How to manage hypoglycemia (low blood sugar) during preparation for a Positron Emission Tomography (PET) Computed Tomography (CT) scan?

Management of Hypoglycemia During PET-CT Preparation

If blood glucose falls below 4 mmol/L (70 mg/dL) during PET-CT preparation, immediately administer 15-20 grams of oral glucose (preferably dextrose tablets), recheck glucose at 15-minute intervals, and repeat treatment until levels normalize above 70 mg/dL before proceeding with FDG injection. 1, 2

Blood Glucose Monitoring Requirements

• Check blood glucose upon patient arrival at the imaging center to identify levels that are too low (below 4 mmol/L or 70 mg/dL) or too high, avoiding unnecessary waiting time 1
• Use a calibrated glucometer or bedside glucose measurement device for screening purposes 1
• Blood glucose must be measured again immediately prior to FDG administration 1

Immediate Treatment Protocol for Hypoglycemia

For Conscious Patients Who Can Swallow

• Administer 15-20 grams of oral glucose in the form of dextrose tablets as first-line treatment 2
• Glucose tablets are preferred over other dietary sugars when available 2
• Recheck blood glucose every 15 minutes and repeat treatment until glucose returns to ≥70 mg/dL 2, 3

Alternative Oral Options When Glucose Tablets Unavailable

If dextrose tablets are not available, use alternatives containing at least 15 grams of simple sugars 2:

• 1 tablespoon table sugar
• 6-8 oz apple or orange juice
• 6-8 oz regular soda
• 1 tablespoon honey
• 15-25 jellybeans, gummy bears, or hard-shelled candies

For Patients Unable to Swallow or With Severe Hypoglycemia

• Do not administer oral glucose to patients who are not awake or unable to swallow 2
• Activate emergency medical services immediately for patients with severe hypoglycemia who cannot swallow, have seizures, or do not improve within 10 minutes of oral glucose 2
• For severe hypoglycemia, administer 25 mL of 50% dextrose via slow intravenous push 3
• Alternatively, use glucagon 1 mg intramuscularly (or 0.5 mg for patients <25 kg) when IV access is unavailable 3, 4

Timing Considerations for PET-CT Scanning

• Delay FDG injection until blood glucose is ≥4 mmol/L (70 mg/dL) to ensure adequate scan quality and patient safety 1
• After successful treatment of hypoglycemia and glucose normalization, the patient may proceed with the scan 1
• The upper acceptable limit for clinical PET-CT is <11 mmol/L (200 mg/dL) 1

Special Considerations for Diabetic Patients

Pre-Scan Medication Management

For patients with type 1 diabetes 1:

• Continue prescribed daily insulin doses when consuming meals
• Avoid short-acting insulin 4-6 hours before the study
• Sliding-scale insulin may be used during meal preparation but should be avoided on the day of the study

For patients with type 2 diabetes 1:

• Stop oral hypoglycemic medications during the fasting period and hold the morning dose
• Long-acting insulin (e.g., insulin glargine) the evening before is acceptable if needed
• No insulin should be taken 4-6 hours before the study

High-Risk Patient Identification

Patients at increased risk for hypoglycemia during PET-CT preparation include 3, 5:

• Those on insulin therapy or sulfonylureas
• Patients with history of hypoglycemia unawareness
• Those with recent episodes of severe hypoglycemia
• Patients with endogenous insulin deficiency

Post-Treatment Protocol

• Once blood glucose normalizes (≥70 mg/dL), give oral carbohydrates to restore hepatic glycogen and prevent recurrence before proceeding with FDG injection 4
• Continue monitoring glucose levels to ensure stability before administering FDG 1
• Document the hypoglycemic episode and glucose values for the medical record 1

Critical Pitfalls to Avoid

• Never proceed with FDG injection when glucose is <4 mmol/L (70 mg/dL), as this compromises both patient safety and scan quality 1
• Do not use glucose-containing IV fluids for hydration during the 4-hour fasting period, as this interferes with scan preparation 1
• Avoid administering insulin to correct hyperglycemia without adequate monitoring, as this may precipitate hypoglycemia 1
• Be aware that patients in starvation states, with adrenal insufficiency, or chronic hypoglycemia may not respond adequately to glucagon and require IV glucose instead 4
• High-dose vitamin C therapy can interfere with glucometer readings using the glucose oxidase method, potentially masking true glucose levels 6

When to Reschedule the Scan

• If hypoglycemia cannot be corrected within a reasonable timeframe (typically 30-60 minutes) 1
• If the patient experiences severe hypoglycemia requiring emergency intervention 2
• If the patient has recurrent hypoglycemia despite treatment, indicating inadequate glycemic control 3