Cetirizine level analysis in the blood is a laboratory test used to measure the concentration of cetirizine, an antihistamine commonly used to treat allergy symptoms such as sneezing, runny nose, and itching caused by allergies or allergic rhinitis. This test can help evaluate treatment effectiveness or monitor drug levels in the blood, especially in patients with kidney problems or those receiving high or long-term doses. It is also used to determine whether there is unwanted accumulation of cetirizine that may affect the body.