Posted Date
Effective Date
Test Name Dexamethasone
Update Type Replacement Test
Order Code FDXM


Order Code:                  FDXM

Fee Code:                     AA389 (CPT 80375)

Reference Laboratory:   Mayo FDXM (Esoterix Endocrinology 500140)


New Order Code:          DEXA

New Fee Code:             AB046 (CPT 80299)

New Reference Lab:      Mayo DEXA


Mayo Clinic Laboratories will begin offering Dexamethasone by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) (test ID DEXA) effective May 12, 2022. This test will replace test ID FDXM forwarded to Esoterix Endocrinology.


Collection Instructions: Draw blood between 7:30 a.m. and 9:00 a.m. the morning following an evening dose. Collect specimen in a red top (preferred) or SST tube.  Centrifuge, aliquot 2 mL (minimum 0.6 mL) of serum into a plastic vial within one hour of collection, and refrigerate up to 7 days or freeze for longer storage.


Reference Range:

Baseline: <30 ng/dL

8:00 a.m. following 1 mg Dexamethasone, previous evening: >100 ng/dL

8:00 a.m. following 8 mg Dexamethasone, (4 x 2 mg doses) previous day: >800 ng/dL