What test is required to elicit cold urticaria in patients with PLAID and FCAS?

The evaporative cooling test is the correct choice for eliciting cold urticaria in patients with PLAID (PLAutoimmune lymphoproliferative syndrome with Isolated Defects) and FCAS (Famillial Cold Autoinflammatory Syndrome). This test is specifically designed to provoke a reaction in individuals who have a hypersensitivity to cold temperatures.

During the evaporative cooling test, a patient's skin is exposed to a controlled cooling environment, which simulates the conditions that trigger urticaria in sensitive individuals. The process involves allowing the skin temperature to drop by applying a wet cloth or using an evaporative cooling method, which leads to rapid cooling. In susceptible patients, this can result in urticaria-like reactions, such as wheals or hives.

This method is particularly effective in evaluating cold urticaria because it closely replicates the conditions under which the symptoms would typically occur, providing a reliable assessment of the patient's condition related to cold exposure. Understanding how to utilize this test is crucial in managing and diagnosing patients with cold-induced illnesses like PLAID and FCAS.