Developments in Brief : New Test Diagnoses True Allergic Reactions

A new test appears to offer the first practical way of determining whether a person has experienced a severe allergic reaction, thus avoiding the possibility of confusion with other ailments.

“Currently there’s no test or method to tell you whether a particular reaction was allergic or not,” said Dr. Lawrence B. Schwartz, who helped develop the test at the Medical College of Virginia in Richmond.

Doctors now diagnose severe allergic reactions based on a patient’s symptoms, which can often be confused with other medical problems such as heart attacks. In severe allergic reactions, victims’ blood pressure drops dangerously low and can cause damage to the heart and brain and sometimes death.

In a study published in the current issue of the New England Journal of Medicine, Schwartz and colleagues say that elevated levels of an enzyme known as tryptase appear to indicate that a person has experienced a severe allergic reaction.

Tryptase is an enzyme released by immune system cells known as mast cells, which become activated in an allergic reaction. Mast cells also release a substance known as histamine, which is responsible for many allergic symptoms. But histamine only remains in the system for several minutes. Tryptase is more practical because it remains elevated for hours, Schwartz said.

The researchers compared tryptase levels in 54 people--those who had experienced severe allergic reactions, those who had heart problems, those who had infections, those who had a condition known as mastocytosis in which they had increased numbers of mast cells and people who were healthy.

Only the six patients who had severe allergic reactions and 17 patients with mastocytosis had elevated tryptase levels, Schwartz said.

“When positive levels of this enzyme are found in the blood, it clearly indicates allergic reaction of some sort,” he said.

The test should allow doctors to give prompt treatment and avoid treating the patient for something else, Schwartz said.

The allergic reactions experienced by patients in the study were caused by a variety of things, including antibiotics, food and insect bites. One patient who had an allergic reaction to honeydew melon was initially thought to have suffered a heart attack.