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Diagnosing hereditary angioedema
Diagnosing HAE is not difficult in principle, however patients frequently get a wrong diagnosis primarily because of its rarity, with many doctors not coming across a single patient with this condition in their entire career. In addition, HAE ’s non-specific symptoms, which often resemble those of more common diseases such as allergy, hives (urticaria), intestinal colic or appendicitis, can lead physicians to a wrong conclusion easily. As a result, it can take a relatively long time for it to be diagnosed correctly. Whilst the disease remains undetected, the patient is at risk of suffocation due to acute swelling in the larynx or, in the case of intestinal oedema, of undergoing unnecessary laparoscopy or even having their appendix removed.
Diagnosis
Most cases of angioedema are due to an allergic reaction. Thus HAE diagnosis, caused by C1-inhibitor deficiency, requires laboratory analysis of blood samples or genetic testing in order to establish the diagnosis.
There are two specific blood tests that confirm HAE:
1. C1-inhibitor quantitative (antigenic)
2. C1-inhibitor functional
Traditionally, HAE has been classified into two types. The most common form of the disease -Type I- is characterised by low quantitative levels of C1-inhibitor and affects about 85% of patients. Type II HAE affects the other 15% and is characterised by normal or elevated levels of C1-inhibitor that has abnormal function. A scientific article in the September 2000 volume of the British medical journal Lancet suggests there is another form of HAE that only affects females, but is not caused by C1-inhibitor deficiency. It has been proposed that this disease should be labeled as HAE Type III.
Diagnosis is difficult in patients who only have episodes of swelling in the intestine. Initially, further information is obtained by establishing whether anyone else in the patient’s family has had the disease (known as family history). However, only a laboratory analysis can provide final confirmation.
Laboratory analysis is based on detection of complement factor C4 in the blood, which is used during activation of the complement cascade. More C4 is used in patients with untreated HAE leaving them with lower blood levels of C4 than in healthy people. Detecting reduced C4 levels is now regarded as a completely reliable way of predicting a C1-INH deficiency, which is then confirmed by a follow-up measurement of quantitative and functional C1-INH levels.
Diagnosis
Most cases of angioedema are due to an allergic reaction. Thus HAE diagnosis, caused by C1-inhibitor deficiency, requires laboratory analysis of blood samples or genetic testing in order to establish the diagnosis.
There are two specific blood tests that confirm HAE:
1. C1-inhibitor quantitative (antigenic)
2. C1-inhibitor functional
Traditionally, HAE has been classified into two types. The most common form of the disease -Type I- is characterised by low quantitative levels of C1-inhibitor and affects about 85% of patients. Type II HAE affects the other 15% and is characterised by normal or elevated levels of C1-inhibitor that has abnormal function. A scientific article in the September 2000 volume of the British medical journal Lancet suggests there is another form of HAE that only affects females, but is not caused by C1-inhibitor deficiency. It has been proposed that this disease should be labeled as HAE Type III.
Diagnosis is difficult in patients who only have episodes of swelling in the intestine. Initially, further information is obtained by establishing whether anyone else in the patient’s family has had the disease (known as family history). However, only a laboratory analysis can provide final confirmation.
Laboratory analysis is based on detection of complement factor C4 in the blood, which is used during activation of the complement cascade. More C4 is used in patients with untreated HAE leaving them with lower blood levels of C4 than in healthy people. Detecting reduced C4 levels is now regarded as a completely reliable way of predicting a C1-INH deficiency, which is then confirmed by a follow-up measurement of quantitative and functional C1-INH levels.
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Author: Jerini AG |
