What is the Immunoglobulin M (IgM) test?

The Immunoglobulin M (IgM) test measures the level of IgM antibodies, which are the first antibodies produced by the immune system when it encounters a new infection. IgM plays a crucial role in the early phase of immune defence.

Unlike IgG, which reflects long-term immunity, IgM rises quickly after exposure to bacteria, viruses, or other pathogens and usually declines as the immune response matures. This makes IgM particularly useful for identifying recent or acute immune activity.

The test is commonly used in immunology, infectious disease assessment, and investigation of immune system disorders.

Why do I need an Immunoglobulin M test?

Abnormal IgM levels may indicate acute infection, immune deficiency, autoimmune disease, or certain blood disorders. Testing helps determine whether the immune system is responding appropriately.

You may need an IgM test if you:

• Have suspected recent or acute infection
• Experience recurrent or unusual infections
• Are being assessed for immune deficiency
• Have unexplained inflammation or fever
• Are undergoing immunoglobulin profiling
• Have liver or autoimmune disease
• Require immune monitoring

Conditions associated with abnormal IgM levels include:

• Acute bacterial or viral infections
• Primary immune deficiencies
• Autoimmune diseases
• Chronic liver disease
• Certain lymphoproliferative disorders

Benefits of the Immunoglobulin M test

• Identifies early immune response
  Indicates recent exposure or infection.
• Supports acute infection assessment
  Useful when symptoms are recent.
• Helps detect immune deficiencies
  Low IgM may impair early immune defence.
• Clinically recognised immune marker
  Used in NHS and specialist diagnostics.
• Supports autoimmune investigations
  Elevated levels may reflect immune activation.
• Complements IgG and IgA testing
  Part of full immunoglobulin profiling.
• Useful in monitoring immune disorders
  Helps track immune function over time.
• Simple blood test
  Requires only a single sample.

Step by step – how the test works

You can access Immunoglobulin M testing UK-wide through two options:

1. Clinic appointment
   Choose your nearest UK clinic, where a healthcare professional will take your blood sample.
2. At-home or hotel visit (£60 extra)
   A qualified phlebotomist comes to your home or hotel, so you don’t need to travel.

Your sample is analysed in an accredited UK laboratory, and results are delivered securely.

Your results explained

Low IgM levels

May indicate immune deficiency or impaired early immune response.

Typical UK reference range:

• < 0.4 g/L

Normal IgM levels

Suggest appropriate early immune function.

Typical UK reference range:

• 0.4–2.3 g/L

High IgM levels

May indicate acute infection, chronic inflammation, or certain immune disorders.

Typical UK interpretation:

• > 2.3 g/L

Reference ranges may vary slightly between laboratories.