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EPIC CODE: LAB2861 21-Hydroxylase Antibodies, Serum

Additional Codes

Sunquest Code:     HYDSAM
Mayo Lab Code:     21OH

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

Investigating adrenal insufficiency


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


Addison disease is the most frequent cause of primary adrenal insufficiency.


Auto-antibodies against 21-hydroxylase are present in up to 90% of Addison disease cases.


Measurement of anti-21-hydroxylase auto-antibodies is useful in the evaluation of the cause of established primary adrenal insufficiency.

Method Name

Enzyme-linked Immunosorbent Assay (ELISA)

Reporting Name

21-Hydroxylase Ab, S

Specimen Type


Specimen Minimum Volume

0.2 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 Reject

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 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 II APS. The measurement of 21-OH Abs is an important step in the investigation of adrenal insufficiency and may 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.


Lipemic or grossly hemolyzed serum should not be used in this assay.


Results should be interpreted in the context of clinical symptoms and adrenal functional confirmatory tests.


In rare cases, some individuals can develop antibodies to mouse or other animal antibodies (often referred to as human anti-mouse antibodies [HAMA] or heterophile antibodies), which may cause interference in some immunoassays. Caution should be used in interpretation of results and the laboratory should be alerted if the result does not correlate with the clinical presentation.

Clinical Reference

1. Charmandari E, Nicolaides NC, Chrousos GP: Adrenal insufficiency. Lancet. 2014 Jun 21;383(9935):2152-2167

2. Bancos I, Hahner S, Tomlinson J, Arlt W: Diagnosis and management of adrenal insufficiency. Lancet Diabetes Endocrinol. 2015 Mar;3(3):216-226

3. Bornstein SR, Allolio B, Arlt W, et al: Diagnosis and treatment of primary adrenal insufficiency: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab. 2016 Feb;101(2):364-389

Method Description

A reference preparation, controls, and patient specimens are incubated with a reaction enhancer overnight in a coated enzyme-linked immunosorbent assay (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 and tetramethylbenzidine 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; 01/2019)

Day(s) Performed


Report Available

3 to 9 days

Specimen Retention Time

3 months

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

NY State Approved