What Are the Subspecialties of Internal Medicine? The Full Map, from Cardiology to Rheumatology

One specialty, many branches

Internal medicine is the specialty of adult health, and it works like a trunk with branches. Every internist completes the same core residency in internal medicine — the pathway described in the ACGME's internal medicine overview. Some then stop there and practice as general internists. Others continue into fellowship training in a narrower field and become subspecialists. The American Board of Internal Medicine certifies physicians first in internal medicine itself, and then, for those who pursue it, in the subspecialties layered on top.

That structure explains something that confuses a lot of patients: your cardiologist and your general internist trained in the same specialty first. The cardiologist simply kept going. (Whether the general internist counts as a "specialist" at all is a separate question — see is an internal medicine doctor considered a specialist.)

The major subspecialties and what each covers

Here are the branches you are most likely to be referred to, described by organ system or problem area:

• Cardiovascular disease (cardiology) — the heart and blood vessels: rhythm problems, heart failure, coronary artery disease. The NHLBI's health topics library is the NIH's plain-language reference for this territory.
• Gastroenterology — the digestive tract, liver, and pancreas; also the subspecialty that performs colonoscopies and endoscopies.
• Endocrinology — hormones and metabolism: diabetes, thyroid disease, and related conditions. The NIDDK's health information pages cover much of this ground for patients.
• Nephrology — the kidneys: chronic kidney disease, dialysis, and related blood pressure and electrolyte problems.
• Pulmonary disease — the lungs: asthma, COPD, and other breathing disorders, often combined with critical care medicine.
• Hematology — blood disorders: anemias, clotting problems, and blood cancers.
• Medical oncology — cancer treated with medication; frequently paired with hematology in a single practice.
• Infectious disease — complex or persistent infections and antibiotic management.
• Rheumatology — autoimmune and joint conditions such as rheumatoid arthritis and lupus.
• Geriatric medicine — the health of older adults, with attention to multiple coexisting conditions and medications.

There are additional fields — critical care medicine, allergy and immunology, sleep medicine, hospice and palliative medicine, and others — but the list above accounts for most referrals a general internist makes. The American College of Physicians' description of internal medicine situates all of these within the larger specialty.

How the trunk and branches work together

In practice, the system runs on referrals. A general internist — or a family doctor, whose training covers a different range — handles the broad picture: checkups, common chronic conditions, and sorting out new symptoms. When a problem needs deeper expertise or a procedure, the internist refers you to the matching subspecialist, and the subspecialist reports findings back.

A few practical points about navigating that chain:

• Referrals usually flow through the generalist. Many insurance plans want a primary care referral before a subspecialist visit, and starting with the generalist means someone keeps the whole picture in view.
• The subspecialty name tells you the organ system, not your diagnosis. Being referred to a nephrologist means a kidney-related question needs expert eyes, nothing more specific than that.
• One person, several branches. Some physicians hold more than one certification — pulmonary and critical care is a common pairing — so a doctor's profile may list two or three fields.

What this list is not

This page is a map of how internal medicine is organized, not guidance on which doctor to see for a given symptom. Which subspecialist, if any, fits your situation is a judgment call your own physician makes with your history in hand — a good thing to ask about directly at a visit.