What laboratory tests should be obtained and monitored when initiating and continuing methotrexate therapy, including baseline tests, follow‑up intervals, and thresholds for dose adjustment or discontinuation?

Laboratory Monitoring for Methotrexate Therapy

All patients receiving methotrexate require baseline complete blood count with differential, liver function tests (AST, ALT, albumin, bilirubin), and renal function tests (creatinine, eGFR) before initiation, followed by monitoring at weeks 2,4,8, and 12, then every 3–4 months for stable patients. 1

Baseline Testing (Before Starting Methotrexate)

Mandatory baseline tests include: 1, 2

• Complete blood count with differential and platelet count 1, 2
• Liver function tests: AST, ALT, alkaline phosphatase, albumin, bilirubin 1, 3
• Renal function: serum creatinine and eGFR 1, 3
• Chest X-ray to establish baseline pulmonary status 1
• Pregnancy test in all women of childbearing potential 1
• Hepatitis B and C serologic screening in patients with risk factors (history of excessive alcohol consumption, persistently abnormal baseline liver tests, or chronic hepatitis B or C infection) 1, 3

Baseline liver biopsy is NOT recommended, regardless of risk factors. 1, 2 However, for patients with high-risk features (BMI >28 kg/m² or alcohol intake >14 drinks/week), add non-invasive liver fibrosis assessment using FIB-4 Index or transient elastography (FibroScan). 1

Initial Monitoring Schedule (First 3 Months)

The most intensive monitoring occurs during the first 3 months: 1

• Check CBC, liver enzymes (AST, ALT, albumin), and renal function at weeks 2,4,8, and 12 after the first dose 1
• Increase monitoring frequency to every 2–4 weeks during dose escalation or when risk factors are present 1
• The American College of Rheumatology guidelines for juvenile idiopathic arthritis recommend laboratory measurements approximately 1 month after initiating methotrexate and then approximately 1–2 months after any subsequent increase in methotrexate dose 4

Critical timing consideration: Obtain laboratory measurements 1–2 days prior to the scheduled weekly dose of methotrexate, not within 2 days after dosing, as transient elevations may occur. 4, 1

Maintenance Monitoring (Stable Patients)

For patients on stable doses with no recent abnormalities: 1, 3

• Continue CBC, liver enzymes, and renal function testing every 3–4 months 4, 1
• The American College of Rheumatology recommends monitoring at 4–8 week intervals for rheumatoid arthritis patients 3
• More frequent monitoring (every 1–2 months) may be indicated during periods of increased risk, such as dehydration or concurrent illness 2

Specific Parameters and Thresholds for Action

Hematologic Toxicity Management

Discontinue methotrexate immediately if any of the following occur: 1, 5, 2

• White blood cell count <3.0 × 10⁹/L 1
• Absolute neutrophil count <1.0 × 10⁹/L 1, 5
• Platelet count <100 × 10⁹/L (or <100,000/mm³) 1, 2
• Hemoglobin drop >2 g/L from prior value 1

For moderate hematologic abnormalities: 5

• Mild thrombocytopenia (100,000–150,000/mm³): increase monitoring frequency to every 2–4 weeks 1
• Moderate neutropenia (500–1,000/mm³): withhold methotrexate temporarily and increase monitoring to weekly 5
• Severe neutropenia (<500/mm³): discontinue methotrexate immediately and initiate leucovorin rescue therapy; consider G-CSF (filgrastim 5 μg/kg daily subcutaneously) 5

Hepatotoxicity Management

The American College of Rheumatology provides clear thresholds for liver enzyme elevations: 4, 1

• AST/ALT ≤2× upper limit of normal: Either no specific action or recheck at shorter interval 4
• AST/ALT >2× upper limit of normal: Decrease methotrexate dose or temporarily withhold administration 4, 1
• AST/ALT >3× upper limit of normal: If elevation persists after dose reduction, discontinue methotrexate 4

Additional hepatotoxicity monitoring criteria: 3

• Perform liver biopsy if persistent abnormalities develop, defined as elevations in AST in 5 of 9 determinations within a 12-month interval (or 6 of 12 if tests performed monthly) 3
• Perform liver biopsy if serum albumin decreases below the normal range in the setting of well-controlled disease 3
• For psoriasis patients, measure serum PIIINP (procollagen III N-terminal peptide) at least every 3 months; refer for specialist assessment if PIIINP >8 mg/L on two occasions, >4.2 mg/L on three measurements within 12 months, or >10 mg/L on a single measurement 1

Pretreatment liver biopsy should be performed only for patients with: 3

• History of prior excessive alcohol consumption
• Persistently abnormal baseline AST values
• Chronic hepatitis B or C infection

Renal Toxicity Monitoring

Measure serum creatinine and eGFR every 2–3 months to detect renal impairment. 1 Renal insufficiency is a critical risk factor for methotrexate toxicity because 85% of the drug is renally excreted. 6 Patients with impaired renal function require enhanced monitoring, lower thresholds for intervention, and consideration of dose reduction or discontinuation. 1, 6

Pulmonary Toxicity Surveillance

At every clinic visit, ask patients about dyspnea, dry cough, or fever. 1, 6 Obtain a chest X-ray and consider further work-up or referral if any respiratory symptoms are present, if the patient is >40 years old and a smoker, or if underlying lung disease exists. 1 Pulmonary toxicity typically presents as acute interstitial pneumonitis, is unrelated to cumulative dose, and is usually reversible after drug withdrawal. 1

Essential Preventive Measures

Mandatory folic acid supplementation: All patients on methotrexate must receive folic acid 1–5 mg daily (except on the day of methotrexate administration) or 5 mg weekly to reduce gastrointestinal, hepatic, and hematologic toxicity. 1, 6, 5 This supplementation is non-negotiable and significantly reduces adverse events. 1

High-Risk Populations Requiring Enhanced Monitoring

Patients with the following risk factors require more frequent monitoring (every 2–4 weeks initially): 1, 6

• Advanced age (>50–70 years) 6
• Renal insufficiency or decreased creatinine clearance 1, 6
• Obesity (BMI >28 kg/m²) 1
• Diabetes mellitus 1, 2
• History of excessive alcohol consumption 1, 2, 3
• Pre-existing liver disease 1, 2
• Hypoalbuminemia 6
• Concurrent use of NSAIDs, trimethoprim-sulfamethoxazole, or penicillins 1, 6

Common Pitfalls to Avoid

Do not obtain liver function tests within 2 days after methotrexate administration, as transient elevations may occur and lead to unnecessary interventions. 4, 1 Instead, draw labs 1–2 days before the scheduled weekly dose. 4

Do not perform routine surveillance liver biopsies in rheumatoid arthritis or psoriasis patients receiving traditional doses of methotrexate, as this practice is no longer recommended due to lack of benefit and procedural risk. 1, 3

Do not delay leucovorin administration if significant toxicity is suspected; early treatment is critical and efficacy diminishes dramatically after 24 hours. 5

Do not underestimate the severity of methotrexate-induced myelosuppression, as it accounts for the majority of methotrexate-associated fatalities (67 of 164 reported cases). 6 Patients with profound granulocytopenia and fever require immediate evaluation and usually need parenteral broad-spectrum antibiotic therapy. 2