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Dr Geraint Preest, Clinical Section Editor at BMJ OnExamination, gives you some hints and tips for diagnosing diabetes.
The Royal College of General Practitioners highlighted diabetes, both type 1 and 2 as an area of weakness over several AKT sittings.
Diagnosis of diabetes is really important. It crops up many times in the AKT exam, so you really need to know this very well.
The first thing to know when you are diagnosing diabetes is that it depends whether the patient is symptomatic or asymptomatic. For symptomatic patients, a diagnosis of diabetes is based on a random blood glucose of 11 mmol/L or more. If it’s a fasting sample, then a diagnosis is based on a level of 7 mmol/L or more.
The Royal College have mentioned that candidates have struggled with glucose tolerance tests. If you look at the glucose tolerance test, then a level of 11.1 or more mmol/L is diagnostic of diabetes. This is a symptomatic patient. If the patient is asymptomatic, you need another reading on another occasion.
Most people are familiar with diagnosis of diabetes in most patients, but gestational diabetes is different and the thresholds are different. If you look at a fasting blood glucose for gestational diabetes is a level of 5.6 mmol/L or greater. A two hour postprandial glucose of greater than 7.8 mmol/L is diagnostic of gestational diabetes in a pregnant woman.
Diabetes can also be diagnosed on the basis on the HbA1c level. The threshold level is 48 mmol/L. A diagnosis is made if the HbA1c is greater than 48 mmol/L, but should remember the level of less than 48 mmol/L doesn’t exclude diabetes. There are a few exclusions for diagnosing diabetes from the HbA1c. It’s not used in children and young adults and it shouldn’t be used in Type 1 diabetes. As this is a measurement over a longer period of time, then you shouldn’t use it for patients who have been symptomatic for less than two months or if they are severely ill or taking medication that affects the blood glucose, such as prednisolone. The HbA1c method isn’t used in the diagnosis of gestational diabetes and in very rare instances you have to bear in mind patients with genetic conditions that may alter the HbA1c.