Ordering Recommendation

Monitor levels of antifungal drug, 5-fluorocytosine.

New York DOH Approval Status

This test is New York state approved.

Specimen Required

Patient Preparation

Plain red.

Specimen Preparation

Aseptically remove 2 mL serum to a sterile tube (ARUP supply #43115) and freeze. Available online through eSupply using ARUP Connect™ or contact ARUP Client Services at (800) 522-2787. (Min: 1 mL).

Storage/Transport Temperature


Unacceptable Conditions



Required information includes: time and date of collection, time of last dose, and list of all antibiotics that the patient is receiving or has received in the past 48 hours.


Ambient: 2 hours; Refrigerated: 24 hours; Frozen: 1 week


Quantitative Bioassay




2-3 days

Reference Interval

Interpretive Data

Normal peak serum concentration for 5-fluorocytosine is 30-45 µg/mL with a 2 g PO dose or 60-80 µg/mL with a 100 mg/kg/day PO dose. Trough serum concentration is not well established. Toxicity may be seen with sustained levels greater than 100 µg/mL.

For bioassay measurements, the presence of other antimicrobial agents may interfere with the assay. Other factors that may influence antimicrobial levels include inherent differences among patients and their underlying physical conditions as well as the dose and route of administration of the antimicrobial agent.

Compliance Category



Please include time of last dose, and list of all antibiotics that the patient is receiving or has received in the past 48 hours. This information is important for laboratory handling and essential for subsequent physician interpretation of results. 

Hotline History


CPT Codes



Component Test Code* Component Chart Name LOINC
0060857 Antifungal Level, 5-Fluorocytosine, 5-FC 3639-2
* Component test codes cannot be used to order tests. The information provided here is not sufficient for interface builds; for a complete test mix, please click the sidebar link to access the Interface Map.


  • 5-Flucytosine
  • 5-Flucytosine level
  • 5-Flucytosine, Serum
  • Ancobon serum levels
  • Antimicrobial Assay, 5-Flucytosine
  • Fluorocytosine antifungal level
Antifungal Level, 5-Fluorocytosine (5-FC)