Endocrinology is the branch of medicine focused on hormones and the glands that produce them. It covers the diagnosis and treatment of conditions that arise when hormone levels are too high, too low, or when the glands themselves develop problems like nodules or tumors. If you’ve ever had your thyroid checked, your blood sugar monitored for diabetes, or been told your calcium levels were off, you’ve already brushed up against endocrinology.
The Endocrine System at a Glance
Your endocrine system is a network of glands spread throughout your body, each releasing hormones directly into your bloodstream. These glands include the hypothalamus, pituitary gland, pineal gland, thyroid, parathyroid glands, thymus, adrenal glands, and pancreas. The testes in males and the ovaries in females are also part of the system, as is the placenta during pregnancy.
Each gland has a specific job. Your thyroid regulates metabolism and energy. Your adrenal glands, which sit on top of your kidneys, manage stress responses, blood pressure, and inflammation. Your pancreas controls blood sugar by releasing insulin. The pituitary gland, a pea-sized structure at the base of your brain, is sometimes called the “master gland” because it sends signals that tell many of the other glands when to ramp up or dial back their hormone production.
How Hormones Work
Hormones are chemical messengers. They travel through the bloodstream until they reach a cell that has the right receptor for them, like a key fitting into a specific lock. Each receptor binds its hormone tightly and with high specificity, which is why a hormone released by your thyroid doesn’t accidentally trigger a response in your bones.
A few things make this system elegant. First, it’s saturable: your cells have a limited number of receptors, so there’s a natural ceiling on how much any one hormone can stimulate a cell. Second, it’s reversible. A hormone binds, delivers its message, then detaches without being permanently changed. This allows the system to respond dynamically, turning signals on and off as conditions in your body shift throughout the day.
Conditions Endocrinologists Treat
The range of endocrine disorders is broad. A Johns Hopkins review found that endocrine conditions affecting at least 5% of U.S. adults include diabetes, impaired blood sugar regulation, obesity, metabolic syndrome, osteoporosis, low vitamin D, erectile dysfunction, abnormal cholesterol levels, and thyroid inflammation. Less common conditions, affecting under 1% of the population, include pituitary tumors and childhood diabetes.
Some of the most frequently seen conditions include:
- Diabetes (Type 1 and Type 2): The pancreas either stops producing insulin or the body stops responding to it properly, causing blood sugar to rise.
- Thyroid disorders: An underactive thyroid (hypothyroidism) slows your metabolism, causing fatigue, weight gain, and cold sensitivity. An overactive thyroid (hyperthyroidism) speeds everything up, leading to weight loss, anxiety, and a rapid heartbeat. A normal TSH level falls between 0.4 and 4 mIU/L.
- Adrenal disorders: Cushing’s syndrome occurs when your body produces too much cortisol over a long period. Addison’s disease is the opposite, where your adrenal glands don’t produce enough.
- Osteoporosis: Hormonal changes, especially after menopause, can accelerate bone loss.
- Polycystic ovary syndrome (PCOS): A hormonal imbalance in women that can affect periods, fertility, and metabolism.
- Growth disorders: In children, too much or too little growth hormone can cause abnormal growth patterns.
How Endocrine Conditions Are Diagnosed
Diagnosis usually starts with blood tests measuring specific hormone levels. But a single blood draw doesn’t always tell the full story, because hormone levels fluctuate throughout the day. That’s where specialized tests come in. Endocrinologists use two main types: stimulation tests and suppression tests.
A stimulation test checks whether a gland can respond when it’s supposed to. For example, if a doctor suspects your adrenal glands aren’t producing enough cortisol, they’ll inject a synthetic version of the hormone that normally tells your adrenals to work. Then they measure whether your cortisol rises appropriately within 30 minutes. If it doesn’t, that confirms the gland is underperforming.
A suppression test works in the opposite direction. It checks whether a gland will quiet down when given a signal to stop. To screen for Cushing’s syndrome, for instance, you take a small pill at bedtime that should tell your brain to stop signaling cortisol production. A blood sample the next morning reveals whether your cortisol dropped as expected. If it stays high, that suggests your body is overproducing cortisol on its own, independent of normal feedback signals.
These tests are paired with imaging when needed. Ultrasounds can evaluate thyroid nodules, and MRI scans can look for pituitary tumors.
What an Endocrinologist Does
An endocrinologist is an internal medicine doctor who has completed an additional two years of fellowship training specifically in endocrinology, diabetes, and metabolism. That means at least 10 years of education and training after college: four years of medical school, three years of internal medicine residency, and two years of subspecialty fellowship. They’re certified by the American Board of Internal Medicine.
Most people see an endocrinologist through a referral from their primary care doctor. Common reasons for referral include a thyroid nodule or goiter, blood sugar levels that suggest diabetes (a fasting glucose above 126 mg/dL or an A1c above 6.5%), unexplained weight changes, abnormal growth in children, or symptoms that don’t respond to initial treatment. You might also be referred if lab results show hormone levels that your primary care doctor isn’t comfortable managing, such as a significantly elevated TSH or very high cholesterol that hasn’t responded to lifestyle changes after six months.
At your first visit, expect a thorough review of your symptoms, family history, and previous lab work. The endocrinologist will likely order additional blood tests and possibly imaging. Many endocrine conditions are managed with ongoing monitoring and medication adjustments rather than surgery, so follow-up visits are common.
Pediatric vs. Adult Endocrinology
Children aren’t just small adults, and their hormonal issues look very different from those of grown-ups. Pediatric endocrinologists focus on conditions tied to growth and development: short stature, early or delayed puberty, congenital thyroid problems detected at birth, and Type 1 diabetes, which most often appears in childhood. A child whose height falls below the 3rd percentile for their age, or who is crossing growth percentiles on repeated measurements, is a typical candidate for a pediatric endocrinology evaluation.
Adult endocrinologists, by contrast, spend more of their time managing Type 2 diabetes, thyroid disease, osteoporosis, and reproductive hormone issues. The overlap exists, but the training and clinical focus are distinct enough that the two are treated as separate subspecialties.