Long-Term Routine Laboratory Toxicity Monitoring of Immunomodulatory Drugs in Rheumatoid Arthritis : A Retrospective...

Area of Science:

• Rheumatology
• Clinical Pharmacology
• Laboratory Medicine

Background:

• Limited data exists on the value of long-term routine laboratory toxicity monitoring (lt-RLTM) during disease-modifying antirheumatic drug (DMARD) use.
• This scarcity leads to frequent monitoring in clinical practice, potentially without clear benefit.

Purpose of the Study:

• To determine the cumulative incidence of abnormal and very abnormal laboratory monitoring results in rheumatoid arthritis (RA) patients.
• To characterize the clinical context surrounding new very abnormal laboratory results during DMARD therapy.

Main Methods:

• Retrospective cohort study conducted in the Netherlands from July 2008 to April 2020.
• Analysis of lt-RLTM data from 4774 RA patients on DMARDs for at least 6 months.
• Calculation of cumulative probabilities for abnormal/very abnormal results in liver function, kidney function (eGFR), hemoglobin, leukocyte, and platelet counts; chart review for clinical context of new very abnormal results.

Main Results:

• Cumulative probabilities of very abnormal results at 5 years ranged from 0.3% (leukocyte count) to 11% (eGFR).
• New very abnormal results (n=449) were often anticipated, unrelated to DMARDs, or did not prompt action.
• High cumulative incidence of less serious abnormal results observed, e.g., 39% for eGFR <60 mL/min/1.73 m² and 61% for Hb <7.5/8 mmol/L.

Conclusions:

• Most very abnormal laboratory results during long-term monitoring were clinically anticipated or occurred post-dose escalation.
• The cumulative incidence of less serious abnormal results was notably high.
• Current strategies for lt-RLTM warrant reconsideration due to findings on the clinical utility of frequent monitoring.