Q. What is the most common blood type?

The approximate distribution of blood types in the United States population is as follows. Distribution may be different for specific racial and ethnic groups: O-positive: 38 percent; O-negative: 7 percent; A-positive: 34 percent; A-negative: 6 percent; B-positive: 9 percent; B-negative: 2 percent; AB-positive: 3 percent, and AB-negative: 1 percent. Type O-negative blood is called the universal donor type because it is compatible with any blood type. Type AB-positive blood is called the universal recipient type because a person who has it can receive blood of any type. People over the age of 69 require half of all whole blood and red blood cells transfused, according to the National Blood Data Resource Center (NBDRC). With an aging population and advances in medical treatments requiring blood transfusions, the demand for blood is increasing. On any given day, an average of 38,000 units of red blood cells are needed.

Q. What exactly is GERD and how can I tell if I have it? I get lots of heartburn. Heartburn two or more times weekly may be caused by Gastroesophageal Reflux Disease (GERD). See a doctor if you have heartburn too often. The doctor can test for GERD. In the upper GI series, you swallow a liquid barium mixture. Then a radiologist watches the barium as it travels down your esophagus and into the stomach. Another test is an endoscopy, in which a small lighted flexible tube is inserted into the esophagus and stomach. GERD makes stomach acid flow up into your esophagus. There is a valve at the lower end of the esophagus that is designed to keep acid in the stomach. In GERD, the valve relaxes too frequently, which allows acid to reflux, or flow backward. A hiatal hernia may contribute to GERD. A hiatal hernia occurs when the upper part of the stomach is above the diaphragm, which is the muscle wall separating the stomach from the chest. The diaphragm helps the valve keep acid from coming up into the esophagus. When GERD is not treated, you can suffer from severe chest pain, narrowing or obstruction of the esophagus, bleeding, or a pre-malignant change in the lining of the esophagus. One study showed that patients with chronic, untreated heartburn were at substantially greater risk of developing esophageal cancer.

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