A nosocomial infection is one that is acquired in a hospital. This subject is extremely important but cannot be covered in detail in a book that concentrates on laboratory tests. The most common cause of nosocomial infection is the indwelling urinary catheter. Some other important factors are surgery, long-term indwelling vascular catheters or equipment, conditions that depress patient resistance to infection, malnutrition, severe trauma or burns, overuse of antibiotics, and instrumentation of the urinary tract or other areas.