We focused on serum Alb and leukocyte subtype levels as prognostic factors for tacrolimus therapy outcome in UC. Regarding treatment effect prediction using Alb levels, the change in Alb level within 2 weeks of anti-TNFα treatment can predict the prognosis15. We previously analyzed this idea by applying it to tacrolimus therapy and reported that the ratio of Alb at 2 weeks after achieving a high tacrolimus trough to Alb before tacrolimus induction could predict failure within 3 months16. In our previous study, we performed the same analysis on CRP, Hb, and WBC, excluding fractions other than Alb, but only Alb showed significant results. In our previous study, only the ratios of week 2/week 0 and week 1/week 0 Alb were calculated, not the week 2/week 1 Alb ratios. In this study, we decided to include the week 2/week 1 Alb ratio. Interestingly, the week 2/week 1 Alb ratio was a more accurate prognostic factor by ROC analysis than the week 2/week 0 Alb ratio that was reported in our previous study16. This difference, as described in our previous report, occurred because serum Alb levels were enriched due to intravascular dehydration associated with frequent diarrhea and bloody stools before tacrolimus induction, but serum Alb levels decreased due to blood dilution by intravenous infusion at week 1. Additionally, there are some cases that do not show sufficient Alb elevation due to a tacrolimus refractory state, and we believe that the change in Alb between week 0 and week 1 was greater than that between week 0 and week 2.
As a novel approach in this study, the absolute counts, rate, and ratio of leukocyte subtypes before tacrolimus induction and at week 1 and week 2 were analyzed by comparing the failure and non-failure groups. From these analyses, the L/M ratio at week 1 most accurately predicted failure within 3 months. The L/M ratio has been reported to be a prognostic indicator in the field of malignancy, and a low L/M ratio has been shown to be a poor prognostic factor18. The usefulness of the L/M ratio as an activity index in UC was first reported by Cherfane et al., and a significant difference in the L/M ratio between active and quiescent UC groups (that correlated with clinical and endoscopic activity) was shown in their study19. In the report by Okba et al., the L/M ratio showed a significant difference between the inactive and active UC groups20. Xu et al. reported that the L/M ratio in patients with UC showed a significant difference between active and inactive groups as well as between active and inactive groups in a cohort of patients with Crohn’s disease21. As described above, the L/M ratio has been shown to be useful in assessing UC activity, and all these reports have shown that a low L/M ratio is indicative of active UC19,20,21. Previous studies of UC and Crohn’s disease have shown reduced lymphocyte reactivity at the peripheral and mucosal levels, and lymphocyte reduction can occur with inflammation22,23,24. Monocytes differentiate into macrophages and dendritic cells in tissues during inflammation and play a role in innate immunity. The sustained activation of monocytes and incomplete innate immune responses can be involved in IBD development25. Furthermore, monocyte hyperplasia increased the risk for worse clinical outcomes in IBD26. The L/M ratio is a value that indicates UC activity, and it is believed to predict failure by the same mechanism as the aforementioned biomarkers. Furthermore, the reason the L/M ratio predicted failure at week 1, not at week 0 (before tacrolimus induction), in the present study was that most patients were equally active before tacrolimus induction; therefore, there were no significant differences in the L/M ratios between the failure and non-failure groups at that time. However, the L/M ratios of the non-failure group, who improved with tacrolimus treatment, increased in one week.
Nishida et al. performed a leukocyte subtype analysis similar to that conducted in our study and reported that the N/L ratio before tacrolimus induction could be a predictor of the therapeutic effect of tacrolimus17. In the present study, the N/L ratio before tacrolimus induction was not significantly different between the failure and non-failure groups. This difference may be because the endpoint of our study was set at 3 months while Nishida et al. did not define an endpoint. In addition, the small sample sizes in both studies may have caused the differences in data.
We further analyzed the combination of week 2/week 1 Alb and week 1 L/M ratios. Such an analysis—using a combination of two markers—has been conducted in studies on relapse prediction using multiple biomarkers; this analysis is especially seen in studies incorporating FC and FIT. These studies showed that patients with UC in clinical remission who were positive for both FC and FIT had a higher rate of subsequent relapse, demonstrating the usefulness of a combined analysis of markers27,28. In this study, the combination of the week 2/week 1 Alb ratio and L/M ratio at week 1 showed a more accurate failure rate.
We focused not only on the values before induction but also on the values and their changes after induction. Although it would be ideal to have a test that can predict the effect of UC treatment before induction (and there are reports of such a test), there is no test that can predict prognosis with certainty17,29,30. Another advantage of the evaluation method suggested in this study is that the examined Alb and leukocyte subtypes can be easily and inexpensively measured at any institution.
This study had several limitations. First, it was a single-center, retrospective study with a small sample size. Second, the examined markers have not been compared with other biomarkers. Although it was established that these biomarkers could predict the prognosis of UC, a comparison with various biomarkers will need to be conducted in our future studies. Furthermore, in this study, it took a median of 4 days from tacrolimus induction to achieve a high trough, and it took approximately 18 days from tacrolimus induction to determine both the week 2/week 1 Alb ratio and the L/M ratio at week 1; it may not be realistic to start considering the next treatment at this point. We hope that these markers will be considered as decision-making factors for tacrolimus therapy for UC16.
In conclusion, a low week 2/week 1 Alb ratio and a low L/M ratio at week 1 were predictive of failure of tacrolimus-based therapy for UC in this study. The combination of these markers can provide a more accurate prognosis.