Diabetes insipidus diagnosis

If your healthcare provider believes that you may have diabetes insipidus, he or she will likely conduct testing to determine whether you have the condition.

Some of the tests¹⁴ used to diagnose diabetes insipidus include:

• Water deprivation test: This test determines whether your body is producing enough ADH and whether your kidneys can respond normally to ADH. When you restrict your fluid intake, ADH allows your kidneys to decrease the amount of fluid lost in the urine to prevent you from becoming dehydrated.

During this test, you will be asked to stop drinking fluids for several hours while being closely monitored by a healthcare provider or team. While fluids are being withheld, your provider will measure any changes in your body weight, urine output, and the concentration of your urine and blood. He or she may also measure the levels of ADH in your blood or administer synthetic ADH during the test.

• Magnetic resonance imaging (MRI): This noninvasive test uses a powerful magnetic field and radio waves to construct detailed pictures of pituitary gland abnormalities that may cause diabetes insipidus, along with imaging of brain tissue. MRIs can look for abnormalities in or near the pituitary gland.
• Genetic screening: If other members of your family have had problems with excess urination, it may be suggested that you undergo genetic screening.

Diabetes diagnosis

If your provider believes that you may have diabetes types 1 or 2, he or she will likely conduct a series of tests that measure your blood sugar levels.

One common form of testing for diabetes is a glycated hemoglobin test. This blood test, commonly called an A1C test, indicates your average blood sugar level over the past 2–3 months.

An A1C below 5.7% is considered normal. An A1C between 5.7–6.4% indicates prediabetes, while an A1C of 6.5% or higher on two separate tests indicates diabetes.

In some cases, the results from A1C tests alone may not be enough to diagnose diabetes. The results may be inconsistent, or you may have a health condition that can make the A1C test inaccurate (such as if you are pregnant¹⁵, as A1C levels can be falsely low in the 2nd trimester, but may rise in the 3rd trimester). Sometimes the test may be unavailable.

If A1C tests alone are not sufficient to provide a diagnosis, the following tests may be used to diagnose diabetes:

• Random blood sugar test: In this test, a blood sample is taken at a random time. A blood sugar level of 200 milligrams per deciliter (mg/dL)—or 11.1 millimoles per liter (mmol/L)—or higher suggests diabetes.
• Fasting blood sugar test: This test involves taking a blood sample after you have fasted overnight (no food or liquids besides water for at least 8 hours). A fasting blood sugar level less than 100 mg/dL (5.6 mmol/L) is considered normal. A fasting blood sugar level from 100–125 mg/dL (5.6–6.9 mmol/L) is considered prediabetes, while 126 mg/dL (7 mmol/L) or higher on two separate tests indicates diabetes.
• Oral glucose tolerance test: Oral glucose tests are most commonly used to diagnose diabetes in pregnancy (gestational diabetes). In some cases, they may be used as a screening tool to help diagnose type 2 diabetes. These tests involve taking a blood sample after fasting for at least 8 hours (or overnight). The patient is then given a sugary solution to drink and blood sugar levels are generally drawn 1–3 hours later, as directed by a provider. In general, a blood sugar level from 140–199 mg/dL (7.8–11.0 mmol/L) indicates prediabetes.