Dr Aidin Rawshani

All about blood sugar (glucose) and HbA1c


Blood sugar, HbA1c and glucose meter

What is blood sugar, glucose and blood glucose?

Dear child has many names, and so has sugar. In the human body, it is glucose we call sugar. Glucose is a sugar species and it is the only sugars that the cells of the body can use to produce energy. When we say blood sugar, blood glucose, or sugar in the blood, we mean the concentration of glucose in the blood. The concentration is most often indicated by the unit mmol/L (millimol/liter). All people with diabetes have abnormally high blood sugar, which is the very definition of diabetes. Read more about type 1 diabetes, type 2 diabetes in separate chapters.

Everyone with diabetes has high blood sugar

In diabetes, it is important to treat the high blood sugar to reduce the risk of future complications. This is achieved primarily through improved diets, increased physical activity and adherence to drug therapy. The medicines available are either insulin or various tablets.

The higher the blood sugar you have, the greater the risk of complications (sequelae) to diabetes. High blood sugar mainly increases the risk of kidney disease (nephropathy), damage to the retina (retinopathy, leads to impaired vision), and damage to nerve pathways (neuropathy). High blood sugar also increases the risk of serious cardiovascular diseases. Read more about complications of diabetes here.

Why is good blood sugar levels important?

It is important that you control your blood sugar levels as well as you can because high sugar levels over long periods increase the risk of diabetic complications.

How to measure blood sugar (glucose)

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. Abnormally high P-glucose (≥ 7.0 mmol/L) must be confirmed by another 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 pancreatic disease. 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: See image: SMART Servier medical art

Recommended blood sugar levels

The recommended blood sugar levels are listed below for adults with type 1 diabetes, type 2 diabetes and children with type 1 diabetes.

The table provides general guidance. An individual goal set by your healthcare team is what you should strive for.

Recommended levels from the organization NICE

Type of diabetesIn the morningBefore meals (pre-prandial)Approximately 90 minutes after meals (post-prandial)
Non -diabetic4.0 to 5.9 mmol/l< 7.8 mmol/l
Type 2 diabetes4 to 7 mmol/l< 8.5 mmol/l
Type 1 diabetes5 – 7 mmol/l4 to 7 mmol/l5 to 9 mmol/l
Children with type 1 diabetes4 – 7 mmol/l4 to 7 mmol/l5 to 9 mmol/l

*Figures for non-diabetics are provided for information but are not included in Nice guidelines.

Normal blood sugar in diabetes mellitus

Normal blood sugar levels

Blood glucose values should be within a normal range (48 mmol/mol) in order for people with diabetes to minimize the risk of future complications.

This chapter describes what normal blood sugar levels are among adults and children with type 1 diabetes and type 2 diabetes.

Individuals with diabetes who measure blood sugar daily at home need to know how they interpret sugar levels to adjust meals, activities and medicines.

It is difficult to specify normal or optimal blood sugar levels for all people because target values need to be adapted for each individual. People without diabetes have long-term blood sugar (HbA1c) 42 mmol/mol, despite this, it is believed that optimal levels for people with diabetes are HbA1c 48 mmol/mol.

For most healthy individuals, normal blood sugar levels are as follows:

  • Between 4.0 to 5.4 mmol/l (72 to 99 mg/dl) on fasting
  • Up to 7.8 mmol/l (140 mg/dl) 2 hours after eating

For people with diabetes, target blood sugar values are as follows:

  • Before meals: 4 to 7 mmol/l for people with type 1 or type 2 diabetes
  • After meals: below 9 mmol/l for people with type 1 diabetes and below 8.5 mmol/l for people with type 2 diabetes

Blood sugar levels in the diagnosis of diabetesThe following table contains criteria for diagnosing diabetes and prediabetes.

Blood sugar levels in diabetes and prediabetes

Random measure< 11.1 mmol/l> 11.1 mmol/l
Fasting< 5.5 mmol/l5.5 – 6.9 mmol/l> 7.0 mmol/l or
2h after meal< 7.8 mmol/l7.8 – 11.0 mmol/l> 11.1 mmol/l

Fasting glucose in the blood

A fasting plasma glucose sample is taken after at least eight hours of fasting and is therefore usually taken in the morning.

In NICE guidelines, fasting plasma glucose of 5.5 to 6.9 mmol/l is considered to be at greater risk of developing type 2 diabetes, especially when accompanied by other risk factors for type 2 diabetes.

Oral Glucose Tolerance Test (OGTT)

An oral glucose tolerance test involves taking a fasting sample of blood and then drinking a very sweet drink containing 75 g of glucose.

After drinking this drink, you need to rest until further blood tests are taken after 2 hours.

When to measure blood sugar?

It is good to check blood glucose values at regular intervals. The number of times per day that the blood sugar level should be measured depends entirely on the individual and the type of diabetes. People with type 1 diabetes who use insulin should check blood glucose levels before each meal, sometimes as often as five times a day.

För personer med typ 2 diabetes som behandlar sitt sjukdomstillstånd med enbart kost, bör testa sina sockernivåer flera gånger i veckan.

Are there special times when blood sugar should be measured?

Every time you feel unwell, and when you may feel your blood sugar is getting too low or too high, you should check your blood sugar levels.

People with diabetes who have significantly elevated blood sugar levels (20 mmol/l) should also control the content of ketones in the urine.

What is an HbA1C test and how does it reflect blood glucose?

HbA1c tests show average blood sugar levels over a longer period of time. HbA1c is called glycosylated hemoglobin in medical language and more of it is produced in the body by high blood sugar levels. Increasing HbA1C levels indicates a greater risk of complications.

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.

Glycemic hemoglobin (HbA1c)Plasma-Glucose

What are good blood sugar levels?

Health Organization NICE recommended the following

  • A normal pre-prandial (before meals) blood glucose level is between 4 and 7 mmol/l.
  • After eating (post-prandial), the levels should be below 9 mmol/l when tested 2 hours after a meal.
  • When going to bed for the night, the levels should not be more than 8 mmol/l.

HbA1c for the diagnosis of diabetes

An HbA1c test does not measure blood glucose levels directly, but the result of the test is influenced by how high or low blood sugar levels have been in the last 2 to 3 months.

HbA1c in diabetes or prediabetes

  • Normal: below 42 mmol/mol
  • Prediabetes: 42 to 47 mmol/mol
  • Diabetes: 48 mmol/mol

Macrovascular 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.

Diabetes diary

Individuals with diabetes who regularly check their blood sugar levels should use a diabetes diary to monitor blood sugar trends and detect patterns in everyday life that may be associated with blood sugar fluctuations. The Diabetes Diary allows you to keep track of factors such as diet and exercise and how this affects your blood sugar by recording your diet, exercise and blood sugar values in the personal diary. In addition, this facilitates the follow-up visits with the diabetes nurse by going through the Diabetes Diary together. After that, it is possible to take measures to correct what causes blood sugar fluctuations.

Check your blood sugar before and after meals (either 1 to 4 hours before or after), this will help you see how well you and your medicine handle different meals. Note the meals that make blood sugar difficult to control and see if blood sugar levels are high during certain parts of the day. Watch how exercise, illness and stress affect your blood sugar levels and dosage doses. For individuals who record blood glucose values over a number of years, it is possible to see seasonal trends. Diabetes diaries are available to download free of charge.

Recommended glucose levels from the National Institute for Clinical Excellence (NICE) for individuals with and without diabetes are listed below.

Recommended blood sugar levels according to NICE
DiagnosisIn the morningBefore meals90 min after meals
Non-diabetic   4.0 – 5.9 mmol/L< 7.8 mmol/L
Type 1 diabetes5.0 – 7.0 mmol/L4.0 – 7.0 mmol/L5.0 – 9.0 mmol/L
Type 2 diabetes 4.0 – 7.0 mmol/L< 8.5 mmol/L
Minors with type 1 diabetes4.0 – 7.0 mmol/L4.0 – 7.0 mmol/L5.0 – 9.0 mmol/L
Diagnosis criteria for diabetes, impaired glucose tolerance and elevated fasting blood sugar
Random   4.0 – 5.9 mmol/L< 7.8 mmol/L
Fasting 4.0 – 7.0 mmol/L< 8.5 mmol/L
2 – h after meals5.0 – 7.0 mmol/L4.0 – 7.0 mmol/L5.0 – 9.0 mmol/L
Minors with type 1 diabetes4.0 – 7.0 mmol/L4.0 – 7.0 mmol/L5.0 – 9.0 mmol/L

Blood glucose meters

The management of diabetes has become easier with the improvement of technology. Today, several patients use continuous blood glucose meters at home to constantly control blood sugar levels. The technology provides an opportunity to create diagrams of one’s own blood sugar trends, save dates for certain blood sugar values, insulin doses and the amount of training.

The majority of individuals with diabetes measure blood sugar levels through a normal blood glucose meter where you stick on a part of the body, usually your fingertips and record the sugar content in a drop of blood. A low value (P-glucose 3 mmol/L) should always be addressed. In certain conditions, blood sugar should be monitored more frequently, for example in infections, associated with heavy physical exertion, long trips, concomitant corticosteroids therapy and long driving.

Patients with type 2 diabetes and only tablet therapy treated with either Metformin, Glitazones, GLP-1 analogues, DPP4 inhibitors and SGLT-2 inhibitors do not need to monitor blood sugar daily as the risk of blood sugar falls (hypoglycaemia) is very rare. In elderly individuals with diabetes, the aim is not to reduce the risk of cardiovascular complications without reducing the risk of acute complications such as diabetes ketoacidosis or hypoglycemia, therefore it is more accepted that older individuals have higher blood sugar levels.

Margin of error in blood glucose measurement
Plasma-glucoseLower limitUpper limit

The precision of blood glucose meters can be influenced by several factors, and people with diabetes who regularly check their blood glucose values should know the upper and lower limits to estimate where their actual blood glucose levels are. The temperature can affect these machines that work best at room temperature. Your healthcare professional may then use this information to improve your treatment, for example, by informing about food choices and amounts of food, helping to make drug dosage decisions, and identifying periods of high and low blood glucose levels.

All people who use insulin for the treatment of type 1 diabetes and type 2 diabetes should regularly monitor their blood sugar levels. Some people who use medicines from the drug group Sulfonylurea, should also test their blood sugar levels to identify periods of low blood sugar levels because the drug is associated with blood sugar drops.

Individuals with diabetes have different attitudes when it comes to controlling blood sugar. Many people believe that regular checks on blood sugar are not helpful and only contribute to anxiety. However, several others, especially those who are aware of how to interpret the results and take appropriate measures, are interested in regularly monitoring their blood sugar levels to optimise their diabetes treatment.

People with type 1 diabetes should test their blood sugar levels at least 4 times a day, including before each meal and before going to bed, some people with type 1 diabetes check their blood sugar levels about 10 times daily. In the Västra Götaland region, the cost of 10 blood glucose measurements per day is estimated to be around 10,000kr per year. People with type 2 diabetes not treated with insulin usually do not have access to blood glucose meters at home but there is evidence that structured monitoring of blood sugar levels in type 2 diabetes is beneficial and may improve their diabetes control.

Blood glucose measurement is a major part of diabetes treatment for people with diabetes and regular test sites on the body can become painful over time, therefore experts have identified alternative test sites. The fingertips are traditionally used for blood sugar tests because they have many capillaries (small vessels), but the fingertips have many nerve endings and are therefore sensitive. Alternative test sites are the palm, the upper part of the forearm, abdomen and thigh. Not all blood glucose monitors can measure blood glucose levels from all of these body locations, but fingertips, abdomen and thigh tend to work for most blood glucose meters.

Continuous glucose monitoring (CGM)

Blood glucose meters in the home have been a big step forward for diabetics. More recently, continuous glucose monitoring has been developed which no longer means the unpleasant sticking at the fingertips and blood sugar levels are continuously recorded. When Continous Glucose Monitoring (CGM) measure your blood sugar levels, this is recorded in a management system that can store an enormous amount of data, it is possible to check the dates of different blood sugar levels and how these relate to insulin doses or the amount of training. With increased access to networks, it is possible that individuals with diabetes can transmit data on their blood sugar levels to their doctor. Your healthcare professional can then use this information to improve your treatment.

Several different factors such as hobbies, activities and personal preferences can influence one’s choice of choosing a continuous blood glucose meter. A blood glucose meter uses blood to measure sugar levels while a continuous glucose meter is placed in the body but not in the bloodstream; the sensors of a continuous glucose meter measure the glucose in the interstitial fluid, i.e. the fluid in and around the body’s cells.

These devices involve less invasive techniques for measuring glucose. The relationship between blood sugar levels and sugar levels in the interstitial fluid is carefully studied but values in the blood reflect levels in the interstitial fluid well. Seeing blood sugar levels in real time can help the individual make more informed decisions about how to balance their diet, physical activity and medicines.

A continuous glucose meter (CGM) that measures the sugar levels in the interstitial fluid and not directly in the bloodstream.

One advantage of continuous glucose monitoring is that the device always records glucose levels, regardless of whether the person is showering, working, exercising or sleeping. The device can sound an alarm when the glucose level is too low or too high. It is possible to record the time you eat, while exercising or taking your medications. However, the apparatus needs to be checked twice daily. It is necessary to knit oneself some time daily to calibrate the appliance and the sensor additionally needs to be replaced after 3-7 days depending on the model. Individuals with type 1 diabetes and intensive insulin therapy, poor diabetes control or inability to feel a fall in blood sugar should consider continuous glucose monitoring.

Continuous Glucose Meter (CGM) Source: Image from Medtronic Diabetes Image database.

Diabetes complications

  • Kidney Disease
  • Nerve injury
  • Disease of the retina
  • Heart disease
  • Stroke

This list of diabetes complications may look frightening, but the main thing to remember is that the risk of these problems can be minimized by good blood sugar control.

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