Diabetes Test: Diagnosis and Further Examinations

To diagnose diabetes mellitus, various examinations are available. In addition, the examination of the nerves and vessels, as well as the organs for which a high blood sugar is particularly dangerous, has an extremely important significance. Here it is necessary to check whether damage has already occurred. Which tests are useful for the diagnosis of diabetes and which further examinations should be carried out, you can find out here.

Examinations for diabetes

If diabetes mellitus is suspected on the basis of the typical symptoms, those affected should first visit their family doctor. He or she can perform appropriate tests and examinations to establish the diagnosis of diabetes. The following examination options are available:

  • Anamnesis (inquire about medical history): complaints such as increased urination and great feeling of thirst can provide information about how long the diabetes has existed undetected.
  • Urine examination: with the help of a test strip, the urine sugar can be determined. If sugar is excreted in the urine, this is an indication of increased blood sugar levels and thus the presence of diabetes. However, this quick test can only serve to confirm an initial suspicion, while a negative result does not allow the disease to be ruled out: often the kidneys do not immediately excrete sugar with the urine despite an elevated blood sugar level. The so-called renal threshold is about 8.9 to 10 mmol/l (160 to 180 mg/dl).
  • Blood tests: Greatest importance for diabetes diagnostics has the repeated blood glucose determination. Here, the blood glucose value (fasting, after eating and after taking glucose) must be considered and also the blood glucose long-term value (HbA1c) is checked repeatedly in the course of the disease.
  • Antibody test: a test for so-called autoantibodies (a characteristic feature of autoimmune diseases) can be performed if it is unclear what form of diabetes it is. While such autoantibodies can be detected in type 1 diabetes before the first symptoms appear, they are not present at all in type 2.

Blood glucose measurements: four important tests.

The most important tests for the diagnosis of diabetes are the measurements of the different blood glucose levels. In the course of the disease, blood glucose levels also play a special role, because properly adjusted blood sugar helps to avoid secondary diseases. A distinction is made between four types of blood glucose tests. What do these tests say and what limits apply?

HbA1c value (long-term blood glucose value).

The HbA1c value is used to describe the average blood glucose concentration over the past eight to 12 weeks. A blood sample taken fasting, i.e. before eating, is required for determination. The following limits apply:

  • Below 39 mmol/mol (below 5.7 percent): no diabetes.
  • 39 to 48 mmol/mol (5.7 to 6.5 percent): prediabetes (a possible precursor of diabetes)
  • More than 48 mmol/mol (more than 6.5 percent): diabetes.

If the values are in the middle range, the test result allows neither exclusion nor reliable confirmation of diabetes mellitus. In this case, further tests are performed.

Fasting blood glucose value

To determine the fasting blood glucose level, a blood sample is taken in the morning, after abstaining from food for at least eight hours. The glucose level in venous plasma is determined. The following values apply:

  • Below 100 mg/dl (below 5.6 mmol/l): no diabetes.
  • 100 to 126 mg/dl (5.6 to 7 mmol/l): prediabetes (depending on the source, a minimum value of 110 mg/dl (6.1 mmol/l) applies here.
  • More than 126 mg/dl (more than 7 mmol/l): diabetes.

Again, test results in the middle range only indicate impaired glucose tolerance. In this case, an oral glucose tolerance test should be performed.

Oral glucose tolerance test (oGTT).

This test provides information about how well sugar from food is absorbed into cells. Normally, insulin in the body ensures that sugar is absorbed from the blood into the body’s cells, causing blood glucose levels to drop quickly. In diabetes, this process is disturbed and the blood glucose level remains elevated for longer. In the oGTT, a sugar solution containing 75 grams of sugar is drunk on an empty stomach (it is usual to abstain from food and cigarettes for eight to twelve hours).A blood sample is taken at the beginning and after two hours. For the values at the beginning, the fasting blood glucose values already mentioned apply. Here’s what the oGTT 2-hour values tell you:

  • Less than 140 mg/dl (7.8 mmol/l): no diabetes.
  • 140 to less than 200 mg/dl (7.8 to less than 11.1 mmol/l): prediabetes
  • Greater than or equal to 200 mg/dl (11.1 mmol/l): diabetes

This test plays only a minor role in the diagnosis of type 1 diabetes.

Occasional blood glucose

The so-called casual blood glucose, which is measured in venous plasma in a non-fasted state, can also contribute to the diagnosis of diabetes if symptoms are already present. The cutoff value is 200 mg/dl (11.1 mmol/l) or higher. However, results should be further corroborated by determination of the oGTT value or fasting blood glucose.

Further investigations in cases of organ damage

When a diagnosis of diabetes is pronounced, all organs for which high blood glucose is particularly harmful should be examined for preexisting damage. Elevated blood glucose levels damage our body’s organs in different ways. The large blood vessels in which the too “sugary” blood flows tend to harden arteries and then promote high blood pressure and, in the worst case, a heart attack, further heart problems or a stroke. Other organs can also suffer a heart attack. But the kidneys (diabetic nephropathy) and eyes (diabetic retinopathy) can also be damaged by the vascular damage. Poor blood flow also affects the smallest nerve endings (diabetic polyneuropathy). In diabetics, the nerves are consequently less sensitive to stimuli, which, especially in the feet, together with poor circulation, can quickly lead to the clinical picture of diabetic foot. This susceptibility to infections also manifests itself in other parts of the body, for example in the form of dental inflammation or fungal infections. A careful eye examination, a kidney function test, an ECG for heart function and an examination of leg blood flow and nerve function are indispensable to get an overview of failures or dysfunctions.

Regular checkups are important

To avoid secondary diseases or to detect them in time, diabetics should undergo regular medical check-ups. These include:

  • The HbA1c value and blood glucose (fasting and after eating).
  • The so-called microalbuminuria test to detect proteins in the urine, which may indicate kidney damage
  • The control of the feet for ulcers or injuries and the leg vessels.
  • Neurological examinations
  • The cholesterol levels
  • The serum creatinine level
  • A heart control by means of ECG
  • An examination of the eyes by an ophthalmologist

Gestational diabetes means danger for mother and child. Such a pregnancy is always classified as a high-risk pregnancy and must be specially monitored.

Self-monitoring in diabetes

In addition, diabetics themselves should carry out regular self-monitoring. Important here are:

  • Blood pressure
  • Body weight
  • Urine sugar level
  • Blood glucose value
  • Acetone value in urine

Checking the urine for the substance acetone can detect metabolic derailments that can lead to diabetic coma. Acetone determination can be done with a special test strip. In addition, the feet should be checked daily to prevent diabetic foot.