What labs should I draw for a patient with ongoing pain on their current medication regimen?

Laboratory Tests for Patients with Ongoing Pain on Current Medication Regimen

For patients with ongoing pain on their current medication regimen, a comprehensive panel of laboratory tests should include urine drug testing, complete blood count, comprehensive metabolic panel, and medication-specific monitoring to ensure safety and efficacy of treatment.

Core Laboratory Tests

Urine Drug Testing

• Perform urine drug testing before starting opioid therapy and at least annually to assess for prescribed medications, other controlled substances, and illicit drugs 1
• Urine drug testing helps identify unreported drug use and confirms patient adherence to prescribed medications 1
• Standardized clinic policies regarding urine drug testing help destigmatize its use 1

Complete Blood Count (CBC)

• CBC provides information about oxygen-carrying capacity and immune system function 2
• Helps identify potential side effects of medications, including bone marrow suppression 2
• Monitors for anemia which may contribute to fatigue and decreased function in chronic pain patients 2

Comprehensive Metabolic Panel

• Assess liver function through ALT, AST, alkaline phosphatase, and bilirubin to monitor for medication-induced hepatotoxicity 3
• Evaluate kidney function through BUN and creatinine, especially important for patients on NSAIDs or certain adjuvant medications 3
• Monitor electrolytes which may be affected by medication side effects (e.g., hyponatremia with certain antidepressants) 3

Medication-Specific Monitoring

For Opioid Therapy

• Consider blood testing to document opioid tolerance and evaluate patient compliance 4
• Calculate total morphine milligram equivalents (MME) per day to assess overdose risk 1
• Monitor for signs of respiratory depression, especially with concurrent benzodiazepine use 1

For Adjuvant Analgesics

• For anticonvulsants (gabapentin, pregabalin, carbamazepine):
  • Monitor complete blood count for potential hematologic abnormalities 1
  • For carbamazepine specifically, check serum sodium levels to monitor for hyponatremia 1

For NSAIDs

• Monitor renal function regularly as NSAIDs can cause acute kidney injury 5
• Check for gastrointestinal bleeding through hemoglobin/hematocrit levels 5
• Consider COX-2 selective NSAIDs to reduce GI side effects in high-risk patients 5

Frequency of Testing

• Initial baseline laboratory testing before starting pain medications 1
• For patients on stable doses of opioids, perform urine drug testing at least annually 1
• More frequent monitoring (every 3-6 months) for patients on high-dose opioids or with risk factors 1
• Assess pain relief and functional improvement after 1-2 weeks of therapy changes 5

Special Considerations

• For elderly patients, more frequent monitoring may be necessary due to age-related changes in pharmacokinetics and pharmacodynamics 1
• Patients with multiple medications require careful monitoring for drug interactions 5
• Consider more frequent testing in patients with history of substance use disorder 1

Interpretation of Results

• Abnormal results should prompt reevaluation of the pain management strategy 1
• Negative drug tests for prescribed opioids may indicate non-adherence but consider other possible explanations 1
• Do not dismiss patients from practice based solely on unexpected drug test results 1
• Use test results as an opportunity to improve patient education and safety 1

Documentation

• Document all laboratory test results and their interpretation in the patient's medical record 1
• Include rationale for medication changes based on laboratory findings 1
• Provide patients with written follow-up pain plans, including prescribed medications 1