What laboratory tests should be drawn for a patient with type 2 diabetes mellitus (T2DM)?

Laboratory Tests for Type 2 Diabetes

All patients with type 2 diabetes require routine monitoring with hemoglobin A1c (HbA1c) every 3-6 months, annual urine albumin-to-creatinine ratio (uACR), and periodic fasting plasma glucose (FPG), along with lipid profiles to assess cardiovascular risk. 1, 2

Core Laboratory Tests

Hemoglobin A1c (HbA1c)

• Measure HbA1c every 3 months until glycemic targets are reached, then at least every 6 months thereafter 1, 2
• For patients not meeting glycemic goals or with recent treatment changes, continue quarterly testing 2
• HbA1c reflects average glucose levels over the preceding 60-90 days and should be measured using only NGSP-certified methods in accredited laboratories 1, 2
• Target HbA1c <7% (<53 mmol/mol) for most nonpregnant adults with diabetes 1

Fasting Plasma Glucose (FPG)

• Measure FPG regularly to complement HbA1c monitoring 2
• Requires at least 8 hours of fasting, with samples collected in tubes containing citrate buffer or placed immediately in ice-water slurry to prevent glycolysis 1
• FPG provides point-in-time glucose assessment and helps identify glycemic variability not captured by HbA1c 2

Urine Albumin-to-Creatinine Ratio (uACR)

• Measure uACR annually at the time of type 2 diabetes diagnosis using first morning void spot urine samples 1, 2
• If estimated glomerular filtration rate (eGFR) is <60 mL/min/1.73 m² and/or albuminuria is >30 mg/g creatinine, increase testing frequency to every 6 months 1, 2
• First morning void samples are preferred to minimize variability 1

Lipid Profile

• Measure lipid panel to assess cardiovascular risk factors, particularly important given that approximately one-third of adults with type 2 diabetes have cardiovascular disease 1, 3
• Focus on HDL cholesterol, LDL cholesterol, and triglycerides 1

Important Testing Considerations and Pitfalls

When HbA1c Cannot Be Used

• In conditions affecting red blood cell turnover, use only plasma glucose criteria (FPG or oral glucose tolerance test) 1, 2
• These conditions include: sickle cell disease, pregnancy (second and third trimesters), hemodialysis, recent blood loss or transfusion, erythropoietin therapy, glucose-6-phosphate dehydrogenase deficiency, HIV, iron-deficiency anemia, and hemoglobin variants 1, 2
• Marked discordance between HbA1c and plasma glucose levels should raise suspicion of assay interference from hemoglobin variants 1, 2

Quality Assurance

• Only use point-of-care A1c testing with FDA-approved devices at CLIA-certified laboratories performing moderate complexity testing or higher 2
• HbA1c assays must be certified by the National Glycohemoglobin Standardization Program (NGSP) and standardized to the Diabetes Control and Complications Trial (DCCT) reference 1

Additional Laboratory Tests Based on Clinical Context

For Diagnostic Uncertainty

• C-peptide measurement helps distinguish type 1 from type 2 diabetes in ambiguous cases 2
• Standardized islet autoantibody tests are recommended when there is phenotypic overlap between type 1 and type 2 diabetes 1

For Acute Complications

• Blood ketone determinations should be used for diagnosis of diabetic ketoacidosis and monitoring during treatment 2
• Blood ketone testing is recommended for individuals prone to ketosis when they have unexplained hyperglycemia or symptoms of ketosis 2

Renal Function Monitoring

• Measure serum creatinine and calculate eGFR to assess kidney function, particularly important as 10.1% of patients with type 2 diabetes have kidney failure 3
• More frequent monitoring is needed when eGFR falls below 60 mL/min/1.73 m² 1

Common Pitfalls to Avoid

• Do not rely solely on HbA1c for glycemic assessment—it does not provide information about glycemic variability or hypoglycemia, which are critical factors in diabetes management 2
• Avoid using wrong collection tubes or delayed processing for glucose samples—this causes falsely low values due to glycolysis 2
• Do not use random capillary blood glucose for routine screening—it is less well standardized than FPG 1
• Be aware that laboratories must consider potential interferences from hemoglobin variants in their patient population when selecting HbA1c assay methods 1