Lab Test

Hydroxylase Antibody, 21

21-Hydroxylase, 21-OH Ab, Adrenal antibody , ARUP #70265, EPIC: LAB7121, SOFT: X21HO

Specimen Collection Criteria

Collect (preferred specimen): One plain Red-top tube.

Also acceptable: One Gold-top SST tube.

  • Send specimen for processing immediately afte collection.
  • Separate samples must be submitted when multiple test are ordered.

Physician Office/Drawsite Specimen Preparation

Let specimen clot 30-60 minutes then immediately centrifuge to separate serum from cells.  Transport serum to a plastic transport tube and refrigerate (2-8°C or 36-46°F).

Preparation for Courier Transport

Transport: 1.0mL serum, refrigerated (2-8°C or 36-46°F) (Min: 0.2mL)

Rejection Criteria

  • Hemolyzed specimens.
  • Specimens not collected and processed as indicated.



Results available in 3-10 days.

Reference Range

0.0-1.0 U/mL.

Test Methodology

Semi-Quantitative Radioimmunoassay.


A value greater than 1.0 Kronus Units/mL is considered positive for 21-OH Antibody. Kronus units are arbitary. Kronus Units = U/mL.

The 21-Hydroxylase Antibody assay is intended for the semi-quantitative determination of anitbodies to steroid 21-hydroxylase in human serum.

The presence of antibodies to 21-hydroxylase (greater than 1.0 U/mL) is indicative of primary adrenal insufficiency (Addison disease). Results should be interpreted in the context of clinical symptoms including functional adrenal testing.

In males with adrenal insufficiency and 21-hydroxylase antibodies within the reference interval (less than 1.0 U/mL), X-Linked Adrenoleukodystrophy (X-ALD) should be excluded by using Very Long-Chain Branched Fatty Acids in plasma (ARUP Test Code 2004250) for screening..

CPT Code


Test Codes

ARUP #70265, EPIC: LAB7121, SOFT: X21HO

Last Updated


Microtainer® and Vacutainer® are registered trademarks of Becton, Dickinson and Company.
UroVysion® is a registered trademark of Abbott Laboratories. ThinPrep® is a registered trademark of Hologic, Incorporated.


This directory currently reflects information only for specimens collected and/or processed at the
Farmington Hills, Grosse Pointe, Royal Oak, and Troy campuses.