Dried blood spot C1-INH testing may aid HAE diagnosis: Study
Assay appears to work as well as standard test
HAE attacks
An assay that measures C1 inhibitor (C1-INH) activity on a dried blood spot after a blood sample is blotted onto a piece of filter paper appears to work as well as a standard, color-based assay to diagnose hereditary angioedema (HAE) and is easier to handle, a study found.
Dried blood spot testing “may allow more accessible hereditary angioedema diagnostic testing, especially in underserved regions,” the researchers wrote.
The study, “Clinical validity of dried blood spot assay for the measurement of functional C1 inhibitor in hereditary angioedema,” was published in the Journal of Allergy and Clinical Immunology: Global.
The most common types of HAE are caused by mutations in the gene that provides instructions for making C1-INH. Normally, C1-INH regulates the production of bradykinin, a signaling molecule that causes blood vessels to become more permeable. When C1-INH is missing or is faulty, too much bradykinin is produced, causing fluid to leak out of blood vessels and pool into nearby tissues, causing swelling.
Measuring C1-INH activity is essential to establish a diagnosis of HAE.
Easier test can be used in remote locations
Enzyme-linked immunosorbent assay (ELISA) or chromogenic (color-based) assays are the two types of standard diagnostic tests that are normally used to measure C1-INH activity. However, these assays require fresh blood samples and specialized facilities, which can make them difficult to use in remote or underserved areas.
“On the basis of the clinical presentation, patients with HAE may be misdiagnosed with other types of angioedema (allergic or nonallergic),” the researchers wrote. “In patients with HAE, receiving a correct diagnosis is essential to support appropriate management of the disease and avoid ineffective treatments … and/or unnecessary interventions.”
In an effort to make testing easier, researchers developed a dried blood spot assay that uses a small amount of blood dried on blotting paper. This method allows samples to be stored and transported for later testing, making it more practical for use in remote locations where immediate laboratory access may be limited.
To find out if the assay would work as well as existing ones, researchers compared it with ELISA and chromogenic assays in a group of 30 HAE patients and 100 healthy individuals.
After allowing blood to dry for at least three hours, researchers measured how well C1-INH stopped the activity of a protein called C1s protease. They then checked the assay’s sensitivity (how well it identifies patients with HAE) and specificity (how well it rules out HAE in healthy individuals).
The dried blood spot assay had high sensitivity (93%) and specificity (97%). In a smaller subset of 29 HAE patients and 50 healthy individuals, both the dried blood spot and chromogenic assays had high sensitivity (100% vs. 97%) and specificity (94% vs. 100%). ELISA had lower sensitivity (62%), but similar specificity (100%).
The findings suggest the DBS assay performs similarly to the chromogenic assay, and the ease of sample collection makes it particularly valuable for expanding diagnostic access to remote or underserved areas, the researchers said.
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