Immunoglobulin M (IgM)

Sample

1. Fresh serum of the patient is needed.
2. Analyze the sample as soon as possible or can store at 4 °C for a few hours (less than 72 hours).
3. The sample is stable at -20 °C for 6 months.

Indications

1. Used to detect monoclonal gammopathy.
2. It is advised in immune deficiencies.

Pathophysiology

1. IgM exists in two form 
2.     Monomeric IgM form exists as a B- cell receptor for antigen.

3.   Pentameric IgM form is present in the blood. These five basic units are joined by the J-chain.
   

   IgM Molecular Structure

4. It is 10 % of the total immunoglobulin with a molecular weight of 900,000 and is 19 S.
   1. Its concentration is 120 mg/dl.
   2. Its molecular weight is 900,000 and 19S.
5. There are 10 potential sites for antigen binding.
6. IgM is the first antibody production in response to antigenic stimulation called Primary immune response.
   1. In primary response, there is the stimulation of B-Lymphocytes which form the plasma cells and produce IgM.
7. IgM as a pentamer form is the most effective stimulator of the complement system for a lytic reaction.
8. In fetal life, this is the first immunoglobulin which appears first and its raised level in neonate indicates intrauterine infection.
9. IgM has a half-life of 10 days.
10. It is predominantly present in the intravascular spaces.
11. It is a poor toxin neutralizing antibody.

Normal Level

Source 1

Age	mg/dL
Cord blood	<25
one month	20 to 80
2 to 5 month	25 to 100
6 to 9 month	35 to 125
10 to 12 month	40 to 150
1 to 8 year	45 to 200
9 to 12 year	50 to 250
>12 year	50 to 300

• To convert into SI unit x 10 = mg/L

Source 2

• Adult = 55 to 375 mg/dL
• Children = 20 to 200 mg/dL

Another source

1. 0 to <5 months = 26 to 122 mg/d
2. 15 to <24 months = 46 to 152 mg/dL
3. 2 to <4 years = 37 to 184 mg/d
4. 10 to <13 years = 41 to 255 mg/dL
5. 16 to <18 years =  49 to 201 mg/dL
6. More than 18 years = 37 to 286 mg/dL
   1. Values vary from different methodology.

Decreased level of IgM seen in:

• Decreased level seen in congenital deficiency diseases.

Increased level of IgM seen in :

1. Elevations of IgM may be due to polyclonal immunoglobulin production which was seen in various infections.
2. An isolated increase in IgM level may be seen in viral infections e.g. Viral hepatitis, infectious mononucleosis, and early response to bacterial or parasitic infection.
3. Increased levels of IgM may be seen in Rheumatoid arthritis, biliary cirrhosis, and some other chronic disorders.
4. Raised levels are also seen in Hyper IgM dysgammaglobulinemia, active sarcoidosis, collagen vascular diseases, nephrotic syndrome.
5. Monoclonal  raised levels are seen in :
   1. Waldenstrom’s globulinemia.
   2. Lymphomas.

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