28. Diagnostic criteria of diabetes mellitus (WHO criteria). Laboratory monitoring of patients with diabetic history

Diabetes mellitus (DM) is a group of disorders characterised by chronic hyperglycaemia due to abnormal carbohydrate metabolism. There are many types, but the most common types are type 1 diabetes mellitus and type 2 diabetes mellitus. DM is a very common disease, and the most common form, type 2, is associated with inactivity and obesity, which are increasing globally. Chronic hyperglycaemia causes severe long-term and short-term complications which may be lethal or cause significant morbidity.

There exists state of "prediabetes" where the carbohydrate metabolism is abnormal but not (yet) to such an extent that diabetes mellitus has manifested.

Diagnosis and evaluation

There are several ways to diagnose diabetes mellitus. If one fulfills any of the diagnostic criteria, they have DM.

Random plasma glucose

If one measures plasma glucose "randomly", i.e. without any preparation or fasting, and the result is > 11.1 mmol/L, they fulfill the diagnostic criterium of diabetes mellitus but only if they also have symptoms of diabetes mellitus. A random plasma glucose of 11.1 or higher in the absence of DM symptoms does not fulfill the criterium

Oral glucose tolerance test

The oral glucose tolerance test (OGTT) involves measuring blood glucose before and 2 hours after ingestion of 75 g oral glucose in a patient who has fasted for 12 hours, usually from the day before. It is mostly used to screen for gestational diabetes. If the blood glucose after 2 hours is 7.8 - 11.1, the patient has "impaired glucose tolerance" and is at risk for diabetes. If the blood glucose is > 11.1, the diagnostic criterium for diabetes is filled.

Fasting plasma glucose

Fasting plasma glucose (FPG) refers to measurement of plasma glucose after an overnight fast. If the FPG is 6.1 - 7.0, the patient has "impaired fasting glucose" and is at risk for diabetes. If the FPG is > 7.0, the diagnostic criterium for diabetes is filled.

HbA1c

Haemoglobin A1c (HbA1c) is a form of haemoglobin A with a glucose molecule bound to a specific point on its beta chain. The higher the serum blood glucose, the more haemoglobin A will be glycated, and the HbA1c level will increase. Because RBCs have a lifespan of around 120 days, the HbA1c level is proportional to the average blood glucose level for the last 120 days (3 months). Nowadays, the unit for HbA1c is mmol/mol (mmol of HbA1c divided by mol of regular Hb A), whereas previously one used a percentage unit.

The HbA1c is normally > 39 mmol/mol (< 5.7%). A result of 39 - 48 mmol/mol (5.7 - 6.5%) is significant for prediabetes, while 48 mmol/mol (6.5%) or higher fulfills the diagnostic criterium for diabetes mellitus.

Fructosamine and glycated albumin

It's possible to measure fructosamines (total glycated proteins in the serum) as well as glycated albumin levels to monitor 30-day average blood glucose level, but because these depend on the albumin level in the serum they are not reliable and are therefore rarely used. HbA1c is better suited.

Follow-up

Patients with diabetes should have regular follow-up to prevent complications. Examination is usually 2 – 4 times yearly. The body parameters, examination of the feet, HbA1c, and blood pressure should be measured. Kidney function tests, electrolytes, and liver function tests should be checked. A detailed eye examination should be done annually. Urinary albumin-to-creatine ratio should also be measured annually, to screen for diabetic nephropathy.