Common Laboratory Tests Performed to Confirm Diagnosis of Diabetes Mellitus

The diagnosis of Diabetes Mellitus (DM) comes from careful evaluation of the patient's history, the physiologic symptoms and the clinical laboratory results. The clinical laboratory performs the required tests on an appropriate patient's sample and the results would then be used to confirm the diagnosis of DM.

The following are laboratory results that could confirm DM in a patient:

1. Glucosuria

This is the presence of glucose (sugar) in urine. The urine specimen would be positive for sugar.

The renal threshold for glucose is 160 mg/dL. When this concentration is exceeded in the blood, then it would then appear in the urine making the urine specimen positive for sugar. This is an indication that the concentration of glucose in blood could be more than 160 mg/dL.

2. Ketonuria

Presence of ketone bodies (acetone, hydroxybutyric acid, etc) in urine. This indicates that the body could not utilize the carbohydrates as a source of energy because of the insufficiency of insulin; so it makes use of lipids (fats) instead. The utilization of fats as a source of energy will lead to an increase concentration of the by-product of lipid which are the ketone bodies. These will then lead to the increased excretion of ketones in the urine called ketonuria.

3. Hyperglycemia

This leads to the increased levels of sugar, predominantly glucose, in the blood stream. This could be detected by allowing the patient to fast for 8 to 12 hours before collection of blood specimen. A patient with a sample value above the normal which is 60-110 mg/dL (Orthotoluidine method), would be considered as hyperglycemic and a candidate for DM.

Oral Glucose Tolerance Test (OGTT) could also be performed on a patient suspected of DM.

1. A fasting baseline blood sample is obtained.
2. A glucose challenge (solution) which may be oral or intravenous is given to the patient.
3. A 30-minute, 1 hr, and 1 & ½ hr- blood samples is then obtained from the patient. The frequency will depend upon whether it is a single-oral dose or a multiple dose method.
4. Interpret the results depending upon the method selected.
5. Generally, two hours after the glucose load or challenge is taken in, the blood concentration should go back to normal levels.

Hemoglobin A1C

This is a test for the patient's adherence to his medications for DM. If the patient did not adhere to his medications, then the value of this type of hemoglobin is usually elevated.

These are the most common laboratory tests performed to confirm the diagnosis of diabetes mellitus. It is imperative therefore, that these tests are performed reliably under the expertise of a licensed Medical Technologist or Clinical Laboratory Scientists.