Impact of Six-Month Monitoring Compared to Three-Month Monitoring of Laboratories During Methotrexate Therapy.

OBJECTIVE

To evaluate whether extending the American College of Rheumatology-recommended monitoring interval for complete blood count and liver function tests in patients receiving methotrexate (MTX) affects timely detection of medication-related toxicity.

METHODS

We conducted an observational cohort analysis of 14,199 laboratory encounters from 2,439 patients receiving MTX with at least two measurements of alanine aminotransferase (ALT), aspartate aminotransferase (AST), white blood cell (WBC) count, hematocrit (HCT), mean corpuscular volume (MCV), and/or platelet (PLT) count. Fibrosis-4 (FIB-4) scores were calculated when possible. Changes between consecutive measurements were plotted against time between encounters. Monitoring intervals of three months (45-135 days) and six months (135-225 days) were compared. After propensity score matching, we assessed incident clinically relevant abnormalities.

RESULTS

Testing frequency showed no meaningful correlation with changes in ALT, AST, WBC, HCT, MCV, PLT, or FIB-4 (all R2 < 0.01). Mean laboratory changes did not differ meaningfully between monitoring intervals. Patients monitored every 135 to 225 days were equally or less likely to develop incident abnormal results than those monitored every 45 to 135 days; most odds ratios (ORs) were not statistically significant (P > 0.05). Patients in the six-month group were less likely to develop ALT >1× upper limit of normal (OR 0.72 [95% confidence interval (CI) 0.52-0.99]) or MCV >100 fL (OR 0.67 [95% CI 0.46-0.96]).

CONCLUSION

Extending routine MTX monitoring from every three months to every six months was not associated with more severe abnormalities or delayed detection of toxicity, suggesting quarterly testing may be more frequent than necessary and could be reconsidered to reduce cost and patient burden.