Diagnosing diabetes

- [Voiceover] Let's discuss the presentation and diagnosis of diabetes mellitus. Recall that diabetes mellitus is a group of disorders that can be caused by multiple different underlying mechanisms. However, all the different types are diagnosed in the same way, and that is a combination of clinical presentation and diagnostic tests. So let's erase this here and start with the presentation of diabetes mellitus. Recall there are two types of diabetes, type I and type II, and depending on the type the disease presentation will differ. And there are three main ways in which someone with diabetes will present before they're diagnosed with the disease, and they are acute, subacute, and asymptomatic. Now let's start with the acute presentation. This is the most severe presenting situation and can be life threatening for both type I and type II diabetes. This individual becomes very sick over a relatively short period of time, usually only a couple of days. Now symptoms will include things like nausea, vomiting, and abdominal pain and this often results in severe dehydration, and as such the individual may even become confused or unconscious as a result. In type I diabetes, this is known as diabetic ketoacidosis, or DKA for short. And it is how about 30% of individuals with type I diabetes will initially present before diagnosis. In type II diabetes, the acute presentation has a much longer name. It's known as hyperosmolar nonketotic state, or HHNS for short, and it's much less common than DKA as it's the initial presentation for only about 2% of individuals with type II diabetes. Now the difference between DKA and HHNS has to do with the difference between the underlying mechanisms of type I diabetes and type II diabetes. Now the most important difference is that in DKA the individual will become acidotic due to the production of ketoacids, hence the name diabetic ketoacidosis as opposed to hyperosmolar nonketotic state where ketoacids are not produced. Now the next way individuals with diabetes can present is what we'll call subacute. And this is a mild to moderate presentation that occurs over a period of weeks to months. And these individuals or maybe someone close to them notice that they are generally just not feeling as well as they normally do and they may experience symptoms of fatigue, increased thirst, frequent urination, or even weight loss. Now, once again this can occur with either type I or type II diabetes. And in type I diabetes, this is the most common form of presentation before diagnosis, accounting for about 70% of individuals with type I diabetes. In type II diabetes, this is also common, however the predominant symptoms are a little bit more vague and weight loss is less common. Then the last way individuals with diabetes can present is through asymptomatic screening tests. So type II diabetes affects nearly 10% of the population, and due to this high prevalence, potentially severe complications, and the relative ease of treatment, most adults, especially those with the risk factors of type II diabetes should be routinely screened for the disease. And this is the most common means by which type II diabetes is diagnosed. However, it's rare for the diagnosis of type I diabetes as routine screening for type I diabetes is not usually performed. So let's move on to the diagnostic tests for diabetes mellitus Regardless of the type of diabetes or the severity of presentation, laboratory tests are necessary for the diagnosis of diabetes mellitus. So let's briefly review the general mechanism of diabetes to gain a better understanding of the two major laboratory tests that are used to diagnose the disease. As the blood glucose levels in the body rise, this is sensed by the beta cells in the pancreas which secrete the hormone insulin. And insulin then acts on cells throughout the body to take the glucose from the blood up and thus lower the blood glucose levels. So in diabetes mellitus, regardless of the type, this insulin pathway is not working properly, therefore the body is not able to lower blood glucose levels. And this results in increased blood glucose levels known as hyperglycemia, which is the characteristic finding of diabetes mellitus. Now a side effect of hyperglycemia is a proccess known as glycosylation, which is the non-enzymatic attachment of glucose to proteins. And one protein that this occurs with that is of importance in diabetes mellitus is the protein hemoglobin which is located within red blood cells. And in the presence of hyperglycemia, glucose will attach itself to an abnormally high percentage of hemoglobin within the red blood cells. And this is known as glycosylated hemoglobin, or hemoglobin A1C, and it's the hyperglycemia and the hemoglobin A1C that are tested for in the blood to aid in the diagnosis of diabetes mellitus. So let's put this diagram over here to the side and discuss a little bit more about these diagnostic tests. First, let's talk about the three categories of results for the diagnostic tests. And the first is a normal level. The second is the level that's associated with diabetes. And then in between is a third category, and it relates only to type II diabetes, and it's known as pre-diabetes. Since type II diabetes is a chronic disease that typically takes many years to develop and it's routinely screened for, often times individuals will have a test result that is above the normal level however not severe enough to be considered diabetes and this is known as pre-diabetes. And it's important because individuals with pre-diabetes, as it's name suggests, are much more likely to develop type II diabetes in the future. So by identifying them as having pre-diabetes, they can start treating the underlying mechanism through lifestyle modifications such as weight loss, proper diet, and routine exercise in order to prevent or delay the development of type II diabetes in the future. Now, as we mentioned before, there are two major types of laboratory tests used to diagnose diabetes mellitus, and they are blood glucose levels and hemoglobin A1C. The blood glucose level can be measured by many different methods and, unfortunately, depending on the method the results will vary. So the three most common methods are random, fasting, and a two-hour glucose tolerance test which we'll just abbreviate GTT. Now we'll bring in the the different diagnostic levels here, however the exact numbers for each of these categories are less important than a couple of trends. And the first one is that regardless of the method: random, fasting, or the two-hour glucose tolerance test, a blood glucose level of greater than or equal to 200 mg/dL is consistent with diabetes. But this number is slightly lower if fasting blood glucose levels is used. Then the level is 126 mg/dL. Then the last important point to mention is that a random glucose test can not be used to diagnose pre-diabetes. You need either a fasting or a two-hour glucose tolerance test. Now, fortunately hemoglobin A1C testing is a little bit more straight forward, as the timing of the test does not matter. And then similarly to the blood glucose test, there's one important number to remember. And that is that a level greater than or equal to 6.5% is consistent with diabetes mellitus. So now that we have a better understanding of the clinical presentation of diabetes mellitus and the laboratory tests, let's bring these two components together to discuss how the diagnosis of diabetes mellitus is made. Neither the presentation or the diagnostic tests alone is enough to diagnose diabetes. The diagnosis is made by a combination of the two. And there are two ways diabetes mellitus can be diagnosed, and they're based on different presentations. So first, if an individual has symptoms of diabetes, whether acute or subacute, then only one positive test, either the blood glucose or the hemoglobin A1C is necessary for the diagnosis of diabetes mellitus. However, if the individual is asymptomatic, then a diagnosis of diabetes mellitus requires two positive tests that are separated by at least one week of time.