How should a patient with a pre-existing condition prepare for a medical exam?

Pre-Exam Preparation for Patients with Pre-Existing Conditions

Patients with pre-existing conditions must undergo specific preparation protocols tailored to their medical history and the type of examination being performed, with particular attention to medication management, fasting requirements, and risk factor assessment.

Essential Pre-Examination Assessment

Medical History Review

• Document all pre-existing conditions including diabetes, hypertension, cardiovascular disease, renal impairment, hepatic disease, thyroid disorders, and any autoimmune conditions 1
• Compile a complete medication list including prescription drugs, over-the-counter medications, vitamins, and herbal supplements 1, 2
• Assess for contraindications specific to the planned examination, such as contrast agent use in patients with renal impairment or iodinated procedures in patients on metformin 2
• Review family history of cardiovascular disease, diabetes, systemic hypertension, hyperlipidemia, and relevant genetic conditions 1

Condition-Specific Preparation Requirements

For Patients with Diabetes on Metformin

• Discontinue metformin at the time of or prior to iodinated contrast imaging procedures in patients with eGFR between 30-60 mL/min/1.73 m², those with hepatic impairment, alcoholism, heart failure, or those receiving intra-arterial iodinated contrast 2
• Re-evaluate eGFR 48 hours after the imaging procedure before restarting metformin 2
• Withhold metformin during surgical or other procedures requiring restricted food and fluid intake 2
• Monitor for lactic acidosis symptoms including unusual muscle pain, trouble breathing, unusual sleepiness, unexplained stomach problems, feeling cold in extremities, dizziness, or slow/irregular heartbeat 2

For Patients with Renal Impairment

• Obtain baseline eGFR before any examination involving contrast agents or nephrotoxic medications 2
• Ensure adequate prehydration with consumption of 1 liter of water 2 hours prior to procedures involving contrast to minimize kidney injury risk 1
• Adjust medication dosing based on renal function, particularly for renally excreted drugs 2

For Patients with Cardiovascular Disease

• Assess cardiac status with electrocardiography and echocardiography if the examination involves physical stress or sedation 1
• Additional cardiological work-up is required for patients with considerable cardiac risk factors or those aged >40 years 1
• Evaluate for conditions such as congestive heart failure, which increases risk of lactic acidosis and may require medication adjustments 2

For Patients with Endocrine Disorders

• Verify thyroid function and ensure thyroid blockade with saturated solution of potassium iodide before any [¹²³I]mIBG injection to prevent thyroid uptake of free iodide 1
• Assess adrenal function with morning cortisol/ACTH levels (ideally around 8 AM) in patients with suspected adrenal insufficiency 3
• If both adrenal insufficiency and hypothyroidism coexist, steroids must always be started before thyroid hormone replacement to avoid precipitating an adrenal crisis 3

Fasting and Dietary Preparation

Standard Fasting Requirements

• Minimum 4 hours fasting from solid foods and flavored beverages for procedures requiring [¹⁸F]FDG PET/CT scans 1
• Plain water only is permitted during fasting periods for [¹⁸F]FDG-PET/CT; no sugar-containing liquids 1
• Halt intravenous glucose solutions and parenteral nutrition at least 4 hours before [¹⁸F]FDG administration 1
• Avoid coffee or caffeinated beverages even if "sugarless," as they may contain traces of simple carbohydrates and cause excitant effects 1

Blood Glucose Management

• Ensure low blood glucose levels through at least 4 hours of fasting to minimize insulin-mediated glucose uptake by non-tumor cells 1
• Check serum glucose levels before [¹⁸F]FDG administration 1

Medication Management

Timing of Medication Adjustments

• Implement appropriate washout periods for disease-modifying therapies, particularly after long-acting lymphodepleting agents like alemtuzumab or cytotoxic treatments 1
• Balance washout duration to minimize disease relapse risk while avoiding complications from treatment sequences 1
• Maintain essential medications unless specifically contraindicated for the examination type 1

Specific Drug Considerations

• Insulin and insulin secretagogues may require dose reduction when combined with metformin to minimize hypoglycemia risk 2
• Anticoagulants and antiplatelet agents should be reviewed for bleeding risk during invasive procedures 1

Pre-Examination Laboratory Testing

Essential Baseline Tests

• Renal function assessment with eGFR measurement, particularly before contrast-enhanced studies 2
• Hematologic parameters including complete blood count to assess for anemia or other abnormalities 3
• Liver function tests in patients with known or suspected hepatic disease 2
• Pregnancy testing must be performed in all persons of reproductive capacity when doubt exists, using urine pregnancy test before radiopharmaceutical injection 1

Condition-Specific Testing

• Vitamin B12 levels should be measured at 2-3 year intervals in patients on long-term metformin therapy 2
• Thyroid function tests (TSH, free T4) for patients with fatigue, weight changes, or other thyroid-related symptoms 3
• Cardiac biomarkers if cardiovascular stress is anticipated 1

Physical Examination Requirements

Cardiovascular Assessment

• Electrocardiography and echocardiography are mandatory for patients undergoing procedures with cardiac risk 1
• Blood pressure measurement and assessment of hypertension control 1
• Evaluation for heart failure signs including peripheral edema and pulmonary congestion 2

Respiratory Evaluation

• Lung function testing with plain chest radiography as standard screening 1
• Additional respiratory work-up including chest CT and specialist referral for patients with abnormal lung function tests 1

Neurological Assessment

• Detailed neurological examination with disease history and disability status for patients with neurological conditions 1
• MRI examination when indicated by clinical findings 1

Patient Positioning and Comfort Measures

Positioning Protocols

• Supine position with arms alongside the body for whole-body imaging to enable complete examination 1
• Use support devices such as foam pallets for arms to reduce beam hardening artifacts on the spine 1
• Optimal patient positioning is mandatory for patients with bone disease to minimize discomfort 1

Comfort and Anxiety Management

• Inquire about claustrophobia when scheduling to facilitate premedication planning 1
• Analgesics may be used to relieve patient discomfort, particularly in those with bone disease 1
• Regular use of sedatives such as short-acting benzodiazepines is not recommended in adult patients 1
• Maintain warm room temperature during uptake phase to reduce brown fat activation in PET imaging 1

Hydration and Bladder Management

Hydration Protocols

• Adequate prehydration with 1 liter of water 2 hours prior to procedures involving contrast agents 1
• Oral hydration is generally sufficient, but IV hydration may be necessary for debilitated or fasting patients 1

Bladder Preparation

• Void immediately prior to PET/CT examination to reduce bladder activity and artifacts 1
• Bladder emptying is essential in diuretic renal scans to prevent slowed drainage and vesicoureteral reflux 1
• Avoid routine bladder catheterization due to infection risk and increased patient discomfort 1

Special Populations

Elderly Patients (Age ≥65 or ≥80)

• More frequent renal function assessment due to greater likelihood of hepatic, renal, or cardiac impairment 2
• Patients over 80 years should not take metformin unless kidneys have been checked and are normal 2
• Additional cardiological evaluation for those aged >40 years with cardiac risk factors 1

Pediatric Patients

• Age-appropriate preparation with discussions tailored to developmental level 1
• Caregiver presence should be encouraged to reassure the child and improve study outcomes 1
• Positive distractors such as favorite toys to comfort during procedures 1
• Maintain warm environment to reduce brown fat activation, which is very common in young patients 1

Critical Safety Considerations

Contraindications to Proceed

• Active neoplasia or myelodysplasia 1
• Acute or chronic uncontrolled infection 1
• Uncontrolled psychiatric disease or conditions raising risk of poor treatment adherence 1
• Severe renal impairment (eGFR <30 mL/min/1.73 m²) for metformin-treated patients 2

Emergency Preparedness

• Patients should be educated on symptoms requiring immediate medical attention, such as lactic acidosis symptoms in metformin users 2
• Emergency contact information should be provided for post-procedure complications 2
• Clear instructions on when to resume medications after procedures 2