Allergy Notes: What is Chronic Urticaria Index?

Patented test, not FDA-approved

"Chronic Urticaria Index" (TM) is a trademarked term and test which consists of basophil histamine release assay. If the test is positive (index greater than 10), the patient may have chronic autoimmune urticaria.

Literature review

The test is nonspecific - it measures only histamine release from the patient's cells and compares it to a normal control. It does not measure antibodies or autoantibodies. Anti-FcεRI may be more specific in patients with chronic autoimmune urticaria. As of December 2, 2009, there are no published studies of the "Chronic Urticaria Index" in medical literature or book references although the general method itself has been described in several journal article.

CU Index (Chronic Urticaria Index) is available from a few reference laboratories (ARUP is one of them). Patients with a chronic form of urticaria with a positive functional anti-FcεR test result likely have an autoimmune basis for their disease. A positive result does not indicate which autoantibody (anti-IgE, anti-FcεRI, or anti-FcεRII) is present. This test is usually combined with thyroid function, antithyroid microsomal titers, and peroxidase antibody titers.

How is the test done?

The result is reported as an index value. The reference range for a healthy non-CU population is less than 10. Values greater than or equal to 10 indicate that donor basophils were stimulated by patient serum to release histamine. The larger the value the more histamine released.

Method:

1. Ex-Vivo challenge and cell culture. Donor blood cells are incubated with patient serum, a negative control and a positive control. Following the ex-vivo challenge, the cells are centrifuged and the supernatant is recovered for assay of histamine released.

2. Histamine analysis. Using a quantitative enzyme immunoassay, the histamine released into the supernatant is measured and compared to the total histamine in the basophils.

The has not been approved or cleared by the FDA.

According to one of the laboratories, "patients with a chronic form of urticaria who are positive with the CU Index (Functional Anti-FcεR test) have an autoimmune basis for their disease. A positive result does not indicate which autoantibody (anti-IgE, anti-FcεRI or anti-FcεRII) is present."

The name "Functional Anti-FcεR test" is a misnomer because the test is really a basophil histamine release assay rather than an assessment of the function of any specific antibody.

Recommendations

Until new evidence becomes available, it is probably better to use anti-FcεRI for assessment of patients with suspected chronic autoimmune urticaria rather than the Chronic Urticaria Index (TM).