Elevated level of serum cystatin-C concentration is a useful predictor for myelosuppression induced by methotrexate for treatment of rheumatoid arthritis

Methotrexate (MTX) is indispensable for the treatment of rheumatoid arthritis (RA). However, a small number of patients treated with MTX occasionally encounter some life-threatening events, including myelosuppression. Renal insufficiency, one of risk factors for these events, is difficult to assess because the serum creatinine concentration level and estimated glomerular filtration rate are sometimes inaccurately determined in aged RA patients. As a better indicator to evaluate this pathology, we measured the serum cystatin-C (Cys-C) level in 78 RA patients ≥50 years who were treated with MTX and observed for a year. The measurement achieved successful screening of two patients with leukocytopenia, one with interstitial lung disease (ILD), and two with liver dysfunction. An additional four referral inpatients with MTX-induced adverse events (three with pancytopenia, one with ILD) were enrolled for analysis, amounting to 82 patients. The logistic regression analysis showed that a correlation was observed between myelotoxicity and serum Cys-C level (elevation per 0.1 mg/dl; odds ratio 2.34, 95% confidence interval 1.08–5.09, p = 0.03). In conclusion, elderly RA patients potentially have subclinical renal insufficiency detected by the serum Cys-C concentration level. The elevated level of serum Cys-C is a more sensitive indicator to predict MTX-induced myelotoxicity than that of serum creatinine.