Allergy - Lidocaine (Lignocaine) Anaesthesia Test

Lidocaine (Lignocaine), introduced in 1946, represents the most common local anesthetic (LA) agent employed in local or regional anesthesia. LA is commonly used in dentistry, ophthalmology, minor surgery, and obstetrics. Most allergic reactions are due to cross-reactivity among metabolic product of the ester local anesthetic and para-aminobenzoic acid. True allergy to LA is very rare, with only 1% of all genuine immunological reaction against this medicine. Skin testing is considered to be a useful tool in case of suspected hypersensitivity to local anesthetics. The tests include patch tests, intradermal tests for delayed hypersensitivity, intradermal tests for immediate reactions and skin prick test.

As there are couple of tests available that can diagnose allergy to LA, a patient needs to be prepared according to the testing doctor has ordered. For a patch test or skin prick test, you may have to be prepared to experience some uncomfortable feeling on the skin if you test positive. No other special preparations required for these tests. Inform the doctor beforehand of any medications you are taking or of any other allergic reactions that you may have. Immediate anaphylactic reactions can occur, mediated by IgE antibodies. Signs and symptoms may occur within 10 minutes.

The intradermal test is an easy method and has often been used for identifying reactions to local anesthetics for patients with histories of adverse reactions. Patients with reactions ranging from minor cutaneous manifestations to severe anaphylaxis should be recommended for skin testing before adhering to local anesthesia. Some symptoms can be mistaken for hypersensitivity or allergy & the patient is unnecessarily told they are allergic to local anesthesia. This can lead to problems for dentists with these patients. These quick tests help doctors to determine whether the LA contain epinephrine for patients allergic or reactive to it.

A test is performed based on a doctor's prescription. An intradermal test is performed using local anesthetics, including lidocaine hydrochloride. It involves injecting local anesthetics on the extensor surface of the arm in a small volume (0.02 ml) The reaction produces a wheel of few mm in diameter. As a negative control, saline is injected to the patient. Redness or swelling in the area can be seen around the injection site. It is measured every 5 minutes for 20 minutes, to obtain the desired results. In a challenge test, a local anesthetic is injected into the oral mucosa in small dosage from 0.1 to 1.0 ml. Findings and vital signs are observed for 30 min.