EASIX and sC5b-9 Levels Predict TA-TMA Risk After Allo-HCT in Adults

• Baseline EASIX and day 14 sC5b-9 levels were independently associated with risk of transplant-associated thrombotic microangiopathy (TA-TMA) after allogeneic hematopoietic cell transplantation (allo-HCT).

• Combining the two biomarkers stratified patients into low-, intermediate-, and high-risk groups, with 100-day TA-TMA incidences of 2.2%, 7.1%, and 32.4%, respectively.

• The risk stratification system showed moderate discrimination (time-dependent AUC 0.75, 95% CI 0.66–0.84).

• External validation and standardized assays are needed before clinical implementation.

Why This Study Matters

Transplant-associated thrombotic microangiopathy (TA-TMA) is a life-threatening complication of allogeneic hematopoietic cell transplantation (allo-HCT), often leading to multi-organ failure and death if not recognized and treated early. Despite advances in supportive care, predicting which patients will develop TA-TMA remains a clinical challenge, especially in adult populations. Currently, no validated biomarkers are widely used to identify high-risk patients at the time of transplantation or shortly afterward. The combination of baseline endothelial activation and stress index (EASIX) and soluble C5b-9 (sC5b-9)—a terminal complement activation product—may offer a practical risk stratification tool to guide monitoring and early intervention.

How the Study Was Conducted

In this prospective observational study conducted at a single center (presumed), investigators consecutively enrolled adults over the age of 14 years undergoing allo-HCT. TA-TMA was screened and diagnosed using the standardized harmonization criteria. Blood samples were collected at baseline for EASIX calculation—a composite score derived from platelet count, creatinine, and lactate dehydrogenase—and at day 14 for sC5b-9 levels. The primary endpoint was the cumulative incidence of TA-TMA within 100 days post-transplant. Researchers performed multivariable Cox regression analyses to evaluate associations with TA-TMA and used time-dependent receiver operating characteristic (ROC) curves to assess discriminatory performance.

What the Researchers Found

Among the consecutive cohort, the 100-day cumulative incidence of TA-TMA was 6.5% (95% CI 4.5–8.9%). Two biomarkers emerged as independent predictors in multivariable analysis: baseline EASIX (hazard ratio [HR] 1.33, p = 0.011) and day 14 sC5b-9 level (HR 2.84, p < 0.001). Optimal cutoffs were an EASIX value of 6.2 and an sC5b-9 concentration of 217 ng/mL.

Using these cutoffs, patients were stratified into three risk groups: low risk (neither marker elevated), intermediate risk (one marker elevated), and high risk (both markers elevated). The corresponding 100-day TA-TMA incidences were 2.2%, 7.1%, and 32.4%. Compared with the low-risk group, the intermediate-risk group had a HR of 3.29 (95% CI 1.39–7.79), and the high-risk group had a HR of 14.32 (95% CI 5.62–36.50). The combined stratification demonstrated moderate discrimination, with a time-dependent area under the curve (AUC) of 0.75 (95% CI 0.66–0.84).

What the Findings May Mean

The results suggest that a simple combination of a baseline clinical score (EASIX) and a single post-transplant complement marker (sC5b-9) can identify adult allo-HCT recipients at substantially different risk for TA-TMA. The nearly 15-fold increase in risk for the high-risk group compared with low-risk patients underscores the potential of this approach for early risk-adapted monitoring and preemptive management. However, because the study is observational and the discrimination was only moderate, the findings should be considered hypothesis-generating. Prospective validation in independent, multicenter cohorts is essential before the stratification can be recommended for routine use. Additionally, the sC5b-9 threshold of 217 ng/mL needs to be validated with standardized assays.

Strengths and Limitations

The study’s strengths include its prospective design, use of harmonized diagnostic criteria for TA-TMA, and the a priori selection of clinically accessible biomarkers. The time-dependent AUC analysis accounts for the competing risk of death and provides a realistic measure of predictive performance.

Important limitations include the lack of reported total sample size and number of events (beyond incidence), which precludes assessment of model stability. The study was likely conducted at a single center, raising concerns about generalizability to other patient populations and transplant protocols. Residual confounding cannot be excluded, and the moderate AUC (0.75) indicates that the stratification does not perfectly separate risk groups. External validation and calibration in larger, diverse cohorts are necessary before the model can be used to guide clinical decisions.

Implications for Practice and Research

If validated, this dual-marker approach could enable clinicians to identify high-risk patients early—within the first two weeks after allo-HCT—and intensify surveillance for signs of microangiopathy or consider prophylactic strategies such as complement inhibition. The tools are already available in many clinical laboratories, since EASIX relies on standard complete blood count and chemistry panels, and sC5b-9 assays are increasingly accessible. Further research should focus on confirming these cutoffs, assessing the impact of risk-stratified monitoring on outcomes, and determining whether intervention guided by these markers improves prognosis without increasing toxicity.

Funding, Disclosures, and Registration

The study was registered at ClinicalTrials.gov under identifier NCT06102694. The source material does not specify funding sources or author disclosures; no information on conflicts of interest was available.

References

Guo W, Chen S, Zhang X, et al. EASIX and sC5b-9 for early identification of adults at high risk of developing TA-TMA after allo-HCT. Bone Marrow Transplantation. 2026 Jul 24. PMID: 42493573. https://pubmed.ncbi.nlm.nih.gov/42493573/