Diabetes mellitus is a chronic condition in which blood glucose stays too high because the body does not make enough insulin or cannot use insulin well. This cheat sheet helps students connect the science of glucose regulation with practical management steps used in health care. It is useful for understanding diagnosis, monitoring, medicines, lifestyle choices, and safety concerns.
It is for education only and does not replace medical advice from a licensed clinician.
The core ideas include how insulin and glucagon regulate blood sugar, how Type 1 and Type 2 diabetes differ, and how blood glucose is measured. Important values include fasting plasma glucose, oral glucose tolerance, random plasma glucose with symptoms, and A1C. Management focuses on balanced nutrition, physical activity, glucose monitoring, medication use, and preventing complications.
Students should also know how to recognize and respond to hypoglycemia and hyperglycemia.
Key Facts
- Diabetes mellitus is diagnosed when fasting plasma glucose is 126 mg/dL or higher on repeat testing, A1C is 6.5% or higher, or 2-hour oral glucose tolerance test glucose is 200 mg/dL or higher.
- Prediabetes is commonly defined as fasting plasma glucose 100 to 125 mg/dL, A1C 5.7% to 6.4%, or 2-hour oral glucose tolerance test glucose 140 to 199 mg/dL.
- Type 1 diabetes is usually caused by autoimmune destruction of pancreatic beta cells, leading to little or no insulin production.
- Type 2 diabetes involves insulin resistance and often a gradual decline in insulin production by pancreatic beta cells.
- A common nonpregnant adult A1C goal is less than 7%, but individual targets may vary based on age, health status, and risk of low blood sugar.
- Hypoglycemia is often defined as blood glucose below 70 mg/dL and is commonly treated with 15 g of fast-acting carbohydrate, followed by rechecking glucose in 15 minutes.
- Insulin lowers blood glucose by helping cells take up glucose and by reducing glucose release from the liver.
- Long-term high blood glucose can damage blood vessels and nerves, increasing the risk of retinopathy, kidney disease, neuropathy, heart disease, and poor wound healing.
Vocabulary
- Blood glucose
- Blood glucose is the amount of sugar circulating in the blood, usually measured in mg/dL.
- Insulin
- Insulin is a hormone made by pancreatic beta cells that helps glucose move from the blood into body cells.
- A1C
- A1C is a blood test that estimates average blood glucose over about the past 2 to 3 months.
- Hypoglycemia
- Hypoglycemia is low blood glucose, often below 70 mg/dL, which can cause shakiness, sweating, confusion, or weakness.
- Hyperglycemia
- Hyperglycemia is high blood glucose, which may cause thirst, frequent urination, fatigue, and blurred vision.
- Insulin resistance
- Insulin resistance means body cells do not respond well to insulin, so glucose remains higher in the blood.
Common Mistakes to Avoid
- Confusing Type 1 diabetes with Type 2 diabetes is wrong because Type 1 mainly involves insulin deficiency, while Type 2 mainly begins with insulin resistance.
- Using A1C as a moment-by-moment glucose value is wrong because A1C reflects an average over weeks to months, not the current blood glucose level.
- Treating hypoglycemia with only protein or fat is wrong because foods like cheese or nuts do not raise blood glucose quickly enough during a low.
- Skipping glucose monitoring when symptoms occur is wrong because shakiness, fatigue, thirst, or confusion can have different causes and should be checked with a meter or sensor when available.
- Assuming diabetes management is only about avoiding sugar is wrong because carbohydrate amount, medication timing, activity, stress, illness, and sleep can all affect blood glucose.
Practice Questions
- 1 A student has a fasting plasma glucose of 132 mg/dL on two separate days. Based on common diagnostic thresholds, what category does this result suggest?
- 2 A person has blood glucose of 62 mg/dL and is awake and able to swallow. What immediate treatment step is commonly recommended, and when should glucose be rechecked?
- 3 If a patient’s A1C is 8.2% and a common goal is less than 7%, is the value above or below goal, and what does that suggest about average glucose control?
- 4 Explain why physical activity can help many people with Type 2 diabetes improve blood glucose control, even if they do not lose weight.
Understanding Diabetes Mellitus Management Reference
Blood glucose is not a fixed number throughout the day. It changes after meals, during exercise, with stress, and during illness. A1C gives a longer view because glucose slowly attaches to hemoglobin inside red blood cells.
Since red blood cells usually circulate for about three months, the result reflects an average over that period, with recent weeks having more influence. An average can hide important highs and lows.
Two people can have a similar A1C while one has fairly steady readings and the other swings between very low and very high values. Conditions that change red blood cell lifespan, such as anemia, blood loss, or some kidney diseases, can make A1C less reliable.
Glucose meters show a reading at one moment. Continuous glucose monitors use a small sensor under the skin to estimate glucose in fluid between cells. Their main advantage is the pattern over time.
A rising arrow after a meal suggests glucose is still increasing. A falling arrow before exercise may warn of a possible low. Insulin plans often separate background insulin from meal insulin.
Background insulin limits glucose released by the liver between meals and overnight. Meal insulin covers carbohydrate eaten at a meal and may correct a high reading.
Timing matters because different insulin types begin working, peak, and last for different lengths of time. Repeated injections in the same small area can create lumps under the skin, which can make insulin absorption unpredictable.
Food affects glucose most directly through carbohydrate, but the whole meal matters. Fiber, protein, and fat can slow digestion, so glucose may rise later than expected. Physical activity helps muscles take in glucose with less insulin.
This effect can continue after activity ends. Exercise can lower glucose too much when insulin or certain medicines are active, especially if a meal was missed. Illness can raise glucose because stress hormones signal the liver to release stored glucose.
People who use insulin may need to check ketones when glucose is high during illness. Ketones are acids made when the body uses fat heavily for fuel. High ketones with vomiting, deep breathing, or severe tiredness need urgent medical care.
Preventing complications depends on many small habits over years. Blood pressure, cholesterol, sleep, smoking status, and regular movement affect blood vessel health along with glucose levels. Eye examinations can find early retinal damage before vision changes are noticed.
Urine and blood tests can detect kidney stress early. Foot checks matter because nerve damage may reduce pain sensation, allowing a blister or cut to worsen unnoticed.
Students should learn to read glucose data as evidence rather than as a grade. A number can guide the next safe action, such as eating fast carbohydrate for a low, following a personal treatment plan for a high, or asking a health professional for help when patterns keep repeating.