What laboratory tests do you order for patients with diabetes?

Laboratory Tests for Patients with Diabetes

For patients with diabetes, hemoglobin A1c (HbA1c) should be measured routinely every 3 months until acceptable targets are reached, then at least every 6 months, along with regular assessment of fasting plasma glucose and urine albumin-to-creatinine ratio to monitor glycemic control and screen for complications. 1

Core Laboratory Tests

• HbA1c should be measured routinely to document the degree of glycemic control, reflecting average glucose levels over the past 60-90 days 2, 3
• Fasting plasma glucose (FPG) should be measured after at least 8 hours of fasting, with samples collected in tubes containing citrate buffer or placed immediately in ice-water slurry to minimize glycolysis 1
• Urine albumin-to-creatinine ratio (uACR) should be measured annually in all adults with diabetes using morning spot urine samples to screen for diabetic kidney disease 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

Frequency of Testing

• HbA1c should be measured at least twice a year in patients meeting glycemic goals, and quarterly in patients not meeting goals or with recent treatment changes 2
• Patients with prediabetes (A1C ≥5.7% [39 mmol/mol], impaired glucose tolerance, or impaired fasting glucose) should be tested yearly 2
• Women with a history of gestational diabetes should have lifelong testing at least every 3 years 2

Special Considerations for HbA1c Testing

• Only NGSP-certified methods should be used in accredited laboratories 2, 3
• HbA1c may not be reliable in conditions affecting red blood cell turnover, such as:
  • Sickle cell disease
  • Pregnancy (second and third trimesters)
  • Hemodialysis
  • Recent blood loss or transfusion
  • Erythropoietin therapy 2
• In these cases, only plasma blood glucose criteria should be used for diagnosis and monitoring 2
• Marked discrepancies between measured A1C and plasma glucose levels should prompt consideration that the A1C assay may not be reliable for that individual 2

Additional Testing Based on Clinical Situation

• Lipid profile should be measured to assess cardiovascular risk factors, particularly in patients with hypertension, HDL cholesterol <35 mg/dL, or triglycerides >250 mg/dL 2
• C-peptide measurement may help distinguish type 1 from type 2 diabetes in ambiguous cases 1
• Blood ketone determinations (specifically β-hydroxybutyrate) should be used for diagnosis of diabetic ketoacidosis and may be used for monitoring during treatment 2
• Blood ketone testing is recommended for individuals prone to ketosis (those with type 1 diabetes, history of diabetic ketoacidosis, or treated with sodium-glucose transport protein 2 inhibitors) when they have unexplained hyperglycemia or symptoms of ketosis 2

Diagnostic Criteria for Diabetes

• Diabetes can be diagnosed by any of the following criteria:
  • HbA1c ≥6.5% (≥48 mmol/mol)
  • Fasting plasma glucose ≥126 mg/dL (7.0 mmol/L)
  • 2-hour plasma glucose ≥200 mg/dL (11.1 mmol/L) during oral glucose tolerance test
  • Random plasma glucose ≥200 mg/dL (11.1 mmol/L) with classic symptoms of hyperglycemia 2, 3
• In the absence of unequivocal hyperglycemia, results should be confirmed by repeat testing 2

Common Pitfalls and Caveats

• Point-of-care A1C testing for diabetes screening and diagnosis should be restricted to FDA-approved devices at CLIA-certified laboratories that perform testing of moderate complexity or higher 2
• A1C does not provide a measure of glycemic variability or hypoglycemia, which are important factors in diabetes management 2
• For patients with conditions that interfere with A1C interpretation, alternative approaches such as self-monitoring of blood glucose, continuous glucose monitoring, or glycated serum protein assays should be used 2
• Patients should be informed about the importance of frequent blood glucose monitoring to achieve effective glycemic control and avoid both hyperglycemia and hypoglycemia 4

By following these laboratory testing guidelines, clinicians can effectively monitor glycemic control and screen for complications in patients with diabetes, ultimately improving morbidity, mortality, and quality of life outcomes.