What investigations should be sent for a patient with uncontrolled sugars?

Investigations for Uncontrolled Diabetes

For a patient with uncontrolled sugars, you should immediately order hemoglobin A1c (HbA1c), fasting plasma glucose (FPG), and urine albumin-to-creatinine ratio (uACR) to assess glycemic control and screen for complications. 1

Core Laboratory Tests to Order

Hemoglobin A1c (HbA1c)

• Order HbA1c as your primary test to assess glycemic control over the past 60-90 days 1
• Use only NGSP-certified methods in accredited laboratories 1
• This test reflects average glucose levels and should be measured routinely every 3 months until acceptable targets are reached, then at least every 6 months 1
• HbA1c ≥6.5% on two separate occasions confirms diabetes diagnosis 2, 1

Fasting Plasma Glucose (FPG)

• Draw blood after at least 8 hours of fasting 2, 1
• Place the sample tube immediately in an ice-water slurry and separate plasma from cells within 30 minutes to minimize glycolysis 2
• Alternatively, use tubes containing citrate buffer (not just sodium fluoride) for effective glycolysis inhibition 2, 1
• FPG ≥126 mg/dL on two separate occasions confirms diabetes 2, 1

Urine Albumin-to-Creatinine Ratio (uACR)

• Measure uACR annually in all adults with diabetes using morning spot urine samples 1
• This screens for diabetic kidney disease, a critical microvascular complication 1
• If estimated glomerular filtration rate is <60 mL/min/1.73 m² or albuminuria is >30 mg/g creatinine, increase testing frequency to every 6 months 1

Additional Tests Based on Clinical Context

Lipid Profile

• Order a complete lipid panel to assess cardiovascular risk, particularly important given that cardiovascular disease is the leading cause of death in diabetes 2, 1
• This is especially critical if the patient has hypertension, low HDL cholesterol, or high triglycerides 1

Blood Ketone Testing

• Order blood ketone determinations if the patient has unexplained hyperglycemia or symptoms of ketosis (nausea, vomiting, abdominal pain, fruity breath) 1
• This is essential for diagnosing diabetic ketoacidosis and may be used for monitoring during treatment 1

C-Peptide Level

• Consider ordering C-peptide measurement if there is diagnostic uncertainty between type 1 and type 2 diabetes 2, 1
• This helps assess residual beta cell function 2

Important Caveats About HbA1c Testing

HbA1c may not be reliable in several conditions affecting red blood cell turnover: 1

• Sickle cell disease
• Pregnancy
• Hemodialysis
• Recent blood loss or transfusion
• Erythropoietin therapy

In these situations, use only plasma blood glucose criteria for diagnosis and monitoring 1. Alternative approaches include self-monitoring of blood glucose, continuous glucose monitoring, or glycated serum protein assays 1.

Confirmation of Results

• In the absence of unequivocal hyperglycemia (random glucose ≥200 mg/dL with classic symptoms), confirm results by repeat testing 2, 1
• The second test may be a repeat of the initial test or a different test, performed without delay 2
• If two different tests (such as A1C and FPG) are both above the diagnostic threshold from the same sample, repeat testing in 3-6 months 2

Common Pitfalls to Avoid

• Do not rely on point-of-care A1C testing unless using FDA-approved devices at CLIA-certified laboratories performing moderate complexity testing or higher 1
• Do not use random blood glucose testing alone for routine monitoring—it has low sensitivity (39-55%) despite high specificity (92-98%) 2
• Avoid using laboratory plasma glucose testing as the primary means of routine outpatient monitoring—HbA1c is superior for this purpose 2
• Remember that A1C does not provide information about glycemic variability or hypoglycemia, which are important management factors 1