What labs are included in the workup for psoriasis?

Laboratory Workup for Psoriasis

The standard laboratory workup for psoriasis should include a complete blood count, liver function tests, renal function tests, hepatitis panel, and tuberculosis testing before initiating systemic therapy. 1, 2

Initial Laboratory Assessment

For All Psoriasis Patients:

• Complete history and physical examination with specific attention to:
  • Extent of skin involvement
  • Presence of joint symptoms (psoriatic arthritis)
  • Previous treatments and responses
  • Comorbid conditions

Basic Laboratory Tests:

• Complete Blood Count (CBC) including platelet count
• Chemistry screen with liver function tests
• Serum creatinine and BUN (renal function)
• Serum lipid profile
• Serum magnesium, potassium, uric acid

Additional Testing Based on Treatment Plan

For Patients Considering Methotrexate:

• Liver function tests (AST, ALT, alkaline phosphatase, bilirubin)
• Complete blood count with differential
• Serum creatinine
• Hepatitis B and C panel
• Consider liver biopsy before starting or continuing methotrexate in high-risk patients 1, 3

For Patients Considering Cyclosporine:

• Blood pressure measurements (on at least two occasions)
• Serum creatinine (on two occasions)
• BUN
• Serum magnesium, potassium, uric acid
• Lipid profile 1, 4

For Patients Considering Biologics:

• Tuberculosis testing (tuberculin skin test or interferon-gamma release assay) - strongest evidence (grade B) 1, 5, 6
• Hepatitis B and C panel
• Complete blood count
• Chemistry screen with liver function tests 1, 5

Specific Biologic Monitoring:

• Alefacept: CD4 counts approximately every 2 weeks
• Efalizumab: More frequent platelet count monitoring
• Infliximab: More frequent liver function tests
• TNF blockers: More frequent tuberculosis testing 5

Monitoring Schedule

Methotrexate Monitoring:

• Initial phase: Weekly CBC, liver function tests, serum creatinine for first 2-4 weeks
• Maintenance phase: Every 1-2 months for stable patients 1, 3
• Consider liver biopsy after 1.5g cumulative dose 1

Cyclosporine Monitoring:

• Initial phase: Blood pressure and serum creatinine every 2 weeks for first 3 months
• Maintenance phase: Monthly monitoring if stable
• Additional tests: CBC, uric acid, potassium, lipids, and magnesium every 2 weeks for first 3 months, then monthly 1, 4

Biologics Monitoring:

• Less intensive laboratory monitoring is required compared to traditional systemic agents
• Monitoring practices should be tailored to the specific biologic agent 7, 5, 6

Common Pitfalls to Avoid

1. Failing to screen for tuberculosis before starting biologics or TNF inhibitors
2. Not recognizing drug interactions with methotrexate (alcohol, salicylates, NSAIDs, co-trimoxazole, trimethoprim, probenecid, phenytoin, retinoids)
3. Inadequate contraception counseling for patients on teratogenic medications (methotrexate, acitretin)
4. Overlooking vaccination status - live vaccines should be avoided during biologic therapy
5. Excessive laboratory monitoring for biologics without evidence-based justification 7, 6

Special Considerations

• Pregnancy planning: Women should avoid conception during treatment with methotrexate and for at least one menstrual cycle after stopping; for acitretin, contraception is needed for 3 years after discontinuation 1
• Male fertility: Methotrexate causes sperm abnormalities and is contraindicated for men wishing to father children 1
• Elderly patients: Consider lower starting doses and more frequent monitoring of renal function 1

Laboratory monitoring should be adjusted based on the specific treatment regimen, patient comorbidities, and clinical response to therapy.