Appendicitis is also frequently misdiagnosed in the elderly because, even when the appendix is badly inflamed, pain is typically modest and patients do not have a temperature. In 40 to 75 percent of people over the age of 60, the appendix has ruptured by the time it is medically removed. Approximately 80,000 Americans per year require surgery for appendicitis; half are under the age of 18. In children, the appendix serves as a storage tank for toxins produced by bacteria within the gut. Appendicitis occurs when these toxins trigger an inflammatory response that causes severe abdominal pain and increases blood clotting factors which may lead to infection if the appendix becomes ruptured. In adults, acute appendicitis is most commonly caused by obstruction of the appendiceal lumen from fecaliths or mucus buildup. Other causes include inflammation due to bacterial infections, tumors, or autoimmune diseases. The incidence of appendicitis increases with age; approximately 90% of cases occur in individuals younger than 50 years old. In very old people (over 70 years old), acute appendicitis is less common but still occurs in about 10% of cases. In general, acute appendicitis is diagnosed based on patient history and physical examination findings. Laboratory tests are usually not necessary to make the diagnosis. Ultrasound may be used to confirm the diagnosis before appending a tube into the abdomen to remove the appendix.