Isoniazid Drug Level
Label Mnemonic: INH
Epic Lab Code: LAB3451
Downtime Form: A-1a Miscellaneous Request
Commercial Mail-out Laboratory
5231 RCP
Specimen Instructions:
Indicate serum on request form and label specimen appropriately (serum).
Collection Medium:
Red top tube 5 mL (Clot Activator)
Preferred Minimum: 1 mL serum from a red top tube
Absolute Minimum: 0.4 mL serum from a red top tube
Rejection Criteria:
Serum gel tube
Testing Schedule:
Testing is performed once per week at reference laboratory.
Turn Around Time:
4-16 days upon receipt at reference laboratory.
Reference Range:
Usual therapeutic range in the treatment of tuberculosis:
1 - 7 mcg/mL. Toxic symptoms present at approximately 20 mcg/mL and greater.

Isoniazid is known to have limited stability in biological specimens which may be concentration and storage condition dependent. Negative or lower than expected results should be interpreted with caution.
High Performance Liquid Chromatography-Tandem Mass Spectrometry (LC- MS/MS)
CPT Code: