What is the recommended blood glucose level for a Positron Emission Tomography (PET) scan?

Blood Glucose Requirements for PET Scans

For clinical PET scans, blood glucose levels should be below 11 mmol/L (200 mg/dL) to proceed with the examination, while research studies require stricter control with levels between 7-8.3 mmol/L (126-150 mg/dL). 1

Blood Glucose Thresholds by Scan Type

For Clinical FDG PET/CT Studies:

• Maximum acceptable level: <11 mmol/L (200 mg/dL) 1
• Minimum acceptable level: >4 mmol/L (70 mg/dL) 1
• Optimal range: 4-7 mmol/L (70-126 mg/dL) 1

For Research FDG PET/CT Studies:

• Maximum acceptable level: 7-8.3 mmol/L (126-150 mg/dL) 1
• Specific thresholds should be defined in the study protocol

For Atherosclerosis Imaging:

• Maximum acceptable level: <7.2 mmol/L (130 mg/dL) 1

Impact of Blood Glucose Levels on Scan Quality

High blood glucose significantly impacts diagnostic accuracy:

• In patients with bacteremia, detection rates drop dramatically with rising glucose levels 2:
  • 61-65% detection rate with glucose 3.0-7.9 mmol/L (54-142 mg/dL)
  • 30-38% detection rate with glucose 8.0-10.9 mmol/L (144-196 mg/dL)
  • Only 17% detection rate with glucose >11.0 mmol/L (200 mg/dL)

Patient Preparation Protocol

1. Fasting requirements:

   • Fast for at least 4 hours before the scan 1, 3
   • Maintain adequate hydration with plain water 3

2. Blood glucose measurement:

   • Check glucose upon patient arrival 1
   • For diabetic patients, check immediately upon arrival to allow time for correction 1, 3

3. When glucose is elevated:

   • If glucose ≥11 mmol/L (200 mg/dL): Reschedule the scan 1
   • For levels between 7-11 mmol/L (126-200 mg/dL): Proceed with clinical scans but note potential reduced sensitivity 1, 2

Managing Hyperglycemia for PET Scans

If blood glucose correction is needed:

• Do not administer insulin less than 4 hours before FDG injection 1
  • Insulin administration increases muscle uptake of FDG, reducing scan quality 1, 4
• If insulin is required, use rapid-acting insulin via subcutaneous injection 1
• Wait at least 4 hours between insulin administration and FDG injection 4
• For patients on metformin requiring IV contrast, discontinue metformin at the time of procedure and withhold for 48 hours after 1

Special Considerations

• Non-diabetic patients rarely have glucose levels >150 mg/dL, so routine glucose testing may be limited to diabetic patients 5
• For patients with unstable or poorly controlled diabetes, hyperglycemia should not be considered an absolute contraindication to the study 1
• Glucose correction formulas exist but have limited validation in clinical practice 1
• Emerging evidence suggests empagliflozin (20mg) may help achieve optimal blood glucose levels for PET scans in patients with hyperglycemia 6

Documentation Requirements

• Always record and report blood glucose levels with scan results 1
• Document whether SUV values are corrected for glucose 1
• For sequential studies, use validated methods for glucose measurement rather than bedside devices 1

Remember that while guidelines permit scanning with glucose levels up to 200 mg/dL, recent evidence suggests diagnostic accuracy begins to decline significantly at much lower levels (>144 mg/dL) 2, so optimal glycemic control is crucial for maximizing diagnostic value.