IgA in serum

Reference interval

Table

age	MEAN mg/dL	RANGE mg/dL
Adult	225.5	69-382
CORD BLOOD	2.3	1.4-3.6
1 month	13	1.3-53
2 months	15	2.8-47
3 months	17	4.6-46
4 months	23	4.4-73
5 months	31	8.1-84
6 months	25	8.1-68
7-9 months	36	11-90
10-12 months	40	16-84
1 year	44	14-106
2 years	47	14-123
3 years	66	22-159
4-5 years	68	25-154
6-8 years	90	33-202
9-10 years	113	45-236

Principle

• see IgA in serum/CSF/urine

Clinical significance

Approximately 10-15% of serum Ig is IgA.

An important form of IgA is called secretory IgA. It is found in tears, sweat, saliva, milk, & colostrum, & in gastrointestinal and bronchial secretions. Secretory IgA has a M.W. of 380 kD & consists of two molecules of IgA & a secretory component.

The secretory component makes secretory IgA more resistant to enzymes & protects the mucosa from bacteria & viruses. Its presence in colostrum & milk probably protects the newborn from intestinal infections. IgA can activate complement by the alternative pathway but the exact role of IgA in serum is not clear.

Reference ranges for IgG & IgM in various human adult populations differ around the world because levels depend on the extent of antigenic stimulation coming from the environment. IgA levels, however, are unaffected by environmental factors. Immunoglobulin synthesis is stimulated by environmental antigens so that serum IgA reaches adult levels in about 14 years. IgA in saliva, however, reaches adult levels in about 6 weeks.

Polyclonal increases in serum Igs are the normal response to infections. IgA tends to predominate in skin, gut, respiratory, & renal infections. Chronic bacterial infections cause an increase in serum levels of all Igs. Individual Igs are of value, in the differential diagnosis of liver disease & of intrauterine infections.

Should a paraprotein be identified in blood, or urine, or both, its heavy & light chains should be typed & the concentrations of polyclonal IgG, IgA, & IgM should be determined. These studies confirm whether the spike on the electrophoretic pattern is indeed a paraprotein; they help to decide the probable prognosis, & they show whether the polyclonal Igs are so low as to make the patient vulnerable to infections. Prognosis is based on the class of the paraprotein found, its concentration at the time of diagnosis, & the rate at which its concentration increases. The concentration at the time of diagnosis must correlate with the current extent of the disease process. The rate of increase in concentration, when compared with the average doubling time for the concentration of the particular class of paraprotein, should correlate with the rate of growth of the neoplasm.

Increases

• isolated increases in serum IgA:
  • skin infections & inflammatory disorders of skin
    • acute leukocytoclastic vasculitis
  • respiratory infections
  • gastrointestinal infections
  • kidney infections

Specimen

• 200 uL
• store sample in freezer until ready for assay
• highly lipemic samples may result in inaccurate determination & should be redrawn on a fasting patient
• plasma is not recommended
• see IgA in serum/CSF/urine

More general terms

• IgA in body fluid

More specific terms

• IgA secretory in serum/plasma
• IgA subclass 1 in serum
• IgA subclass 2 in serum

Additional terms

• immunoglobulin-A (IgA)
• nephelometry

Component of

• immunoglobulin classes in serum (gammaglobulin classes in serum)