(USMLE topics) What is A1C? A1C as a tool for managing diabetes, factors that affect A1C accuracy.

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A1C test is a blood test used to diagnose diabetes and monitor the progress of a treatment plan. The test result reflects the average blood sugar levels in the past 3 months.
A1C is a type of glycated hemoglobin – a hemoglobin that is bound to glucose. Hemoglobin is the major protein of red blood cells. A1C forms as a result of interaction between red blood cells and sugar in the blood. The higher the blood glucose levels, the more glucose binds to hemoglobin, the greater the amount of A1C. The A1C blood test reports the percentage of hemoglobin that is bound to glucose.
Once a hemoglobin is glycated, it remains that way in the blood, until the red blood cell carrying it is removed from the circulation. Because the average lifespan of a red blood cell is 3 to 4 months, A1C measurement represents the status of blood glucose for the past 3 months or so.
A normal blood glucose level corresponds to an A1C result of less than 5.7%. An A1C level higher than 6.5% indicates diabetes. Between 5.7 and 6.5% is prediabetes.
An estimated average glucose level, eAG, measured in concentration units, milligrams per deciliter or millimoles per liter, can be calculated and often reported in addition to the A1C percentage. eAG helps patients link A1C to the numbers they obtain at home using a blood sugar measuring device.
A1C is an important tool for managing diabetes. For most diabetics, the goal is to bring A1C level down to 7% or less. However, patient’s age and other health conditions must be taken into account when setting goals. In general, younger patients who don’t often experience severe low glucose, known as hypoglycemia, need lower goals to avoid diabetes complications in the many years ahead. Older patients or those having frequent low-glucose episodes, may have a higher goal.
It is important to note that several factors can affect the accuracy of A1C test result, in which case, unless corrections can be made, A1C cannot be used to assess blood glucose levels. For example, people with blood disorders such as sickle cell disease, thalassemia, or hemolytic anemia may have a lower than expected A1C because their red blood cells have a shorter lifespan. Iron deficiency anemia, on the other hand, is associated with increased red blood cell lifespan and falsely high A1C measurements. Some people of African, Mediterranean, or Southeast Asian descent may have uncommon forms of hemoglobin that produce falsely high or low results. Certain kidney and liver diseases may affect the turnover rate of red blood cells and give rise to inaccurate A1C readings. Finally, recent blood loss or transfusion will also skew the test results.

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In this video I discuss what is blood sugar level, and what causes high and low blood sugar levels. We also look at insulin’s role in blood sugar levels, and some of the risk factors for developing type 2 diabetes.

Transcript (partial)

In this video we are going to discuss what blood sugar or blood glucose is, and why it is important.

Blood sugar level is the amount of glucose(sugar) present in the blood. Our body gets glucose from some of the foods we eat.

After the digestive process, the liver releases glucose into the bloodstream, sending it to cells to be used as energy. As glucose is released into the bloodstream, blood sugar levels rise. This triggers the pancreas to release the hormone insulin, which tells the cells to open up and let the glucose in, which lowers blood sugar levels.

Excess glucose is stored as glycogen in the muscles and liver. This process happens many times throughout the day after we eat.
A normal fasting (no food for 8 hours) blood sugar level is between 70 and 99mg/dl, and a normal level two hours after eating is less than 140mg/dl.

So, why is this important? Well, there are 3 main reasons we need to be aware of our blood sugar level.

The 1st reason is that high blood sugar levels can lead to type 2 diabetes. Type 2 diabetes is when the body doesn’t use insulin properly (insulin resistance), or when the pancreas stops producing enough insulin. Over time, High blood sugar levels can put a lot of stress on the pancreas, possibly causing it to become permanently damaged. 95% of all diabetes cases in the US are type 2.

Researchers don’t fully understand why some people develop type 2 diabetes and others don’t. However, there are some factors that increase the risk.

-being overweight – the more fatty tissue you have, the more resistant your cells become to insulin.

-fat distribution – more fat storage in the abdomen increases the risk

-inactivity – Physical activity helps you control your weight, uses up glucose as energy and makes your cells more sensitive to insulin.

The 2nd reason we need to monitor our blood sugar levels is that High levels can also lead to atherosclerosis, which is hardening and narrowing of the arteries. This can block the arteries, putting blood flow at risk, which can lead to other problems.

The 3rd reason is low blood sugar levels, this is rare in non-diabetics. This can be caused by certain medications, excessive alcohol consumption, excessive exercise, and from meals high in refined carbs.

Timestamps
0:00 Intro
0:15 What is blood sugar level?
0:30 Example of sugar travelling in the bloodstream
1:38 Normal blood sugar level
1:57 What is type 2 diabetes?
2:34 Risk factors for type 2 diabetes
2:55 Blood sugar and Atherosclerosis
3:14 Low blood sugar levels
3:28 Recommendations

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