What labs should be ordered to monitor diabetes?

Laboratory Tests for Diabetes Monitoring

The most important laboratory tests for monitoring diabetes include hemoglobin A1c (HbA1c), fasting plasma glucose, and urine albumin-to-creatinine ratio, which should be ordered regularly to assess glycemic control and screen for complications. 1

Core Laboratory Tests

Glycemic Control Assessment

• HbA1c: Should be measured routinely every 3 months until acceptable targets are reached, then at least every 6 months to assess long-term glycemic control 2
• Fasting Plasma Glucose (FPG): Should be measured in venous plasma, with samples collected after at least 8 hours of fasting 1
• To minimize glycolysis in FPG samples: Use tubes containing granulated citrate buffer or place sample immediately in ice-water slurry and centrifuge within 15-30 minutes 1

Kidney Function Monitoring

• Urine Albumin-to-Creatinine Ratio (uACR): Should be measured annually in all adults with diabetes using morning spot urine samples 1
• First morning void urine samples are preferred for uACR measurement to minimize variability 1
• More frequent uACR testing (every 6 months) is needed if estimated glomerular filtration rate is <60 mL/min/1.73 m² and/or albuminuria is >30 mg/g creatinine 1

Timing of Laboratory Tests

Initial Diagnosis

• For type 1 diabetes: Plasma glucose rather than HbA1c is recommended for diagnosis in individuals with symptoms of hyperglycemia 3
• For type 2 diabetes: HbA1c ≥6.5% (≥48 mmol/mol) can be used for diagnosis 2

Regular Monitoring Schedule

• HbA1c: Every 3 months until target is reached, then at least every 6 months 2
• Urine albumin screening: Begin annual testing in pubertal or post-pubertal individuals 5 years after diagnosis of type 1 diabetes and at the time of diagnosis of type 2 diabetes 1
• Liver enzyme monitoring: Prior to initiation of certain medications (like thiazolidinediones) and periodically thereafter 4

Special Considerations

Autoantibody Testing

• Pancreatic autoantibodies (ICA, GAD65, insulin autoantibodies, IA-2, IA-2β, ZnT8) may be measured to confirm the autoimmune nature of type 1 diabetes 3
• Screening for islet autoantibodies in relatives of individuals with type 1 diabetes is recommended only in research settings or as an option for first-degree relatives 1

C-peptide Testing

• C-peptide measurements may help distinguish type 1 from type 2 diabetes in ambiguous cases, such as individuals with type 2 phenotype who present in ketoacidosis 1
• For insulin pump therapy coverage: If required by payers, measure fasting C-peptide when simultaneous fasting plasma glucose is <220 mg/dL 1

Tests Not Routinely Recommended

• Routine insulin or proinsulin testing is not recommended for most people with diabetes 1
• Insulin antibody testing has no published evidence to support its use for routine care 1
• Timed collections for urine albumin should be done only in research settings 1

Quality Assurance Considerations

• HbA1c testing should only use NGSP-certified methods in accredited laboratories 2
• Analytical performance goals for urine albumin measurement: Between-day precision ≤6%, bias ≤7% to 13%, and total allowable error ≤24% to 30% 1
• Glucose measurement should have analytical imprecision ≤2.4%, bias ≤2.1%, and total error ≤6.1% 1

By following these guidelines for laboratory monitoring, clinicians can effectively track glycemic control and detect early signs of diabetes-related complications, ultimately improving patient outcomes.