Blood Glucose 101: Blood Sugar Basics

Blood Glucose 101: Blood Sugar Basics

Blood Glucose 101: Blood Sugar Basics Is Coauthored by:  Rakesh Patel, D.O. Board Certified Endocrinologist


If you are like most people, you probably don’t give much thought to your blood glucose levels until something goes wrong. And when it does go wrong, it can be stressful to become a glucose expert overnight.

We know it’s hard to process the idea that you are experiencing high blood sugar or diabetes. So let’s review the basics of blood sugar – otherwise known as Glucose 101.

What is blood glucose?

Blood glucose, also known as blood sugar, is the amount of sugar in your blood at any given time. Glucose is the primary type of sugar in our food and the main energy source for our cells. Our bodies run on glucose, and our pancreas regulates blood glucose fluctuations within a specific range so that our cells can function correctly. When blood glucose levels are too low, we feel tired, which affects our mood, concentration, and productivity. Our brain functions such as thinking, memory, and learning are closely linked to glucose levels and how efficiently the brain uses this fuel source. Suppose there isn’t enough glucose in the brain, for example. In that case, neurotransmitters, the brain’s chemical messengers, are not produced, and communication between neurons breaks down.

When blood glucose levels are too high, it can damage our organs and cause other serious health problems. High sugar can crystallize in the blood. Sugar crystals are very sticky, and they tend to attach to cells and block arteries by building up in blood vessels and other organs.

How does the body process glucose?

Did you know that glucose metabolism begins before a person takes their first bite? When we smell or even anticipate food, our parasympathetic nervous system is activated and begins secreting digestive juices. Then, when we take our first bite, our body recognizes the food as foreign and begins the process of digestion.

During the digestive process, enzymes in the gut break down carbohydrates into smaller molecules, including glucose. Once these molecules are small enough, they are absorbed through the intestinal wall and bloodstream.

From there, insulin is secreted to help shuttle glucose through the bloodstream to muscle cells, where it can be stored as glycogen or used for energy. But what happens when we eat more glucose than our cells can use?

This is where things get a little tricky. When blood sugar rises too high, it becomes toxic to the body. In response, the pancreas secretes insulin to try and remove the excess glucose from the bloodstream.

But sometimes, the pancreas can’t keep up. This is when blood sugar levels become too high, and diabetes develops.

What happens to my glucose levels when I eat sugar or carbohydrates?

If you eat a meal high in sugar or carbohydrates, your blood sugar level will rise more than if you had eaten a low-sugar or low-carbohydrate meal. If you have diabetes, it is crucial to watch your carbohydrate intake to better control your blood sugar levels.

What happens to my glucose when I don’t eat?

If you don’t eat, your blood sugar levels can become too low, which is called hypoglycemia. This can cause you to feel tired, have a headache, or be confused. If your blood sugar levels get too low, you may need to eat or drink something with sugar to raise your blood sugar level.

Early symptoms of hypoglycemia (low blood sugar) may include:

Dizziness; feeling shaky or sweaty; hunger; a fast, pounding heartbeat; inability to think clearly and confused; feeling irritated or moody; anxiousness; or headache.

Hypoglycemia in people with type 1 diabetes or type 2 diabetics who use insulin can be even more dangerous. They may experience severe or even nocturnal (nighttime) hypoglycemia.

Nighttime hypoglycemia is characterized by:

  • Bad dreams/nightmares
  • Wet clothing or bedsheets due to sweat
  • Exhaustion upon waking up; feeling of confusion.

Board-certified endocrinologist Dr. Rakesh Patel warns his patients to watch for nocturnal low blood sugar. “A nocturnal hypoglycemic event is the single most dangerous event for a patient that has diabetes. Unless we monitor blood glucose while a patient sleeps, they may not realize it happened.”

How does diabetes affect glucose metabolism?

People with diabetes have trouble metabolizing glucose. This means that their bodies cannot use glucose for energy the way they should. When you have diabetes, your pancreas doesn’t make enough insulin, or your body can’t use insulin properly. Insulin is a hormone that helps your body to control blood sugar levels.

People who are prediabetic or diabetic (usually type 2) also have insulin resistance. Insulin resistance makes the cells of the body respond abnormally to insulin. Because of this disfunction, sugar cannot enter the cells as it should. This results in high blood sugar levels despite the body producing more and more insulin to correct the high glucose.

Dr. Patel tries to make insulin resistance easy for his patients to understand. “How I explain insulin resistance to my patients is to imagine that insulin is like a party guest knocking on the door. But insulin resistance is like loud music. It makes the host(cell within the body) unable to hear the knock at the door. Eventually, when enough party guests arrive (insulin) and make enough noise, the host(cell) finally hears the knocks. The guests enter, and all the gifts (sugar) they bring can now be enjoyed. This explains why an insulin-resistant patient produces more insulin than is typical of type 1 or non-diabetics but can still have high blood sugar.”


What is a blood glucose test?

A blood glucose test is a screening tool for diabetes.  It measures the level of glucose (sugar) in a patient’s blood. One blood glucose test is a Hemoglobin A1c (HbA1c) test. HbA1c is a lab test to measure how much sugar is bound to your red blood cells (hemoglobin).

Healthcare providers use other types of blood sugar tests to measure the level of glucose in the blood. One measure is called fasting blood sugar (FBS). It is usually done in the morning after fasting between 8-12 hours.

A glucose challenge test involves a patient first drinking a sugar-sweetened drink. Then a patient has their blood sugar checked an hour later to see how well the body handled that sugar load. If your blood sugar is high, you may be ordered to take a follow-up test called the oral glucose tolerance test (OGTT).

Some patients, especially pregnant women, may do a glucose tolerance test. With this test, a patient will be given a special drink that contains a high amount of glucose. The patient’s blood will be drawn before and an hour after taking the drink to see how well the body handled that sugar and its efficiency in moving it into the muscle tissue. The test for pregnant women is similar but maybe done differently.

What is the range of normal for blood glucose levels?

The normal blood glucose range is 70-100 mg/dL before meals (fasting) and less than 140 mg/dL two hours after meals. If your fasting blood glucose is higher than 100 mg/dL, or your blood glucose is higher than 140 mg/dL two hours after meals, you may have diabetes.

What is an HbA1c (A1c)?

The HbA1c test measures your average blood sugar level over the past three to six months. The test shows how well your body processes sugar.  It also reveals if your diabetes management plan controls your blood sugar effectively. The HbA1c test is also called the glycated hemoglobin or glycosylated hemoglobin test. It measures how much of the surface area of your red blood cells have been covered by crystallized sugar.

Sugar is a sticky substance, and high amounts of sugar in the blood will create sugar crystals with sharp edges and are very syrupy.

Red blood cells, which have a lifespan of approximately three to six months, can bind together and be coated by these sugar crystals. The more sugar you have in your blood, the more coating on the red blood cells. Too many sugar-coated red blood cells can bind together and clog your arteries. This blocks blood flow to vital organs and tissues such as the retina and causes damage to the body.

The A1c test is an excellent way to see how well your diabetes treatment plan works over time. It is essential to talk to your healthcare provider about what your A1c results mean. Then you work together to determine what your future A1c goals should be.

What to know about HbA1c?

It is significant to point out that HbA1c was one of the first tests developed to measure treatment efficacy and glucose management. The American Diabetes Association (ADA) recommends that patients have a goal of an A1c under 7. But Dr. Patel says, “The A1c goal for most of my patients is under 7, but sometimes it’s 6.5. It’s unique to the patient”.

Your HbA1c is an average metric of how well you have managed your sugar levels in the past three to six months. Like other average metrics, an HbA1c of 7 can have 3 different meanings.

This is why it is necessary to measure your glucose continuously for some time to see changes in your blood glucose. This helps your provider decipher what your daily glucose can actually look like.

Today, many endocrinologists believe that “Time In Range” is a much better indicator of how well a patient manages their diabetes.

“We have patients come to the office every three months because the A1c is a three-month average. What will we do when we have software and time in range for 24 hours a day? We will have to practice differently. We will need to see some patients more frequently and others less frequently. Not just one month earlier or later, but in terms of days. The insulin changes that we make have an immediate effect on sugars. Why do we wait 3 months or even one month to see progress?” says Dr. Rakesh Patel, D.O.

What is a blood glucose monitor?

A blood glucose monitor (blood glucose meter) is an over-the-counter (OTC) device that you can use to test your blood sugar (glucose) levels at home.

Glucose meters require a finger prick by a lancet. This draws a drop of blood that you place on a disposable test strip and place into the monitor. The monitor displays a blood sugar level in units of mg/dL (U.S.) or mmol/L (international). Blood glucose monitors are relatively easy to use and give you results within seconds. The main issue with using glucose meters is fingersticks and lancets. Lancets are tiny needles that you use to prick your finger and obtain a small blood sample from your finger. To use a meter, you will have to use a lancet each time you test to prick your finger to get a drop of blood. Many patients find this method inconvenient, but it is generally affordable.

Why should I use a Continuous Glucose Monitor (CGM) instead of a meter?

To effectively measure your blood glucose, you need to check your sugar levels at least 3-6 times per day. After a few times, your body will respond by forming calluses, and your fingertips will harden in response. This makes the finger pricks more challenging and more painful.

Sometimes a doctor will order a device that constantly measures a patient’s blood glucose levels called a Continuous Glucose Monitor (CGM). A CGM consists of a sensor inserted below the skin, usually on the abdomen. The sensor is attached to a transmitter that sends data wirelessly to a display device. The display device shows the patient’s blood glucose levels in real-time and stores data for later review.

A CGM can be very useful for type 1 and type 2 diabetics. It can help people with type I diabetes by identifying patterns and trends in blood glucose levels that may be difficult to see from finger sticks alone. It can also help people with type II diabetes by providing motivation to make lifestyle changes and improve glycemic control.

Dr. Rakesh Patel prefers that all his patients be on a CGM. “One of the biggest issues in diabetes is that patients are overwhelmed with things to do, medications to take. With CGM, a big burden is lifted.”

If you are interested in learning more about CGMs, please speak with your healthcare provider.