IGAS - Clinical: IgA Subclasses, Serum

Test Catalog

Test Name

Test ID: IGAS    
IgA Subclasses, Serum

Useful For Suggests clinical disorders or settings where the test may be helpful

Investigation of immune deficiency due to IgA2 deficiency


Evaluating patients with anaphylactic transfusion reactions


Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

IgA, the predominant immunoglobulin secreted at mucosal surfaces, consists of 2 subclasses, IgA1 and IgA2. IgA1 is the major (approximately 80%) subclass in serum. IgA2 is the major subclass in secretions such as milk. Although IgA deficiency is a common defect (1 in 700), it is usually asymptomatic. IgA deficiency with or without IgG subclass deficiency, however, can lead to recurrent pulmonary and gastrointestinal infections. Some infections (eg, recurrent sinopulmonary infections with Haemophilus influenzae) may be related to a deficiency of IgA2 in the presence of normal total IgA concentrations.


Paradoxically, bacterial infections may also cause IgA deficiency. For example, IgA1 (but not IgA2) can be cleaved and inactivated by certain bacteria, thus depleting the majority of the IgA. In the presence of a concurrent IgA2 deficiency, infection by these organisms results in an apparent IgA deficiency.


IgA deficiency is 1 cause of anaphylactic transfusion reactions. In these situations, IgA-deficient patients produce anti-IgA antibodies that react with IgA present in the transfusion product. While transfusion reactions typically occur in patients who have no detectable levels of IgA, they can occur in patients with measurable IgA. In these situations, the complete deficiency of 1 of the IgA subclasses may be the cause of the transfusion reactions.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.


0-<5 months: 7-37 mg/dL

5-<9 months: 16-50 mg/dL

9-<15 months: 27-66 mg/dL

15-<24 months: 36-79 mg/dL

2-<4 years: 27-246 mg/dL

4-<7 years: 29-256 mg/dL

7-<10 years: 34-274 mg/dL

10-<13 years: 42-295 mg/dL

13-<16 years: 52-319 mg/dL

16-<18 years: 60-337 mg/dL

> or =18 years: 61-356 mg/dL



0-<5 months: 10-34 mg/dL

5-<9 months: 14-41 mg/dL

9-<15 months: 20-50 mg/dL

15-<24 months: 24-58 mg/dL

2-<4 years: 16-162 mg/dL

4-<7 years: 17-187 mg/dL

7-<10 years: 21-221 mg/dL

10-<13 years: 27-250 mg/dL

13-<16 years: 36-275 mg/dL

16-<18 years: 44-289 mg/dL

> or =18 years: 50-314 mg/dL



0-<5 months: 0.4-5.5 mg/dL

5-<9 months: 1.5-6.2 mg/dL

9-<15 months: 2.8-7.0 mg/dL

15-<24 months: 3.9-7.7 mg/dL

2-<4 years: 1.3-31.1 mg/dL

4-<7 years: 1.1-39.1 mg/dL

7-<10 years: 1.4-48.0 mg/dL

10-<13 years: 2.6-53.4 mg/dL

13-<16 years:  4.7-55.1 mg/dL

16-<18 years: 6.6-54.3 mg/dL

> or =18 years: 9.7-156.0 mg/dL

Interpretation Provides information to assist in interpretation of the test results

Low concentrations of IgA2 with normal IgA1 levels suggest an IgA2 deficiency.


Elevated concentrations of IgA2 with normal or low amounts of IgA1 suggest a clonal plasma cell proliferative disorder secreting a monoclonal IgA2.


Increased total IgA levels also may be seen in benign disorders (eg, infection, inflammation, allergy), hyper IgD syndrome with periodic fever and monoclonal gammopathies (eg, myeloma, monoclonal gammopathies of undetermined significance [MGUS]).

Clinical Reference Recommendations for in-depth reading of a clinical nature

1. Schauer U, Stemberg F, Rieger CHL, et al: Establishment of age-dependent reference values for IgA subclasses. Clin Chim Acta 2003;328:129-133

2. Saulsbury FT: Hyperimmunoglobulinemia D and periodic fever syndrome (HIDS) in a child with normal serum IgD, but increased serum IgA concentration. J Pediatrics 2003:127-129

3. Popovsky MA: Transfusion Reactions. American Association of Blood Banks, Third edition, 2007