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Immunoassay for Immunoglobulin M (IgM) Antibody to *Pneumocystis jirovecii* (Pneumocystis carinii in older references)

Published: August 9, 2026Updated: August 16, 2026

This test measures antibodies in your blood that your immune system produces in response to an infection by *Pneumocystis jirovecii*, a fungus that can cause a serious lung infection called pneumocystis pneumonia (PCP).

Quick summary

["Detects past or recent exposure to *Pneumocystis jirovecii* infection."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
105982-3
Short code
IgM kappa Ser Ql IFE
Synonyms
IgM kappa Ser Ql IFE
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
immunofixation
CPT
82784
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What This Test Measures

IgM antibodies are part of your immune system’s response to an infection. If you have been exposed to *Pneumocystis jirovecii* (the fungus responsible for PCP), your body may produce these antibodies. This test checks for their presence in your blood.

Why It’s Done

Doctors may order this test if you have symptoms of PCP, such as persistent cough, shortness of breath, or fever, especially if you have a weakened immune system (e.g., due to HIV/AIDS, chemotherapy, or other conditions). It can also help confirm a diagnosis after other tests.

Who Might Need This Test

People with weakened immune systems, such as those with HIV/AIDS, undergoing chemotherapy, or taking long-term steroids, may need this test to monitor for PCP. It may also be used in high-risk groups (e.g., transplant recipients) for screening or follow-up.

What to Expect Before the Test

No special preparation is usually needed. A blood sample is drawn from a vein in your arm, similar to other blood tests. You may feel a slight pinch, but it typically takes only a few minutes.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

IgM to *Pneumocystis* Antibody

Frequently asked questions

If your test results are positive, it suggests you have had an infection by *Pneumocystis jirovecii* at some point. However, a positive result does not always mean you currently have PCP. Your doctor will consider your symptoms, medical history, and other test results to diagnose the condition.
A positive IgM result may indicate past exposure, but it does not always mean you are actively infected. If you are at high risk for PCP, your doctor may order follow-up tests or treatments to prevent or manage the infection.
What does a positive result mean?
A positive result means your body has detected antibodies to *Pneumocystis jirovecii*, suggesting you were previously exposed to the fungus. However, this does not always mean you are currently infected. Your doctor will evaluate your symptoms and other test results to determine if treatment is needed.
Can this test be used to diagnose PCP right away?
No, this test alone cannot diagnose PCP. It is often used alongside other tests, such as chest X-rays, CT scans, or pulmonary function tests, to confirm an infection. Your doctor will use the test results in combination with clinical findings to make a diagnosis.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy