What laboratory tests should be ordered for patients with diabetes mellitus (DM) in a primary care clinic versus an endocrinology clinic?

From the Guidelines

For diabetic patients, the essential laboratory tests include hemoglobin A1C (every 3-6 months), fasting blood glucose, comprehensive metabolic panel, lipid panel (annually), urinalysis with microalbumin-to-creatinine ratio (annually), and TSH (thyroid function), with the frequency and specialization of tests differing between primary care and endocrinology clinics. In primary care settings, these core tests are typically ordered with a focus on overall diabetes management and screening for common complications, as outlined in the standards of care in diabetes 1. The tests should be performed at the following frequencies:

• Hemoglobin A1C: at least two times a year in patients who are meeting treatment goals, and quarterly in patients whose therapy has changed or who are not meeting glycemic goals 1.
• Lipid profile: annually, including total, LDL, and HDL cholesterol and triglycerides 1.
• Liver function tests: annually, as part of the comprehensive metabolic panel 1.
• Spot urinary albumin-to-creatinine ratio: annually, to assess kidney damage 1.
• Serum creatinine and estimated glomerular filtration rate: annually, with more frequent monitoring in patients with known chronic kidney disease or changes in medications that affect kidney function and serum potassium 1.
• Thyroid-stimulating hormone: annually in people with type 1 diabetes, and as indicated in people with type 2 diabetes 1. Endocrinology clinics may order additional specialized tests, such as C-peptide levels, autoantibody testing, and detailed insulin levels, and may perform more comprehensive thyroid testing beyond TSH alone 1. The difference primarily lies in test frequency and specialization rather than the core panel itself, with primary care handling routine monitoring and endocrinology managing complex cases requiring more detailed metabolic assessment 1. Regular laboratory monitoring is crucial because diabetes affects multiple organ systems, and early detection of complications allows for timely intervention to prevent disease progression, as emphasized in the executive summary of guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus 1.

From the Research

Laboratory Tests for Diabetes Mellitus (DM) in Primary Care and Endocrinology Clinics

The following laboratory tests are recommended for patients with diabetes mellitus:

• Plasma glucose measurement 2, 3, 4, 5
• Hemoglobin A(1c) (Hb A(1c)) concentrations 2, 4, 5, 6
• Urine albumin measurement 2, 5
• Microalbuminuria test 5
• Self-monitoring of plasma or blood glucose with meters 2

Specific Considerations for Primary Care Clinics

In primary care clinics, the following tests are relevant:

• Plasma glucose measurement to diagnose and monitor diabetes 3, 4
• Hb A(1c) concentrations to monitor glycemic control 2, 5

Specific Considerations for Endocrinology Clinics

In endocrinology clinics, additional tests may be considered:

• Genetic testing 2
• Measurement of autoantibodies 2
• Insulin, proinsulin, and C-peptide measurement 2
• Fructosamine measurement 6
• Total glycated plasma proteins (GPP) measurement 6

Special Considerations for Patients with End-Stage Renal Disease (ESRD)

For patients with ESRD, the following should be noted:

• Hemoglobin A1C (A1C) may be unreliable due to anemia, shortened red blood cell survival, and assay interferences from uremia 6
• A1C values above 7.5% may overestimate hyperglycemia in patients with ESRD 6