Sign in →

Epic Code LAB848 5-Flucytosine, Serum

Important Note

Order as Reference Miscellaneous #LAB848; indicate complete test name when ordering.

Additional Codes

Mayo Code: FLUC

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Useful For

Monitoring serum concentration during therapy

 

Evaluating potential toxicity

 

May aid in evaluating patient compliance

Specimen Type

Serum


Specimen Required


Collection Container/Tube:

Preferred: Red top

Acceptable: Serum gel

Submission Container/Tube: Plastic vial

Specimen Volume: 0.5 mL

Collection Instructions:

1. Serum for a peak level should be collected 1 to 2 hours after oral dose or 30 minutes after intravenous infusion. Trough specimens should be collected immediately prior to next scheduled dose.

2. Centrifuge and aliquot serum to plastic vial within 2 hours of collection.


Laboratory Test Directory Note:

COLLECTION NOTE: Volumes listed are in serum or plasma, draw approximately 2 1/2 times the requested volume in whole blood.

Specimen Minimum Volume

0.3 mL

Forms

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

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Refrigerated (preferred) 28 days
  Ambient  28 days
  Frozen  28 days

Reject Due To

Gross hemolysis OK
Gross lipemia OK
Gross icterus OK

Cautions

This test cannot be performed on whole blood. Serum must be separated from cells within 2 hours of collection.

Clinical Information

Flucytosine is a broad-spectrum antifungal agent generally used in combined therapy (often with amphotericin B) for treatment of fungal infections such as cryptococcal meningitis. Concerns with toxicity (ie, bone marrow suppression, hepatic dysfunction) and development of fungal resistance limit the use of flucytosine, particularly as a monotherapy. The drug is well-absorbed orally but can also be administered intravenously (available outside of the United States).

 

There is good correlation between serum concentrations of flucytosine with both efficacy and risk for toxicity. Because of the drug's short half-life (3-6 hours), therapeutic monitoring is typically performed at peak levels approximately 2 hours after an oral dose or 30 minutes after an intravenous administration.

 

Flucytosine is eliminated primarily as unmetabolized drug in urine. Patients with kidney dysfunction may require dose adjustments or more frequent monitoring to ensure that serum concentrations do not accumulate to excessive levels. Nephrotoxicity associated with use of amphotericin B can affect elimination of flucytosine when the drugs are coadministered.

Method Name

Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Report Available

3 to 8 days

Reporting Name

5-Flucytosine, S

Reference Values

Therapeutic concentration:

Peak >25.0 mcg/mL (difficult infections may require higher concentrations)

Toxic concentration:

Peak >100.0 mcg/mL

Interpretation

Most individuals display optimal response to flucytosine when peak serum levels (1-2 hours after oral dosing) are greater than 25.0 mcg/mL. Some infections may require higher concentrations for efficacy. Toxicity is more likely when peak serum concentrations are greater than 100.0 mcg/mL

Method Description

5-Flucytosine is extracted by mixing serum samples with an acetonitrile and methanol mixture to precipitate proteins. The supernatant is removed and analyzed by an in-house developed liquid chromatography-tandem mass spectrometry method.(Unpublished Mayo method)

Day(s) Performed

Tuesday, Thursday

Clinical Reference

1. Rifai N, Horvath AR, Wittwer CT, eds: Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 6th ed. Elsevier; 2018

2. Goodwin ML, Drew RH: Antifungal serum concentration monitoring: an update. J Antimicrob Chemother. 2008 Jan;61(1):17-25. doi: 10.1093/jac/dkm389

3. Andes D, Pascual A, Marchetti O: Antifungal therapeutic drug monitoring: established and emerging indications. Antimicrob Agents Chemother. 2009 Jan;53(1):24-34. doi: 10.1128/AAC.00705-08

Test Classification

This test was developed, and its performance characteristics 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

80299

LOINC Code Information

Test ID Test Order Name Order LOINC Value
FLUC 5-Flucytosine, S 3639-2

 

Result ID Test Result Name Result LOINC Value
82741 5-Flucytosine, S 3639-2