This is the first post of a series where we'll review and summarize the Standard of Medical Care in Diabetes that are annually published by the ADA. Here goes the first part of the section "Classification and diagnosis of Diabetes", that you can see complete in https://care.diabetesjournals.org/content/43/Supplement_1/S14
As in previous years, they propose a classification in 4 groups: Type 1 diabetes, Type 2 diabetes, Gestational diabetes, and Specific types. This last group is very extense and heterogeneous, including MODY, neonatal, or secondary to drugs, pancreatic diseases, endocrinopathies, etc.
After commenting on problems of misdiagnosis due to atypical presentations, there is a review of pathophysiology. In type 1 diabetes there are three distinct stages: Stage 1, with at least 2 positive autoAb and normoglycemia; Stage 2, with IFG or IGT, and Stage 3, with clinical diabetes. In type 2 diabetes the underlying process is more complex.
Then, diagnostic criteria for diabetes are explained. They haven't changed from previous years: 1.-FPG >=126 mg/dL; 2.-75g OGTT with glucose 2h >=200 mg/dL; 3.-Standarized A1c >=6,5%; 4.-Symptoms of diabetes or hyperglycemic crisis with glucemia >=200 mg/dL. It's necessary at least 2 of those criteria in the same or different samples unless unequivocal hyperglycemia is present. FPG, 75g OGTT and A1c are equally valid, although they do not detecty diabetes in the same individuals (low concordance).
A1c Testing
To be valid it must be standarized to DCCT. As a diagnostic method it has advantages (less variability, no need for fasting) and disadvantages (expensive, less available, lower sensitivity). It is an indirect test that varies according to age, race, pregnancy, hemoglobinopathies, and genetics. Age: although inicially validated only in adults, currently it can also be used in children and adolescents. Race and Hbpathies: African Americans have higher A1c values for the same glycemia, and they can have HbS or G6PDH G202A that renders lower A1c readings. Other conditions: in high red blood cell turnover conditions such as sickle cell disease, pregnancy, glucose-6-phosphate dehydrogenase deficiency, hemodialysis, recent blood loss or transfusion, or erythropoietin therapy, A1c can be lower. It is also unreliable in iron deficiency anemia, or HIV drugs.
Type 1 diabetes.
Autoantibodies such as GAD, IA-2, IA-2 beta, and Zinc Transporter 8 are markers of type 1 diabetes, that accounts for 5-10% of all cases. They can be tested in first degree family members of a proband with T1DM for clinical trial purposes. T1DM is HLA linked with DQA and DQB genes. Idiopatic type 1 diabetes is a very unfrequent type. Ab are negative, asian and african origin is more usual, and insulin needs vary, alternating DKA with insulin-free periods. There are no established screening programs for type 1 diabetes, in first-degree relatives antoAb could be proposed in clinical research setting.
Prediabetes and type 2 diabetes screening. It should be considered in:
- Overweight or obese adults with at least one of:
- 1st degree relative
- High risk ethnicity
- CVD
- Hypertension (140/90 or treatment)
- Triglycerides >250 or HDL <35 mg/dL
- Physical inactivity
- Women with PCOS
- Other insulin-resistance conditions
- Overweight or obese women planning pregnancy
- Adults >45 If normal, repeat screening every 3 years.
- Childern or teenagers with overweight or obesity and at least one of:
- Maternal GDM
- Relative with T2DM
- Insulin-resistance conditions
- High risk race/ethnicity
Prediabetes. Defined as impaired fasting glucose IFG (100-125 mg/dL), impaired glucose tolerance IGT (2h post 75g 140-199 mg/dL) or A1c 5,7-6,4%, is not a clinical entity but a risk for diabetes. The WHO and other organizations define IFG with other range (110-125 mg/dL).Individuals with A1c 6-6,5% have a 25-50% 5-year risk of developing type 2 diabetes. This is 20 times higher that for someone with A1c 5%.
Type 2 diabetes. It includes 90-95% of cases of diabetes. Specific etiologies are unknown. Beta cell autoinmunity is absent, obesity is frequent, and its risk factors are those listed in the Screening section. Although it seems reasonable to screen high risk individuals, RCT showing cost-effectiveness of this practice are lacking. One European Study (ADDITION Europe) didn't find that screening reduced CVD or mortality. The ADA has a Diabetes Riks Test that can be a guide for screening programs in different settings:
So far this part. In the next post we'll review the screening and management of specific types of diabetes: Cystic fibrosis, post-transplantation, monogenic, pancreatic, and gestational diabetes. We'd be glad to receive your comments, bye.
