Investigations

1st investigations to order

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Order after a minimum 8-hour fast. 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.[2]

Result

>125 mg/dL

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Confirm with a repeat HbA1c or another diagnostic test.[2] HbA1c is also used to monitor glycemic control, usually every 3-6 months.

Result

6.5% or greater

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More costly and inconvenient than fasting plasma glucose or HbA1c, and not commonly used for diagnosis of type 2 diabetes.[2]

Result

≥200 mg/dL

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Nonfasting test. Convenient, but less accurate than either fasting plasma glucose, HbA1c, or 75 g oral glucose tolerance test. Used for rapid assessment of glucose status if symptoms such as polyuria, polydipsia, or weight loss are present.[2]

Result

≥200 mg/dL

Investigations to consider

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Urine ketones should be checked if patients are symptomatic of hyperglycemia (polyuria, polydipsia, weakness) and volume depletion (dry mucous membranes, poor skin turgor, tachycardia, hypotension, and, in severe cases, shock) at diagnosis or throughout course of disease. Ketoacidosis is a common presentation of type 1 diabetes, but can also occur in type 2 diabetes.[50][46][47] Although by definition hyperosmolar hyperglycemic state is characterized by negative ketone bodies, mild-to-moderate ketonemia may be present.[48]

Result

positive in instances of ketoacidosis

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Not done routinely for diagnosis of diabetes, but may be useful in differentiating type 1 and type 2 diabetes.[51] Absolute insulin deficiency is a key feature of type 1 diabetes, which results in low (<0.2 nanomol/L) or undetectable levels of plasma C-peptide.[2][51] C-peptide results must be interpreted in clinical context of disease duration, comorbidities, and family history.[52] Although C-peptide can be helpful in evaluating the endogenous production of insulin, both type 1 and type 2 diabetes can be associated with insulinopenia, and endogenous insulin production can be detected in some individuals with type 1 diabetes for prolonged periods of time after diagnosis, especially in individuals diagnosed in adulthood.

Result

>1 nanomol/L

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Not done routinely for diagnosis of diabetes, but is an option for differentiating type 1 and type 2 diabetes. Autoantibodies to glutamic acid decarboxylase 65 (GAD65), islet cell antibodies (ICA), insulin antibodies, antibodies to tyrosine phosphatase-related islet antigen-2 (IA-2 and IA-2beta), and zinc-transporter-8 antibodies (ZnT8) can help to identify individuals with immune-mediated diabetes, although these antibodies fade with time after the onset of illness.[2][53][54]

Result

presence suggests immune-mediated diabetes

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Indicates nephropathy and suggests possible other microvascular damage. Monitored yearly.

May be assessed with albumin-to-creatinine ratio in a random urine sample.[2]

Result

may be increased

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GFR is calculated according to the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) or Modification of Diet in Renal Disease (MDRD) formulas. The CKD-EPI formula is now recommended by the Kidney Disease Outcomes Quality Initiative (KDOQI) because it removes bias at higher GFR levels, allowing for reporting across a full range.

Result

may show renal insufficiency

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Dyslipidemia is common in type 2 diabetes, especially low HDL and high triglycerides.

Result

may show high LDL, low HDL, and/or high triglycerides

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Baseline assessment. A normal ECG does not rule out coronary artery disease. Patients with an abnormal resting ECG may require further cardiac investigation.[2]

Result

may indicate prior ischemia

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A noninvasive tool to detect peripheral arterial disease (PAD), which has a high prevalence in patients with diabetes. The American Diabetes Association recommends that ABI should be performed in patients with symptoms of PAD.[2] Can be used to screen for PAD.

Result

≤0.9 is abnormal

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Due to the potential for calcification of the arteries from atherosclerotic peripheral vascular disease (which falsely elevates ABI), toe pressure testing is often done as an adjunct to ABI testing.[55] 

Result

≤0.7 is abnormal

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Patients should be referred to an ophthalmologist at the time of diagnosis of type 2 diabetes, as patients may have had years of undiagnosed diabetes and some manifestation of diabetic retinopathy is present in about 30% of patients.[56] 

Result

may show retinopathy

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