.

For more information visit:
Performing Laboratory Information
Performing Location Day(s) Test Performed Report Available Methodology/Instrumentation
Mayo Clinic Laboratories​ Monday through Sunday ​1 day
Ultrafiltration followed by Homogeneous Microparticle Agglutination Immunoassay
Reference Lab
Mayo Clinic Laboratories
For billing questions, see Contacts
Outreach CPTs
CPT Modifier
(if needed)		 Quantity Description Comments
​80157 ​ ​ ​ ​
For most current information refer to the Marshfield Laboratory online reference manual.