Sign in →

Test Code MISC2MAYO21OH 21-Hydroxylase Antibodies, Serum

Ordering Guidance

Testing for auto-antibodies against 21-hydroxylase is recommended following confirmation of adrenal insufficiency to help differentiate between causes of primary adrenal insufficiency

Shipping Instructions

Ship serum specimen frozen

Specimen Required

Collection Container/Tube: 

Preferred: Red top

Acceptable: Serum gel

Submission Container/Tube: Plastic vial

Specimen Volume: 1 mL

Collection Instructions: Centrifuge and aliquot serum into plastic vial to remove from cells or gel prior to shipping.

Secondary ID


Useful For

Investigation of adrenal insufficiency


Aid in the detection of those at risk of developing autoimmune adrenal failure in the future

Method Name

Enzyme-linked Immunosorbent Assay (ELISA)

Reporting Name

21-Hydroxylase Ab, S

Specimen Type


Specimen Minimum Volume

0.20 mL

Specimen Stability Information

Specimen Type Temperature Time Special Container
Serum Frozen 14 days

Reject Due To

Gross hemolysis Reject
Gross lipemia Reject
Gross icterus OK

Clinical Information

Adrenal insufficiency is caused by failure of the adrenal cortex to produce cortisol. This failure can result from loss of function of the adrenal glands (ie, primary adrenal insufficiency). This is most frequently caused by autoimmune adrenalitis or Addison disease accounting for 68% to 94% of cases. It can occur sporadically or in combination with other autoimmune endocrine diseases that together comprise Type I or Type II autoimmune polyglandular syndrome (APS).


Antibodies that react with several steroidogenic enzymes (most often 21-hydroxylase) are present in the serum of up to 86% of patients with autoimmune primary adrenal insufficiency, but only rarely in patients with other causes of adrenal insufficiency. Therefore, anti-21-hydroxylase autoantibodies (21-OH Abs) are markers of autoimmune Addison disease, whether it’s present alone, or as part of Type I or Type II APS. The measurement of 21-OH Abs is an important step in the investigation of adrenal insufficiency, and may also aid in the detection of those at risk of developing autoimmune adrenal failure in the future.

Reference Values



This is a qualitative test. A positive result indicates the presence of autoantibodies to 21-hydroxylase and is consistent with Addison disease.


Utilizing an index value of <45 as a negative cutoff, this assay has a clinical sensitivity and specificity of 87.0% (95% CI: 79.4%-92.2%) and 99.3% (95% CI: 97.5%-99.8%), respectively.

Method Description

A reference preparation, controls, and patient specimens are incubated with a reaction enhancer overnight in a coated ELISA plate. 21-Hydroxylase (21-OH) antibodies (Ab) act divalently and form a bridge between 21-OH Ab coated on ELISA plate wells and liquid phase 21-OH biotin. The resulting antigen-antibody-antigen complexes are then detected by the addition of streptavidin peroxidase (SA-POD) and tetramethylbenzidine (TMB) to produce a colorogenic reaction. Stop solution is added to halt the reaction and absorbance is read using an ELISA plate reader. The absorbance of each well is directly proportional to the amount of antibody present. Positive and negative determinations are based on index values. Index values are calculated from the mean value of duplicate sample wells and compared to a reference value.(Package insert: 21-Hydroxylase Autoantibody (21-OHAb) ELISA Kit, Kronus, Star, ID. 01/2019)

Day(s) Performed


Report Available

3 to 9 days

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.

CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
21OH 21-Hydroxylase Ab, S 85363-0


Result ID Test Result Name Result LOINC Value
607788 21-Hydroxylase Ab, S 85363-0