Dr Aidin Rawshani

How to measure blood sugar (glucose, blood glucose)

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How to measure blood sugar and what is HbA1c

Measuring blood sugar (glucose in the blood)

Blood sugar can be measured in several ways. In clinical practice, the concentration of sugar (glucose) in the plasma is usually controlled, which is called plasma-glucose (or P-glucose). To be diagnosed with diabetes, fasting P-glucose should be ≥ 7.0 mmol/L An abnormally high P-glucose (≥ 7.0 mmol/L) must be confirmed with a further sampling.

Several other clinics and especially hospitals also measure long-term blood sugar levels (Hemoglobin A1c, HbA1c) to diagnose and control diabetes, this blood test may only be used for diagnosis of type 2 diabetes in adults. HbA1c reflects the mean blood sugar levels in the last 2-3 months and HbA1c levels exceeding ≥ 48 mmol/mol are used as a limit value to establish the diagnosis of type 2 diabetes.

The World Health Organization (WHO) states that HbA1c levels between 42-47 mmol/mol indicate the “pre-diabetes” state, and the American Diabetes Society (ADA) believes that HbA1c between 39-47 mmol/mol is a sign of “pre-diabetes”. There are also clinics investigating blood sugar metabolism using a test called Oral Glucose Load (OGTT) where levels above ≥ 12.2 mmol/l indicate that the individual suffers from diabetes.

In diabetes, the treatment of blood sugar levels is controlled and patients are regularly followed to check blood sugar. Research studies show that the risk of complications in diabetes is reduced by more than 3% for each 1 mmol/mol decrease in HbA1c, regardless of what level the decrease occurs.

The body regulates blood sugar levels tightly as part of metabolic homeostasis and in people with diabetes there are several factors that cause impaired blood sugar metabolism and increased blood sugar levels despite ongoing treatment against this. We humans usually have 4-6 grams of glucose in the blood constant.

Glucose is a sugar stored in the liver or skeletal muscles in the form of larger molecules called glycogen; in fasting people the blood sugar concentration is maintained at a constant level by splitting glycogen stores to produce sugar.

Glucose is the main source of energy for humans and is critical for many normal functions in a number of tissues, especially for the brain. There are different kinds of sugars and the one that our body uses most is called glucose, other sugars that we eat are fructose from fruit or lactose from milk, which is converted into glucose in our bodies.

Our body usually even breaks down starch to extract glucose. Glucose is absorbed from various sources such as the intestines, liver and musculature, uptake is partly regulated by the hormone insulin secreted from the pancreas.

Blood sugar levels are usually lowest in the morning, before the first meal of the day and rise after eating food or drink. Elevated blood sugar is an indicator of a pathological condition, most often diabetes. Continued high blood sugar levels are called hyperglycaemia and low levels are called hypoglycaemia. When the body’s blood sugar levels are low, pancreatic release the hormone glucagon which in turn stimulates the liver to secrete the stored sugar, glucagon also stimulates the liver to produce more sugar. When blood sugar levels then rise, the release of pancreatic glucagon decreases to stabilize blood sugar levels.

The figure illustrates the pancrease. In the organ there are small islets called the islets of Langerhans where a particular type of cells called beta cells produces and secretes the hormone insulin that is so important for the body. Insulin ensures that glucose is absorbed from the bloodstream into the body’s various cells. Source: Smart Servier Medical Art
A cross sectional view of the pancreas were islet of langerhans can be seen.

What is HbA1c?

Hemoglobin A1c (HbA1c) or glycaemic haemoglobin is a measure of average blood sugar in the last 2-3 months. In the red blood cells there is hemoglobin that binds to the oxygen, which can then be transported from the lungs to all tissues of the body. When the haemoglobin hits glucose, the sugar binds to the haemoglobin, it is said that haemoglobin has been “glycosylated” and it is called HbA1c. The red blood cells are formed in the bone marrow and break down after about 120 days of constant circulation in the body.

What is measured in HbA1c sampling is the proportion (either as a percentage or per mille) of glycolised haemoglobin. HbA1c thus indicates the proportion of haemoglobin, as a percentage or per mille, that has glucose bound to it. If you have high blood sugar levels in the blood, a greater proportion of the haemoglobin will be glycolised and HbA1c levels will be higher. Blood glucose levels over the past 30 days determine 50% of the value of HbA1c.

In the clinic, the number of annual controls of HbA1c should be adjusted for each individual, it is recommended that HbA1c be checked between 2-4 times a year.

There are quite a few sources of error in measuring HbA1c that one should be aware of, usually falsely low HbA1c values, i.e. that the individual actually has higher levels. Several blood diseases leading to malformed constituents of proteins in the blood and different blood cells affect HbA1c levels.

Recommendations for HbA1c according to the Swedish Association for Diabetology
Diabetes typeOptimal controlAcceptable levelsUnsatisfactory levels
Type 1 diabetes≤ 52  52-62≥ 62
Type 2 diabetes≤ 4242-52≥ 62

The relationship between HbA1c and small vessel disease (microvascular complications) is well affected, the levels of small vascular disease of the fundus (retinopathy) are already seen at HbA1c 48 mmol/mol in individuals with type 1 diabetes. HbA1c less than 48 mmol/mol is recommended to reduce the risk of severe eye, kidney and nerve damage, fasting plasma glucose should be less than 6-8 mmol/l and less than 10 mmol/l during the daytime.

The risk of complications is further reduced if one does not smoke and at the same time has a good blood pressure.

Some individuals have swinging blood sugar that is difficult to regulate and causes frequent sensations and recoil in blood sugar levels as blood sugar usually rises rapidly if it becomes too low. Achieving an HbA1c below 60 mmol/mol for an individual with type 1 diabetes requires a well-structured life with frequent blood glucose measurements, knowledge of the disease and treatment.

Glycolized hemoglobin (HbA1c)Plasma-Glucose
406-7
507-9
609-10
7010-12
8012-13
9013-15
10015-17
11016-18
12017-20

Diabetic complications and HbA1c

In Sweden, several population studies have been conducted to investigate the relationship between HbA1c and macrovascular complications. {TanCredi:2015BC, Lind:2011ct, Lind:2014dd} In these studies, it has been observed that even at normal blood sugar levels, i. e. HbA1c 53 mmol/mol for individuals with type 1 diabetes and type 2 diabetes, so there is an increased risk of cardiovascular complications and premature death compared to the general population. These epidemiological studies show that normal blood sugar levels continue to increase 2-4 times the risk of complications.

Individuals with diabetes appear to be at the highest risk of developing heart failure compared to individuals without diabetes. However, these studies always show that people with diabetes and low or normal HbA1c levels have a lower risk of cardiovascular disease and death.

The risk increases further if the person has high blood pressure, high blood lipids or smokes.

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