What blood tests are required before starting Plaquenil (hydroxychloroquine)?

Blood Tests Required Before Starting Plaquenil (Hydroxychloroquine)

Before starting hydroxychloroquine (Plaquenil), a complete blood count (CBC) and liver function tests (LFTs) are recommended as baseline laboratory tests. 1

Required Baseline Laboratory Testing

Essential Tests:

• Complete Blood Count (CBC)

  • Monitors for potential hematologic effects
  • Screens for pre-existing cytopenias

• Liver Function Tests (LFTs)

  • Assesses baseline liver function
  • Helps monitor for potential hepatotoxicity

Additional Baseline Tests to Consider:

• Renal Function Tests

  • Particularly important in patients with pre-existing kidney disease
  • Dose adjustment may be needed in severe renal impairment 2

• G6PD Level

  • Consider in patients with risk factors for G6PD deficiency
  • Hydroxychloroquine can cause hemolytic anemia in G6PD-deficient patients 2, 3

• ECG

  • Consider in patients with cardiac risk factors
  • Screens for pre-existing conduction abnormalities 2

Non-Laboratory Baseline Assessment

• Baseline Ocular Examination
  • Essential before starting hydroxychloroquine 1, 2, 3
  • Should include:
    • Best corrected visual acuity
    • Automated threshold visual field of central 10 degrees (24 degrees for Asian patients)
    • Spectral domain optical coherence tomography (SD-OCT) 3
  • Treatment does not need to be delayed for initial retinal screening 1

Ongoing Monitoring

After initiating hydroxychloroquine, the American College of Rheumatology recommends:

• Laboratory Monitoring

  • CBC and LFTs annually 1
  • More frequent monitoring may be needed in patients with risk factors

• Ophthalmologic Monitoring

  • Annual retinal screening for pediatric patients 1
  • For adults: baseline exam, then annual exams starting after 5 years of treatment for low-risk patients 1, 2
  • More frequent monitoring (annual from the start) for high-risk patients 2

Risk Factors Requiring More Vigilant Monitoring

• Daily dose >5 mg/kg of actual body weight
• Treatment duration >5 years
• Renal impairment
• Concomitant hepatotoxic drugs
• Age >65 years
• Pre-existing retinal or macular disease 2

Common Pitfalls to Avoid

1. Overlooking baseline ophthalmologic examination

   • Retinal toxicity is a serious concern with hydroxychloroquine
   • Early detection through proper screening is essential 4

2. Inadequate weight-based dosing

   • Doses should not exceed 5 mg/kg/day of actual body weight to minimize retinal toxicity risk 2

3. Neglecting annual monitoring

   • Even with normal baseline tests, annual monitoring is important for early detection of toxicity 1

4. Failure to recognize early signs of toxicity

   • Reduced retinal sensitivity can occur before clinical evidence of retinopathy 5
   • Regular monitoring helps detect changes before permanent damage occurs

By following these guidelines for baseline testing and ongoing monitoring, clinicians can help minimize the risk of adverse effects while maximizing the therapeutic benefits of hydroxychloroquine therapy.