Patients with prediabetes often have no specific differentiating signs or symptoms.
Fasting plasma glucose level is 100-125 mg/dL in prediabetes.
2-hour post-load glucose after 75 g of oral glucose is 140-199 mg/dL in prediabetes.
HbA1c of 5.7% to 6.4% indicates prediabetes and high risk of future diabetes.
Onset often at age <35 years, but can occur in older individuals.
Many patients are not obese.
More commonly presents with symptoms (polyuria, polydipsia, weight loss, generalized weakness, blurred vision) and ketosis, rather than being detected by screening.
Urine ketones are often present in type 1 diabetes, but may be positive in type 2 diabetes if there is severe volume depletion.
Low (<0.6 nanogram/mL) or absent C-peptide level.
One or more autoantibodies (antiglutamic acid decarboxylase [GAD] antibodies, islet cell antibodies [ICA], insulin autoantibodies, autoantibodies to the tyrosine phosphates IA-2 and IA-2beta) are present in 85% of patients with type 1 at the time of diagnosis, but may disappear within a few years. Type 1 diabetes is defined by the presence of one or more of these autoimmune markers, but testing is usually not required for diagnosis.
Glucose screening criteria cannot be used to differentiate type 1 and type 2 diabetes, as they are identical.
Typical age of onset of diabetes is over 30 years old. Patients are usually nonobese and respond initially to lifestyle modifications and oral agents. Production of insulin gradually decreases (between 6 months and 5 years), such that treatment with insulin is required.
LADA is considered a subset of type 1 diabetes; however, patients with LADA are frequently misclassified as having type 2 diabetes.
Positive for at least 1 of the 4 antibodies commonly found in type 1 diabetic patients (ICAs and autoantibodies to GAD65, IA-2, and insulin).
Maturity-onset diabetes of the young (MODY) is the most common form of monogenic diabetes and affects 1% to 2% of people with diabetes.
MODY is caused by mutation of a single gene (i.e., monogenic). As of 2011, at least 11 forms of MODY are known.
It has autosomal dominant inheritance and should be suspected in cases of diabetes in nonobese, young patients (adolescence or young adult) with a family history of diabetes in two or more successive generations.
Patients are often misclassified as type 1 or type 2 diabetes. Insulin treatment is often not needed.
Genetic testing in patients with high index of suspicion (genes encoding glucokinase and transcription factors are identified).
Presents with unprovoked ketosis or ketoacidosis.
Considered an "idiopathic diabetes," as patients have no evidence of autoimmunity. Often misclassified as type 1 diabetes, as individuals have episodic ketoacidosis and exhibit varying degrees of insulin deficiency between episodes. However, a type 2 diabetes phenotype is common (obesity, insulin resistance, metabolic syndrome).
Patients are usually from a minority ethnic group, and have a positive family history of diabetes.
On discontinuation of insulin therapy, the period of near-normoglycemic remission may last for a few months to several years. However, almost half will be insulin dependent 10 years after diagnosis.
Absent islet cell autoantibodies.
C-peptide often low or undetectable during diabetic ketoacidosis; recovery may be used as reliable predictor of insulin discontinuation.
Only occurs during pregnancy.
Gestational diabetes is generally detected by screening during pregnancy. Based on the current evidence, the US Preventive Services Task Force recommends screening for gestational diabetes in asymptomatic pregnant women after 24 weeks of gestation. One-step or 2-step screening strategies may be used.
When overt hyperglycemia occurs during pregnancy, it may be difficult to distinguish between undetected preexisting type 2 diabetes and gestational diabetes.
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