[Diabetes Pt.3] Laboratory Investigations in Diabetes

Read part 1 of this article: Diabetes; Known or Unknown?

Diabetes presents with very high glucose levels in blood. It is essential that every individual does a regular check on the blood glucose levels.

The more routine laboratory investigations for diagnosis of diabetes are fasting blood glucose (FBG), random blood glucose (RBG) and urine glucose tests. The less routine investigations include 2-hour post prandial (2-hr PPG) and oral glucose tolerance tests (OGTT). Glycated Hemoglobin (HB A_1C) test is relegated for the management of diabetes.

Read part 2 of the article: Is Diabetes Manageable?

The FBG test is the most common method used in diagnosis. It measures the amount of glucose in the blood after fasting for 8-12 hours. After the fast: Normal blood glucose level should be between 3.6-5.9mmol/L; Blood glucose level of 6.0-6.9mmol/L is referred to as border line and individuals with such levels stand the chance of developing diabetes in the future; Blood glucose level greater than 7.0mmol/L is deemed hyperglycemia (above normal glucose level) and could be as a result of diabetes. The same idea is employed in the RBG test, except that fasting is not a prerequisite of this test. The reference ranges for the RBG are therefore different (a little higher) than those of the FBG. When the blood glucose reaches a threshold (usually above 11mmol/L), it starts appearing in urine. This is when the urine glucose test is employed in telling if one is diabetic.

The 2-hr PPG and OGTT tests are based on the same principle; how glucose is responded to and regulated by an individual’s system. If they are to be done, they are commenced right after a routine FBG which gives a base line. For the 2-hr PPG, the individual is given a carbohydrate laden meal and blood samples taken every 30minutes for blood glucose measurement for 2 hours. For the OGTT, the individual is given glucose solution (usually 70g of glucose in 300mls of water) and blood samples taken every 1hour for blood glucose measurement for 3 hours. The OGTT test has replaced the 2-hr PPG since it is more sensitive and controlled. A curve is drawn from a graph of glucose level against time and compared to the normal for inferences to be made.

The HB A_1C test is used in monitoring the blood glucose levels over 3-4months. HB A_1C is basically hemoglobin with bound glucose. In diabetics, the high level of blood glucose induces the binding of some of the glucose to hemoglobin. The life span of red blood cells is 120days. When a diabetic with high HB A_1C starts a management regimen, the regimen is deemed effective if after 3-4months (approximation of 120days), the HB A_1C comes down to reduced or normal levels. This is because in 3-4months, new red cells would have replaced the old ones and being exposed to the low levels of blood glucose due to the regimen, there wouldn’t be inducement for binding. However, if the regimen is ineffective, the HB A_1C level remains high after 3-4months because the new red cells would still be exposed to high levels of blood glucose, and binding of glucose to hemoglobin would be induced.

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This article was written by Joseph Ofori and reviewed by Arnold Agyapong Prempeh, both professional Medical Laboratory Scientists.