What Is Diabetes Insipidus?

When most people hear " diabetes," they think of diabetes mellitus. That's a condition in which blood sugars are chronically elevated. In fact, diabetes is a general term for conditions that cause increased urine production. And when it comes to increased urine production, diabetes insipidus takes the cake.

Diabetes insipidus results in excessive thirst and urination. The reason is problems with a particular hormone or its receptor. Diabetes insipidus increases the risk for dehydration. Here, WebMD takes a look at this uncommon and inconvenient medical condition.

What Is Diabetes Insipidus?

Diabetes insipidus is caused by problems related to a hormone called anti-diuretic hormone or its receptor. Anti-diuretic hormone (ADH) is produced in a part of the brain called the hypothalamus. It's stored in the brain's pituitary gland. Release of ADH causes the kidneys to hold onto water, which makes urine more concentrated.

Normally, if we are thirsty or slightly dehydrated, ADH levels rise. The kidneys reabsorb more water and excrete concentrated urine. If, on the other hand, we chugged a half-gallon of water (don't try this at home), ADH levels would fall. Clear, dilute urine would pass.

Diabetes insipidus can be caused by either of two problems with ADH. One is too little ADH is produced. When that's the case, the condition is called central diabetes insipidus. The other is there's enough ADH produced, but the kidneys can't respond to it. That condition is known as nephrogenic diabetes insipidus.

In either form of diabetes insipidus, the result is the same. The kidneys can't do their job of conserving water. Even when a person with diabetes insipidus is dehydrated, the kidneys will excrete abundant, dilute urine.

This inability of the kidneys to conserve water leads to the symptoms of diabetes insipidus:

• Excessive thirst
• Excessive urine production (polyuria)

In some people, these symptoms can become extreme, causing dehydration.

Excessive fluid losses can also cause electrolyte imbalances. Possible symptoms include:

• Unexplained weakness
• Lethargy
• Muscle pains
• Irritability

But why "insipidus?" People with diabetes insipidus aren't insipid, but their urine is. Insipid can mean dull or lacking flavor. Believe it or not, doctors long ago would taste urine to detect illness. Unlike diabetes mellitus, which results in sweet tasting urine, diabetes insipidus creates watery, flavor-free urine.

How Is Diabetes Insipidus Diagnosed?

People with diabetes insipidus often seek medical attention because of their symptoms of excessive thirst and urination.

Diagnosing diabetes insipidus requires serial measurements of blood and urine in a doctor's office over several hours. The person goes without water during this time and gets progressively thirstier. The concentrations of sodium in the blood and urine are determined over time. An ADH substitute might then be administered to see if the person's kidneys respond to it by concentrating the urine. The laboratory values and response to ADH can make the diagnosis.