What this test measures
This is a more sensitive variant of the standard serum IgM assay, optimised to quantify very low concentrations of IgM. The standard IgM assay is calibrated for the normal adult range (~50–300 mg/dL) and reports "low" simply when the value is below the lower limit. The low-concentration assay extends measurement down to the single-digit mg/dL range, so it can distinguish "very low but present" from "essentially absent" — clinically important in selective IgM deficiency, hyper-IgM syndrome (where IgM is normal or high but other immunoglobulins are low), and neonatal congenital infection workups.
IgM is the first immunoglobulin produced after a new infection or vaccination. Its presence in a newborn (since maternal IgM does NOT cross the placenta) is a marker of intrauterine infection. The low-concentration assay is sensitive enough to detect neonatal IgM at very low levels.
Why it matters
Selective IgM deficiency is one of the more common primary humoral immunodeficiencies, often presenting with recurrent respiratory infections, autoimmunity, and atopic disease. The low-concentration assay confirms genuinely low IgM rather than a borderline-normal value at the assay's lower limit.
In neonates and infants the test is used for: detecting intrauterine infection (TORCH agents — toxoplasma, rubella, CMV, herpes — all raise neonatal IgM); evaluating recurrent infections from early infancy; and as part of a suspected primary immunodeficiency workup (X-linked agammaglobulinaemia, common variable immunodeficiency, hyper-IgM syndrome).
How to prepare
No fasting required. Disclose any recent infection (raises IgM transiently), recent vaccination (raises IgM), and any immunosuppressive therapy. In neonates, the test is often part of a TORCH screen — bring the antenatal and birth notes so the lab can interpret correctly.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| IgM (Low-Concentration Assay) (mg/dL)[1][2][3] | Adult 50 – 300 · Neonate < 20 (low-conc assay required for accurate reporting) | < 50 mg/dL (adult) or < 20 mg/dL on the low-concentration assay: selective IgM deficiency, hyper-IgM syndrome (with normal/high IgM but low IgG/IgA), common variable immunodeficiency (CVID), X-linked agammaglobulinaemia, severe protein-losing states, immunosuppression. | Elevated IgM at any age: acute infection, hyper-IgM syndrome (paradoxically high IgM with low IgG/IgA), Waldenström macroglobulinaemia (very high), chronic infection (malaria, kala-azar), autoimmune disease, primary biliary cholangitis. In neonates, any detectable IgM suggests intrauterine infection. |
When the low-concentration IgM assay matters
| Clinical setting | Why low-conc assay |
|---|---|
| Suspected selective IgM deficiency | Distinguish "very low" from "borderline normal" |
| Hyper-IgM syndrome workup | Quantify IgG and IgA accurately when IgM is normal/high |
| Neonatal TORCH screen | Detect very low neonatal IgM that signals intrauterine infection |
| Recurrent infections in infants | Evaluate primary immunodeficiency |
Frequently asked questions
What does "low concentration" mean in this test name?
It refers to the assay's ability to accurately measure very low IgM levels — well below the normal adult range. The standard IgM assay just reports "below detection limit"; the low-concentration assay gives an actual number.
When is this test ordered?
Workup of suspected primary immunodeficiency (selective IgM deficiency, hyper-IgM syndrome, CVID), recurrent infections in infants, neonatal TORCH screening, and any situation where knowing exactly how low IgM is matters.
Why is neonatal IgM important?
IgM does NOT cross the placenta from mother to baby. Any IgM in a newborn's blood is made by the baby — usually as a response to an intrauterine infection (toxoplasma, rubella, CMV, herpes, syphilis). The low-concentration assay catches very low levels that might otherwise be missed.
What is hyper-IgM syndrome?
A primary immunodeficiency where the immune system cannot "switch" from making IgM to making IgG or IgA. IgM is normal or high, but IgG, IgA, and IgE are very low — leading to recurrent infections, especially opportunistic ones.
How is selective IgM deficiency treated?
There is no specific replacement therapy for IgM. Management focuses on prompt treatment of infections, prophylactic antibiotics in some cases, and treating any associated autoimmune or atopic disease.
Should I be tested if I have recurrent sinusitis?
Recurrent sinusitis, pneumonia, or ear infections in adults can be a sign of immunoglobulin deficiency. Standard IgG, IgA, and IgM tests are usually the first step; the low-concentration assay is used when standard tests show borderline or very low values.
Related Immunology tests
Tests commonly ordered alongside IGM LOW CONCENTRATION, or that help interpret an unexpected result.
Sources & references
- NIH MedlinePlus — Immunoglobulin Test · accessed 2026-05-30T00:00:00.000Z
- NCBI StatPearls — Immunoglobulin M · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Labs — IgM · accessed 2026-05-30T00:00:00.000Z
- AAAAI — Primary Immunodeficiency · accessed 2026-05-30T00:00:00.000Z
Book with Zelnoo
Get your IGM LOW CONCENTRATION test done at home — transparent prices, NABL-accredited labs.
Zelnoo lets you compare diagnostic test prices across NABL-accredited labs in Mumbai & Thane, book a free home phlebotomist visit, and receive digital reports in 24–48 hours into a consent-first report vault. No subscriptions, no membership fees — pay only for the test you book.
Book IGM LOW CONCENTRATION now