Polymorphonuclear leukocytes (PMNs) are a type of white blood cell that includes neutrophils, eosinophils, basophils, and mast cells. PMNs play a central role in the innate immune system and protect the body against infectious organisms. A high polymorph count in the blood, also known as neutrophilia, is most commonly caused by infections, but can also be elevated in inflammation caused by medical conditions and your bodys reaction to stress. Some of the most common reasons for leukocytes in urine, and other symptoms you might see with them, include urinary tract infections (UTIs) . Therefore, a high polymorph count in the blood is often a sign of an infection in the body. Treatment depends on the underlying cause.