Normal people with colds do not usually have occult blood. Occult blood usually includes occult blood in urine and occult blood in stool. Physiological reasons, medication reasons, and other disease factors are the most commonly considered causes of occult blood. 1. Occult blood in urine (1) After strenuous exercise, heavy physical labor or standing for a long time, a transient trace of red blood cells (i.e., occult blood in urine) may appear in the urine. (2) Drug hematuria, such as taking cold medicines containing diclofenac, may cause damage to renal function, occult blood in the urine, especially for children who use drugs. (3) Occult blood in urine may occur when there is a combination of nephritis, kidney stone, genitourinary tract infection and other diseases during cold and flu. 2. Occult blood in stool: mostly due to gastrointestinal bleeding, considered to be related to inflammation and ulcer. Inflammation may also cause positive occult blood in the stool; in the case of peptic ulcer, positive occult blood in the stool, black stool, and if the amount of bleeding is large, it will also manifest as vomiting blood, vomiting coffee-like material. Normal people with colds usually do not have occult blood, so it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, and then give targeted treatment or therapy.