Hidden hair disease rarely shows symptoms until infection occurs in the sinus tract. Typically, there are tiny pits in the caudal midline without any sensation. The pits have tiny holes and in some cases are difficult to access with a lacrimal sac probe. So, what tests should be done when a patient presents with a small pit in the midline of the tail without any sensation? Here is a brief introduction: 1. Introduction to blood routine: Blood routine is the most general and basic blood test. Blood consists of two major parts, liquid and tangible cells, and routine blood test is the cellular part of blood. Blood has three different functions of cells – red blood cells (commonly known as red blood cells), white blood cells (commonly known as white blood cells), platelets. Diseases are determined by observing changes in number and morphological distribution. It is one of the common auxiliary tests used by doctors to diagnose the disease. 2.Introduction of blood test: Blood test is the most general and basic blood test. It is a test to determine anemia, cholesterol, diabetes, various infections, kidney function, calcium, liver function, blood disorders and physical abnormalities through blood analysis. It is one of the most common laboratory tests performed in hospitals. Blood tests are ordered by a physician who uses the results to clarify or support a diagnosis, monitor or decide on treatment, and screen for undetermined conditions.