Subspecialty internal medicine in the United States: in and outside the hospital.

In the U.S. the subspecialties of internal medicine are well integrated in the overall discipline of internal medicine and each one is also unique. The American Board of Internal Medicine at present certifies 16 unique subdisciplines, which are, in order from the largest to the smallest: cardiology (14,000 certified cardiologists), gastroenterology (10,000 certified), pulmonary disease (9000 certified), critical care medicine (6500 certified), hematology, oncology, nephrology, infectious diseases, allergy and immunology, endocrinology, rheumatology, geriatrics, sport medicine, adolescent medicine. General internal medicine is the first level of certification after three years of training: the above-mentioned subspecialties are the second level (after an additional 2 to 3 years of training). Some subspecialties are at a third level or "third tier". Within cardiology, "third tier" certification recognizes clinical cardiac electrophysiology and interventional cardiology. These disciplines require an additional, fourth year of cardiac training and prior certification in cardiology. Between the departments of internal medicine and the subspecialty divisions there is often a "healthy tension" stemming from unavoidable inequities in the financial contributions of the subspecialties to the department. Currently, there is a decline in specialization rate due to a variety of converging factors, among them restricted direct access to specialists in HMOs, and the developing hospitalist movement: full-time hospitalists are less likely to need subspecialist consultation than other generalists.