What laboratory tests are used to diagnose Psoriasis?

From the Guidelines

Patients with psoriasis should undergo laboratory tests including a complete blood count (CBC), comprehensive metabolic panel (CMP), lipid panel, and inflammatory markers like C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) to establish baseline health status and identify comorbidities before starting treatment. These tests are essential because psoriasis is a systemic inflammatory condition that increases risk for metabolic syndrome, cardiovascular disease, and other inflammatory conditions 1. For patients on systemic medications, specific monitoring is required:

• Methotrexate necessitates liver function tests (LFTs), CBC, and renal function tests every 1-3 months, with closer monitoring in patients with risk factors such as renal insufficiency or advanced age 1
• Biologics require tuberculosis screening (QuantiFERON-TB Gold or PPD skin test) before initiation 1
• Cyclosporine requires blood pressure monitoring and renal function tests Additionally, HLA-B27 testing may be useful in cases with joint involvement to identify psoriatic arthritis. Regular monitoring is crucial for safe, effective treatment, and patients with moderate to severe disease should have these tests performed at diagnosis and periodically during treatment to ensure medication safety and monitor for associated conditions. Key laboratory tests to consider include:
• Chemistry screen with liver function tests
• Complete blood cell count including platelet count
• Hepatitis panel
• Tuberculosis (TB) testing These tests help identify potential comorbidities and monitor for medication-related adverse effects, allowing for timely interventions to improve patient outcomes and quality of life.

From the Research

Psoriasis Labs and Systemic Therapy

• Psoriasis is a systemic inflammatory disease associated with increased risk of comorbidities, such as psoriatic arthritis, Crohn's disease, malignancy, obesity, and cardiovascular diseases 2.
• The decision to use one therapy over another is impacted by these comorbidities, and treatment regimens should be tailored to meet the specific needs based on disease severity, quality of life, response to previous therapies, and presence of comorbidities 2.
• Systemic therapies, including conventional and newer oral systemic agents and biologics, are available for patients with moderate-to-severe psoriasis, and each option presents a unique set of benefits, safety risks, dosing schedules, and monitoring requirements 3.

Monitoring Liver Function

• Methotrexate is a widely used and efficacious treatment for psoriasis, but current recommendations advise liver biopsy after each cumulative 1-1.5g dosage of methotrexate 4.
• However, studies suggest that in patients with no risk factors for liver disease on long-term, low-dosage methotrexate, liver biopsy may be justified after an initial cumulative dosage of 4g 4.
• Advances in non-invasive assessment of liver fibrogenesis may eventually further reduce the need for biopsy 4.

Evidence-Based Updates on Systemic Therapies

• A systematic review of the literature found that biologic agents, including anti-interleukin (IL)-17 agents, are effective in treating psoriasis, with infliximab consistently superior to others and etanercept the least effective of the tumor necrosis factor-alpha inhibitors 5.
• Newer oral agents are being studied and may be an option as an alternative to traditional oral agents, with more favorable safety profiles 5.
• Current studies continue to support the use of biologic agents in the treatment of moderate to severe psoriasis, with better efficacy and safety profiles than traditional systemic agents 5.

Baseline Pathological Liver Function Tests

• A real-world analysis found that baseline pathological liver function tests in patients with psoriasis support the indication for systemic therapy rather than being a reason against it 6.
• The study found that patients with elevated liver function tests (LFTs) at baseline had a higher mean Psoriasis Area and Severity Index (PASI) and were more likely to be male, with a higher prevalence of metabolic syndrome comorbidities 6.
• During the follow-up period, LFTs decreased significantly over time in the group of patients with initially elevated LFTs, whereas Fibrosis-4 scores demonstrated no significant change 6.