Tests

1st tests to order

HbA1c

Test
Result
Test

Confirm an abnormal result in asymptomatic individuals with a repeat HbA1c or another diabetes diagnostic test.[1]​ Reflects the average degree of hyperglycemia over the preceding 2 to 3 months.[1]​ Result can be affected by factors affecting hemoglobin concentrations or red blood cell turnover, and may not be a suitable diagnostic test in those with some hemoglobin variants, anemia (or recent blood loss or transfusion), or those undergoing treatment with hemodialysis, erythropoietin, or for HIV.[1]​ Pregnancy (second and third trimesters and the postpartum period) can also affect the result.[1]​ In such instances plasma glucose criteria should instead be used for diagnosis.[1]​ An HbA1c result that does not appear concordant with other blood glucose results should prompt consideration of potential problems or interference with either test.[1]​

Result

≥6.5% (≥48 mmol/mol)

fasting plasma glucose

Test
Result
Test

Fasting is defined as no caloric intake for at least 8 hours.[1]​​

Confirm an elevated result with an HbA1c (which can be done on the same sample), a second fasting plasma glucose, or another diabetes diagnostic test.[1]​​

Result

≥126 mg/dL (≥7.0 mmol/L)

2-hour post-glucose load plasma glucose

Test
Result
Test

Plasma glucose is measured 2 hours after 75 g oral glucose load.[1]​​

Patients should be advised to consume a varied diet with at least 150 g of carbohydrate on the 3 days prior to testing, as fasting and carbohydrate restriction can falsely increase plasma glucose levels.[1]​​

Confirm an elevated result with an HbA1c (which can be done on the same sample), a second 2-hour plasma glucose, or another diabetes diagnostic test.[1]​​

Result

≥200 mg/dL (≥11.1 mmol/L)

random plasma glucose

Test
Result
Test

Confirms diagnosis in the presence of symptoms of hyperglycemia or hyperglycemic crisis (e.g., polyuria, polydipsia, blurred vision, and unexplained weight loss.[1]​​

Result

≥200 mg/dL (≥11.1 mmol/L)

Tests to consider

plasma or urine ketones

Test
Result
Test

In the presence of hyperglycemia suggest type 1 diabetes.

Result

medium or high quantity

fasting C-peptide

Test
Result
Test

C-peptide is a byproduct formed when proinsulin is processed to insulin. Therefore, its levels reflect insulin production. Half life of C-peptide is 3 to 4 times longer than that of insulin.

Low or undetectable C-peptide level indicates absence of insulin secretion from pancreatic beta cells.

C-peptide testing can be used when there is uncertainty about type 1 diabetes diagnosis and can help identify people who should have genetic testing for monogenic diabetes.[1]​

Result

low or undetectable

autoimmune markers

Test
Result
Test

These include autoantibodies to glutamic acid decarboxylase, insulin, islet cells, islet antigens (IA2 and IA2-beta), and the zinc transporter ZnT8.​[1]

Presence of autoantibodies in an individual presenting with diabetes is in keeping with a diagnosis of type 1 diabetes.[1]​​

Result

positive

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