Blood Glucose Testing

The blood glucose is a very commonly performed test to look at the levels of blood sugars in the body. Individuals may have high or low blood sugars from several causes and it is important to pick up on these as many have very adverse outcomes. Diabetes Mellitus is the most common cause of high blood sugars and regular testing of glucose is essential for effective management of the disease.

Causes of High Blood Sugars (Hyperglycemia)

1. Type 1 DM: This type is associated with a complete absence of insulin production by the pancreas. This is believed to occur from an auto-immune mediated destruction of the cells producing insulin (beta-cells). This generally presents earlier in life usually the teens and requires insulin for survival.
2. Type 2 DM: This type is associated with insulin resistance. This occurs when higher and higher levels of insulin are required for the body’s cells to take up glucose, eventually becoming insensitive. This is the more common type of DM which is associated with obesity and unhealthy eating practises.
3. Gestational Diabetes Mellitus: This is a condition involving high blood sugars in pregnant women. This occurs due to  abnormal metabolism of glucose with development of insulin resistance. Generally, the hyperglycemia resolves after child birth, but these women have a higher risk of developing DM later in life.
4. Chronic Steroid Use: Long term use of steroids like prednisone are associated with breakdown and release of stored glucose within the cell leading to hyperglycemia.
5. Glucagon excess: A tumor of the cells producing glucagon in the pancreas, called glucagonoma, can lead to excess breakdown of stored glucose to cause hyperglycemia. This is a relative rare condition and is associated with other systemic manifestations such as skin rash and anemia.

Causes of Low Blood Sugars (Hypoglycemia)

1. Hypoglycemic spells in Diabetic individuals: Patients receiving therapy for DM wither with insulin or oral drugs are at risk for falls in blood sugar if they do not eat food adequately. This is associated with symptoms of faintness, sweating, tremors and a racing heartbeat.
2. Insulinoma: This is a tumor of the insulin producing beta cells in the pancreas. This causes very significant falls in the blood glucose levels  with the symptoms described above.
3. Alcohol intake: Individuals who drink large quantities of alcohol are generally deprived of calorie rich food with risk of hypoglycemia

Measuring blood glucose

Different methods are used to measure blood glucose levels, these are:

1. Plasma glucose measurement: This is the method more frequently performed and is generally more accurate. Any diagnosis of diabetes is made from results of plasma blood glucose.
2. Capillary blood glucose measurement: This is a rapid finger stick method which gives instant results. The accuracy is not as good as the plasma method. This is very useful for quick assessment of glucose levels in an emergency setting. It is also used for screening purposes in a large population.

Testing for Diabetes and Hyperglycemia

The American Diabetes Association has recommended screening for the following groups:

1. Any person having a BMI (body mass index) over 25 (for people of Asian origin, BMI over 23) should be screened for diabetes as obesity increases the risk of insulin resistance.
2. Everyone over the age of 45 years: All individuals should be screened after the age of 45 years and if confirmed negative, should be tested every 3 years.
3. All women with history of gestational diabetes should be screened every 3 years
4. Patients who have been diagnosed with prediabetes should be tested annually. Pre-diabetes refers to when a person has high blood sugars which are however below the cut-off for diagnosing diabetes mellitus.

Tests Performed to diagnose Diabetes

1. Random Blood Glucose Test: This is a blood test taken at any time of the day to test for blood glucose. A value over 200 milligram/decilitre (mg/dl) at any time or over 11.1 millimoles/litre (mmol/L) is diagnostic of Diabetes
2. Fasting Blood Glucose Test: This test is performed in the morning on an empty stomach after fasting overnight. Normal blood sugar is defines as less than 100 mg/dl (5.6mmol/L). Levels between 100 and 125 mg/dl (5.6 to 6.9 mmol/L) is considered to be prediabetic. A fasting blood sugar level equal to or higher than 126 mg/dl (7 mmol/L) on 2 separate occasions is diagnostic of Diabetes Mellitus.
3. HbA1c Testing: this is a blood test to look for glycated haemoglobin. When there is a prolonged elevation of blood glucose, it binds to the haemoglobin in red blood cells. As red cells have a life span of 120 days, the HbA1C levels can provide an estimate of blood sugar control over 3 months. Having a value less than 5.7% is normal. An A1C level over 6.5% on 2 separate occasions is suggestive of diabetes and anything in between indicates prediabetes

Testing for Hypoglycemia

Patients with symptoms suggestive of low blood glucose should immediately be tested using the capillary glucose testing to establish low sugars. The treatment of the low sugars with oral glucose solutions or intravenous glucose should be initiated while awaiting the results of the plasma glucose.

A plasma glucose level less than 45-50mg/dl (2.5-2.8 mmol/L) is usually defined as hypoglycaemia.

If this occurs frequently in a diabetic patient, continuous glucose monitoring can be done using a permanent intravenous probe to regularly check glucose levels.

At a later time, the cause of hypoglycaemia should be evaluated

1. Insulin assay: This is a test to identify the levels of insulin In the blood. A high level may suggest overdose of insulin or diabetic medications; possibility of insulinoma should also be considered.
2. C-peptide: This is elevated in the case of insulinomas and ingestion of insulin releasing drugs (eg: sulphonylureas). The urine may be tested for these drugs if abuse is suspected

References:

1. Diabetes Tests & Diagnosis | NIDDK [Internet]. National Institute of Diabetes and Digestive and Kidney Diseases. [cited 2018 Aug 2]
2. Low Blood Glucose (Hypoglycemia) | NIDDK [Internet]. National Institute of Diabetes and Digestive and Kidney Diseases. [cited 2018 Aug 2]