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Understanding Diabetes Insipidus vs. Diabetes Mellitus

What is Diabetes Insipidus?

Diabetes insipidus is a rare condition in which the body makes too much urine. It occurs because the body doesn’t have enough of or does not respond normally to a hormone called vasopressin, also called arginine vasopressin (AVP) or antidiuretic hormone (ADH). 

Arginine vasopressin is responsible for making concentrated urine by only absorbing the water from the urine. Deficiency of or resistance to this hormone affects the body’s ability to regulate fluid balance, allowing large quantities of diluted urine to be passed from the body. This makes you feel thirsty because the body loses excess fluids in urine. 

Diabetes insipidus is also called arginine vasopressin deficiency or arginine vasopressin resistance.

What is Diabetes Mellitus?

Diabetes mellitus is a common condition in which the body is unable to regulate blood sugar, leading to high blood glucose levels. It occurs because the body doesn’t have enough of or does not respond normally to the hormone insulin. 

Insulin is responsible for moving glucose (sugar) out of the bloodstream and into cells, where it is used for energy. Deficiency or resistance to insulin hormone causes glucose to remain in the blood, leading to hyperglycemia or high blood sugar. 

Diabetes mellitus is often simply called diabetes.

What Is The Main Difference Between Diabetes Mellitus and Diabetes Insipidus?

While diabetes insipidus and diabetes mellitus sound similar, they are separate medical conditions and are not connected in any way. The main difference is that diabetes insipidus is a rare form of diabetes in which the kidneys make too much urine, while diabetes mellitus is a common condition in which blood sugar levels remain elevated.

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Symptoms of Diabetes Insipidus and Diabetes Mellitus

Common Symptoms of Diabetes Insipidus

• Urinary frequency (needing to urinate more often)

• Polyuria (passing large amounts of dilute or light-colored urine)

• Polydipsia (excessive thirst causing you to drink fluids very often or suck on ice chips all the time)

Common Symptoms of Diabetes Mellitus

• Polydipsia (increased thirst)

• Polyuria (increased urination)

• Polyphagia (increased hunger)

• Fatigue

• Blurred vision

• Numbness or tingling in the hands or feet

• Slow healing wounds

• Unexplained weight loss

What Are The 3 P's of Diabetes Insipidus?

The 3 Ps are actually symptoms of diabetes mellitus and not diabetes insipidus. The triad of symptoms in diabetes mellitus - polydipsia (excessive thirst), polyuria (excessive urination), and polyphagia (excessive hunger) - is often referred to as the 3 Ps.

The three main symptoms of diabetes insipidus are polyuria (increased urine volume), frequent urination (needing to pee often), and polydipsia (increased thirst).

Why is Diabetes Insipidus Called Diabetes?

“Diabetes” is a Greek word that means siphon, which is “to pass through.” For these two health conditions, “diabetes” is used in the context of “urine.” “Mellitus” is another Latin word that means sweet and describes the sweeter urine odor of those with diabetes mellitus. On the other hand, “insipidus,” another Latin word, means tasteless to describe the clear, odorless, diluted urine from those with diabetes insipidus.  

Notably, diabetes insipidus and diabetes mellitus are different conditions and have different additional symptoms, causes, and treatments.

Causes and Risk Factors

Causes of Diabetes Insipidus

The main cause of diabetes insipidus is a problem with the hormone vasopressin that helps the kidneys maintain fluid levels and sodium levels in the body. The exact cause depends on the type of diabetes insipidus.

Central Diabetes Insipidus 

Central diabetes insipidus, also called cranial diabetes insipidus, occurs when the body doesn’t make enough vasopressin. This hormone is made by a part of the brain called the hypothalamus. Damage to the hypothalamus or pituitary gland from a head injury, brain tumor, autoimmune disorders, brain surgery, and inherited gene mutations can cause central DI.

Nephrogenic Diabetes Insipidus 

Nephrogenic diabetes insipidus (DI) occurs when the body makes enough vasopressin, but the kidneys don’t respond to the hormone the way they should, resulting in too much fluid eliminated in urine. This can happen due to side effects of certain medications used to treat psychotic disorders, a blockage in the urinary tract, hypercalcemia (high blood calcium levels), hypokalemia (low blood potassium levels), and inherited disorders. Rarely, kidney problems like chronic kidney disease can cause nephrogenic DI and increase the amount of urine the kidneys produce.

Dipsogenic Diabetes Insipidus 

Dipsogenic diabetes insipidus, also called primary polydipsia, occurs due to damage to the hypothalamus from infection, head injury, inflammation, or tumors. It can also occur following surgery, the use of certain medicines, and in people with certain mental health conditions such as schizophrenia. These conditions affect the thirst mechanism and cause you to feel more thirsty and drink more fluids (polydipsia). The excess fluid intake leads to excess urine production. 

Gestational Diabetes Insipidus 

Gestational diabetes insipidus is a rare and temporary condition that occurs when a pregnant woman’s placenta makes too much of an enzyme that breaks down vasopressin. Women carrying more than one baby have more placental tissue and are at a higher risk. Preeclampsia and HELLP syndrome can also increase the risk of gestational DI by affecting liver function.

Causes of Diabetes Mellitus

The main cause of diabetes mellitus is a problem with the hormone insulin, which helps to move glucose from the blood to the cells. The exact cause depends on the type of diabetes mellitus.

Type 1 Diabetes Mellitus

Type 1 diabetes mellitus is an autoimmune reaction in which the body’s immune system attacks and destroys beta cells in the pancreas that produce insulin hormone. This results in the body not having enough insulin, leading to high blood sugar levels. The exact cause is unknown, but scientists believe it is a combination of genetic and environmental factors, including viral infections.

Type 2 Diabetes Mellitus

Type 2 diabetes mellitus is the most common type of diabetes. It occurs due to both genetic and lifestyle factors. Risk factors for type 2 diabetes include being overweight or obese (especially having belly fat), a lack of physical activity, high blood pressure, and high cholesterol. Diabetes mellitus type 2 usually starts with insulin resistance, where the cells in the body do not use or respond to insulin as they should. Genes also play a role, and diabetes mellitus type 2 is more common in certain ethnic groups.

Gestational Diabetes Mellitus

Gestational diabetes mellitus is a temporary condition in which there is too much glucose in the blood during pregnancy. It occurs due to hormonal changes as well as lifestyle and genetic factors. Discover how to monitor diabetes during pregnancy.

Diagnosis

Diagnostic Tests for Diabetes Insipidus

• Urine tests: Testing urine concentration and measuring urine volume can help to diagnose diabetes insipidus. Healthy people make 1 to 3 liters of urine a day, while people with diabetes insipidus can make up to 19 liters of dilute urine a day.

• Blood tests: CMP (comprehensive metabolic panel) or BMP (basic metabolic panel) can be used to check electrolyte levels in the blood (sodium, potassium, calcium, magnesium, phosphorus) can help to identify the type of diabetes insipidus.

• Water deprivation test (Miller-Moses test): This test is done to diagnose DI. It evaluates how your body responds to the lack of fluids. Your healthcare provider will measure urine volume, urine concentration, changes in body weight, and blood ADH level after withholding fluids for several hours. You may also receive synthetic ADH hormone to see if your kidneys respond to the hormone.

• Imaging studies: Your healthcare provider might order magnetic resonance imaging (MRI) to look for problems in the hypothalamus and pituitary gland in the brain. 

• Genetic testing: If you have a family history of diabetes insipidus, your provider may recommend getting testing to check for mutations in genes linked to nephrogenic diabetes insipidus.

Diagnostic Tests for Diabetes Mellitus

• Hemoglobin A1c: This blood test, also called the glycated hemoglobin test, is a measure of the average blood sugar levels over the past 2 to 3 months. A1C below 5.7% is considered normal. A1C between 5.7% and 6.4% indicates prediabetes. If your A1C level is 6.5% or higher on two separate tests, you will receive a diagnosis of diabetes. 

• Fasting blood sugar test: This blood test is done after fasting (not eating anything) overnight. A fasting blood glucose level below 100 mg/dL (milligrams per deciliter) is normal. FBS between 100 and 125 mg/dL indicates prediabetes. Any value above 126 mg/dL on two separate tests means you have diabetes.

• Random blood sugar test: This is done on a blood sample taken at a random time, regardless of your last meal. A blood glucose level of 200 mg/dL or higher indicates diabetes.

• Glucose tolerance test: This test is done after overnight fasting. Your fasting blood sugar is measured. You then drink a sugary liquid and have your blood sugar tested over the next two hours. Blood sugar below 140 mg/dL is normal. A result between 140 and 199 mg/dL indicates prediabetes. A value above 200 mg/dL after two hours indicates diabetes. 

• Urine ketones: This test is done in people with suspected type 1 diabetes mellitus. Ketones are byproducts of the body using fat instead of glucose for energy. 

• Blood test for autoantibodies: Your healthcare provider may order a test to see if you have certain autoantibodies in your blood. High levels may indicate type 1 diabetes.

Which Is The Best Test To Differentiate Between Diabetes Insipidus and Diabetes Mellitus?

The key diagnostic tests for diabetes insipidus and diabetes mellitus are different because they measure different things in the body. Both diabetes insipidus and diabetes mellitus can cause increased thirst and increased urination. However, diabetes insipidus doesn't affect blood sugar, while diabetes mellitus does. 

Treatment Options

Diabetes Insipidus Treatment

• Treatment for dehydration: Mild diabetes insipidus can be treated by drinking more water to prevent dehydration due to fluids lost in urine. 

• Desmopressin: A synthetic form of vasopressin hormone called desmopressin (DDAVP, Nocdurna) is available as a pill, nasal spray, and injection. It is used to treat central diabetes insipidus and gestational diabetes insipidus.

• Low-salt diet: Nephrogenic diabetes insipidus is treated with a low-salt diet to lower urine production by the kidneys. 

• Hydrochlorothiazide (Microzide): Hydrochlorothiazide is a diuretic (water pill) and typically increases urine output but can reduce urine formation in some people with nephrogenic diabetes insipidus.

• Other treatments for diabetes insipidus include treating the cause (for example, brain surgery to remove a tumor) or stopping medicines causing the problem. 

Diabetes Mellitus Treatment

• Insulin: People with type 1 and type 2 diabetes mellitus are treated with insulin injections or insulin pumps along with carbohydrate counting and regular blood sugar monitoring. Many types of insulin are available, including short-acting, rapid-acting, intermediate-acting, and long-acting insulin. You may need to use different insulin types throughout the day.

• Oral diabetes drugs: People with type 2 diabetes are treated with oral diabetes drugs, insulin, or both, alongside lifestyle changes, carbohydrate counting, and blood glucose monitoring. Metformin (Fortamet, Glumetza, others) is usually the first drug prescribed to people with type 2 diabetes. There is currently no oral medication available to treat type 1 diabetes.

Ongoing Management and Monitoring

According to the National Institute of Diabetes and Digestive and Kidney Diseases, blood sugar levels can be unpredictable because they are affected by various factors, including diet, physical activity, illness, hormonal changes, medications, and mental stress. Your diabetes care team will work with you to develop a treatment plan for careful management of your diabetes and blood glucose levels. 

Living With Diabetes Insipidus and Diabetes Mellitus

Diet and Nutrition

Treatment for all types of diabetes includes healthy lifestyle changes, including a healthy diet and regular exercise. Your healthcare team will give you further tips on diet and nutrition based on the type of diabetes. 

For example, if you have type 2 diabetes mellitus, a healthy eating plan should include eating more fresh fruits, vegetables, whole grains, and low-fat dairy and avoiding processed foods and foods and beverages with added sugar. 

If you have diabetes insipidus, your healthcare providers may recommend eating a low-salt diet and drinking more fluids to prevent severe dehydration.

Lifestyle Adjustments 

Lifestyle changes for diabetes include healthy eating, regular physical activity, weight loss if you are overweight or obese, smoking cessation, limiting alcohol intake, and managing stress.

Tips for Caregivers of People with Diabetes

• Learn about diabetes, including the difference between diabetes insipidus and diabetes mellitus.

• Ask your loved one how you can help and listen to them. Their needs can change over time. 

• Encourage a healthy lifestyle and good food choices. 

• Help with medical appointments. 

• Remind your loved one to check their blood sugar levels and take their medications on time. 

• Join a loved one who has diabetes in an exercise program to provide motivation and encouragement.

• Plan for emergencies and diabetes-related health complications.