What laboratory tests do you order for a diabetic patient?

Laboratory Tests for Diabetic Patients

For routine monitoring of diabetic patients, order hemoglobin A1c every 3-6 months, annual urine albumin-to-creatinine ratio, and fasting plasma glucose as needed to assess glycemic control and screen for complications. 1, 2

Core Laboratory Tests

Hemoglobin A1c (HbA1c)

• Measure HbA1c every 3 months until glycemic targets are achieved, then at least every 6 months for patients meeting goals 1, 2
• Measure quarterly in patients not meeting glycemic goals or with recent treatment changes 1
• Only use NGSP-certified methods in accredited laboratories 1, 2, 3
• HbA1c reflects average glucose levels over the past 60-90 days and predicts risk for chronic complications 4, 1

Important caveat: HbA1c may be unreliable in conditions affecting red blood cell turnover including sickle cell disease, pregnancy, hemodialysis, recent blood loss or transfusion, and erythropoietin therapy 1, 3. In these situations, use only plasma glucose criteria for monitoring 1, 3.

Fasting Plasma Glucose (FPG)

• Measure after at least 8 hours of fasting 1, 2
• Collect samples in tubes containing citrate buffer or place immediately in ice-water slurry and centrifuge within 15-30 minutes to minimize glycolysis 1, 2
• Use FPG values to titrate basal insulin in insulin-treated patients 5

Urine Albumin-to-Creatinine Ratio (uACR)

• Measure annually in all adults with diabetes using first morning void spot urine samples 1, 2
• For type 1 diabetes, begin annual testing in pubertal or post-pubertal individuals 5 years after diagnosis 3
• Increase frequency to every 6 months if estimated glomerular filtration rate is <60 mL/min/1.73 m² and/or albuminuria is >30 mg/g creatinine 1, 2, 3
• First morning void samples are preferred to minimize variability 2

Additional Testing Based on Clinical Context

Lipid Profile

• Measure to assess cardiovascular risk factors, particularly in patients with hypertension, low HDL cholesterol, or high triglycerides 1

C-peptide

• Order when distinguishing type 1 from type 2 diabetes in ambiguous cases, such as individuals with type 2 phenotype who present in ketoacidosis 1, 2, 3
• For insulin pump therapy coverage, measure fasting C-peptide when simultaneous fasting plasma glucose is <220 mg/dL 2

Blood Ketones

• Use for diagnosis of diabetic ketoacidosis and monitoring during treatment 1, 3
• Recommended for individuals prone to ketosis when they have unexplained hyperglycemia or symptoms of ketosis 1

Autoantibody Testing (Type 1 Diabetes)

• Order standardized islet autoantibody tests in adults when there is phenotypic overlap between type 1 and type 2 diabetes 3
• Key autoantibodies include islet cell autoantibodies, glutamic acid decarboxylase autoantibodies, insulin autoantibodies, tyrosine phosphatase autoantibodies, and zinc transporter 8 autoantibodies 3

Quality Assurance Considerations

• Point-of-care A1C testing should be restricted to FDA-approved devices at CLIA-certified laboratories that perform testing of moderate complexity or higher 1, 3
• Glucose measurement should have analytical imprecision ≤2.4%, bias ≤2.1%, and total error ≤6.1% 2
• Urine albumin measurement should have between-day precision ≤6%, bias ≤7% to 13%, and total allowable error ≤24% to 30% 2

Common Pitfalls

• A1C does not provide a measure of glycemic variability or hypoglycemia, which are important factors in diabetes management 1, 3
• For patients with conditions interfering with A1C interpretation, use alternative approaches such as self-monitoring of blood glucose, continuous glucose monitoring, or glycated serum protein assays 1
• Routine laboratory blood glucose testing by healthcare providers should no longer be used to assess glycemic control except to supplement information from other testing methods and to verify accuracy of self-monitoring 4
• Timed urine collections for albumin should be done only in research settings and should not guide clinical practice 3