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Diabetes Mellitus Laboratory Tests

What is diabetes mellitus?

Diabetes mellitus is a medical condition in which the amount of glucose in the bloods is highly elevated. Currently, about 3.5 million people in Malaysia are diagnosed with this disease.

Types of diabetes mellitus?

  • Insulin dependant diabetes mellitus, commonly known as type 1 diabetes mellitus.
  • Non-insulin dependant diabetes mellitus, commonly known as type 2 diabetes mellitus.
  • Gestational diabetes.

What are the laboratory tests used for diagnosis of diabetes mellitus?  

RBS (Random Blood Sugar)

This test measures blood sugar level at random. This means sampling is done at anytime of the day regardless of diet taken. The normal range for random blood glucose is 7.8 mmol/L – 11.1 mmol/L. Random blood glucose results is usually not used as a diagnostic test for diabetes mellitus.

FBS (Fasting Blood Sugar)

Blood sample for this test is taken after an 8-12 hours or overnight fasting. Water intake is allowed during this fasting period. A healthy individual would expect its blood glucose level to increase during fasting and rebalanced back to normal levels by the insulin hormone. A diabetic patient would have problems rebalancing the glucose level causing blood glucose levels to remain elevated.

Fasting blood glucose levels of above 7.0 mmol/l is an accepted criteria for diagnosis of diabetes mellitus. If the patient has symptoms of the disease, FBS of more than 7.0 mmol/L in one occasion is sufficient for diagnosis. However, FBS must be elevated twice to confirm diagnosis if the patient is without any symptom of the disease.

OGTT (Oral glucose tolerance test)

This test is usually performed on individuals who have a normal FBS values but are presented with clinical symptoms of diabetes such as glycosuria (glucose in the urine), polyuria (frequent urination) and polydipsia (always feeling thirsty).

The test is done by taking a blood sample either twice or thrice. The first blood drawn is for measurement of the FBS value. Then, the patient is given a glucose drink containing 75 g of glucose. The second (1-hour post prandial) and third blood samples (2-hour post prandial) are taken at 60 and 120 minutes after the glucose drink. Currently, it is usual to take a fasting and 2-hour post prandial sample.

The principle of this test is to evaluate the ability of our body to absorb and rebalance the glucose ingested.

Normal healthy individual
(mmol/L)

Impaired glucose tolerance
(mmol/L)

Diabetic
(mmol/L)

FBS

< 7.0

< 7.0

? 7.0

2-HPP

< 7.8

7.8 – 11.1

? 11.1

What are the laboratory tests used for monitoring for treatment of diabetes mellitus?

HbA1c (glycated hemoglobin)

This test is used to monitor the effectiveness of your blood glucose control. This test measures an average level of blood glucose over the previous three months. This test does not require fasting and a blood sample can be drawn at any time of the day.

Hemoglobin is a protein in red blood cells that carries oxygen. Glycated hemoglobin forms when glucose binds to hemoglobin. Since red blood cells circulate in the system for at least 120 days, HbA1c test provides an accurate indication of blood glucose levels for the past three to four months.

An individual with good blood glucose control should have HbA1c levels of less than 6.5%.

Fructosamine

This test is used to monitor blood glucose levels in patients who have red blood cell abnormality. These include anemic, sickle-cell anemic and thalasaemia patients.

The difference between this test and HbA1c test is that instead of measuring glycated hemoglobin, glycated protein is measured. Since protein in remains in blood for 14-21 days, this test measures the blood glucose average for this period.

This test is sometimes also ordered for pregnant women who have gestational diabetes because changes can happen very quickly in pregnancy.  This test can also be done to monitor effectiveness of new treatments if there is recent change in medications administered.

The normal range for fructosamine is 1.5 -2.5 mmol/L

Urinary Glucose

This test measure the amount of glucose found in urine, a medical condition termed glycosuria. This test is usually done using a test strip that will produce colour change after reaction with glucose. This test can be also done from home using a test kit.

(a)
(b)

(c)

  1. Dripping the test pad
  2. Time exactly
  3. Compare the test pad colour

Glucose is usually not found in urine. Only individuals with high blood glucose levels will produce overflow of glucose into urine. However, pregnant ladies and individuals with impaired renal function might have traces of glucose in their urine. This makes urine glucose measurement difficult to interpret. Thus, blood glucose level is still the preferred test for diabetes diagnosis and monitoring.

How to monitor blood glucose levels from home?

Blood glucose levels can be easily monitored from home using a device called the glucometer. This device uses whole blood sample usually drawn from a finger prick. The accuracy of glucometer performance depends on several factors

  • Variability in patients technique
  • Presence of interfering substance such as high triglyceride concentration and some drugs
  • Presence of anemia(causes false results)
  • Defective reagent strips and malfunction of devices
  • Lack of correlation between different brands of glucometers

Thus, it is advised that regular routine laboratory glucose analysis is done on diabetic patients to provide a better picture of blood glucose control.

References

  1. (1997-2011).Retrieved June 20, 2013, from Malaysian Diabetes Association: http://www.diabetes.org.my
  2. (1995-2013). Retrieved June 20, 2013, from American Diabetes Association: http://www.diabetes.org/
  3. Evelyn SC Koay, N. W. (1996). A Primer of Chemical Pathology. Singapore: World Scientific Publishing Co Pte Ltd.
Last Reviewed : 3 January 2014
Writer : Kanchana a/p Kanthasamy

 

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