Cystatin C Discrepancy Predicts Kidney Injury and Death in Cell Therapy

Refining Renal Risk Assessment in Cellular Therapy

Allogeneic hematopoietic stem cell transplantation and chimeric antigen receptor T-cell therapies offer curative potential for advanced hematologic malignancies, yet they carry substantial risks of treatment-related mortality [1, 2]. Acute kidney injury remains a frequent and severe complication in this population, often exacerbated by conditioning regimens, sepsis, and the nephrotoxic burden of antimicrobial prophylaxis [3, 4]. While clinicians routinely use estimated glomerular filtration rates to gauge renal reserve, these calculations can be misleading in patients with significant frailty or sarcopenia (the loss of skeletal muscle mass and strength often seen in chronic illness) [5, 6]. Standard creatinine-based assessments may fail to capture the true physiological vulnerability of patients who have endured multiple lines of prior therapy [7]. A multi-center study now examines whether the discordance between different filtration markers can provide a more precise prognostic window into post-transplant outcomes.

Defining the Discordance Gap

The researchers conducted a multicenter study focusing on adults undergoing either allogeneic hematopoietic stem cell transplant (HSCT) or adoptive T-cell therapies. To evaluate renal reserve before treatment, the team analyzed paired laboratory values of serum creatinine and cystatin C, a protein produced by all nucleated cells that serves as an alternative filtration marker. Unlike creatinine, which is a byproduct of muscle metabolism and fluctuates based on a patient's muscle mass, cystatin C provides a more stable reflection of glomerular function in patients with varying body compositions. These measurements were obtained within the 30 days preceding conditioning or lymphodepleting chemotherapy, ensuring the baseline reflected the patient's physiological status immediately prior to the high-intensity phase of treatment.

The central exposure of interest was eGFR discordance, a metric designed to identify patients whose renal function might be overestimated by standard creatinine-based formulas. The researchers defined this discordance as an estimated glomerular filtration rate based on cystatin C (eGFR cys) that was 30% or more lower than the estimated glomerular filtration rate based on serum creatinine (eGFR cr). This specific threshold identifies a significant gap where cystatin C suggests substantially lower filtration capacity than creatinine. This often occurs in patients with reduced muscle mass or chronic illness whose creatinine levels appear deceptively normal because they produce less metabolic waste, potentially masking underlying renal impairment.

To assess the clinical impact of this discrepancy, the study tracked a primary composite outcome of acute kidney injury (AKI) or death within 90 days following the HSCT or adoptive T-cell infusion. The researchers utilized a rigorous definition for AKI, requiring either a 50% or greater increase in serum creatinine from baseline or the receipt of kidney replacement therapy. By combining these renal events with all-cause mortality, the study aimed to determine if the pre-treatment gap between filtration markers could serve as a reliable prognostic indicator for the most severe early complications of cellular therapy.

Cohort Characteristics and Prevalence

The multicenter study evaluated two distinct patient populations undergoing intensive cellular therapies to determine the prevalence of renal filtration discrepancies. The first group consisted of 274 patients receiving allogeneic hematopoietic stem cell transplant (HSCT). This cohort had a median age of 65 years, with an interquartile range (IQR) of 52 to 71 years. Within this transplant group, 43% of the patients were female. When the researchers applied the criteria for estimated glomerular filtration rate (eGFR) discordance, they found that 86 patients (31%) met the definition of having a cystatin C-based filtration estimate at least 30% lower than their creatinine-based estimate. This high prevalence suggests that nearly one in three transplant candidates may have unrecognized renal vulnerability despite seemingly stable creatinine levels.

The second group comprised 236 adoptive T-cell recipients, a population with a slightly higher median age of 67 years (IQR 60 to 74). In contrast to the transplant cohort, the majority of these patients, 59%, were female. The prevalence of renal filtration discrepancy was similarly high in this group, as 78 patients (33%) exhibited eGFR discordance. These demographic and clinical data points underscore that a significant portion of patients across both treatment modalities enter the conditioning phase with a substantial gap between their two primary markers of kidney function. For the practicing clinician, these figures highlight that the 30% discordance threshold is not a rare laboratory anomaly but a common finding in the older, often sarcopenic population typically referred for advanced cell-based therapies.

Impact on Survival and Renal Function

The presence of a significant gap between filtration estimates carries heavy clinical weight for patients undergoing intensive cellular therapies. In the cohort of patients receiving hematopoietic stem cell transplant, eGFR discordance was associated with 1.75 times higher odds of experiencing acute kidney injury or death within 90 days (odds ratio [OR] 1.75; 95% confidence interval [CI] 1.03 to 3.02). This composite outcome included either a 50% or greater increase in serum creatinine, the initiation of kidney replacement therapy, or mortality. The risk was even more pronounced among adoptive T-cell recipients, where eGFR discordance was associated with more than double the odds of acute kidney injury or death (OR 2.37; 95% CI 1.12 to 4.94). These findings suggest that relying solely on creatinine-based estimates may lead clinicians to underestimate the risk of severe post-treatment complications and early mortality in approximately one-third of their patients.

To ensure the robustness of these associations, the researchers employed rigorous statistical frameworks to account for potential biases. The study utilized multivariable logistic regression and cause-specific Cox regression, incorporating inverse probability weighting (a statistical method used to adjust for confounders by weighting individuals to create a synthetic sample where treatment or exposure is independent of measured baseline characteristics). This approach allowed the authors to isolate the impact of the filtration discrepancy from other clinical variables. Beyond the primary composite outcome, the researchers also observed that this renal discordance correlated with other markers of poor recovery, specifically a slower time to platelet engraftment in transplant patients and prolonged cytopenia (a sustained reduction in blood cell counts) in those receiving adoptive T-cell therapy.

A critical nuance in the data emerged when the researchers adjusted their models for the combined creatinine-cystatin C equation, known as eGFR cr-cys. The analysis showed that adjustment for the combined eGFR cr-cys equation attenuated the associations between discordance and the primary outcome of kidney injury or death in both patient cohorts. This attenuation, or weakening of the statistical link, suggests that while the 30% gap itself is a potent red flag for the clinician, the combined equation may integrate the physiological information provided by both biomarkers more effectively than looking at the discrepancy in isolation. For the practicing physician, these results emphasize that when a discrepancy is suspected, the combined equation provides a more refined assessment of a patient's true renal reserve and overall prognosis before beginning conditioning or lymphodepleting chemotherapy.

Hematologic Recovery and Clinical Implications

The clinical impact of a 30% or greater gap between creatinine and cystatin C filtration estimates extends beyond immediate renal failure and mortality to encompass broader measures of marrow function and systemic recovery. In this multicenter study, the researchers evaluated several secondary outcomes to determine if this renal discordance could serve as a proxy for physiological frailty. These secondary outcomes included time-to-platelet engraftment in hematopoietic stem cell transplant recipients and the presence of prolonged cytopenia, defined as a sustained and clinically significant reduction in mature blood cell counts, among those receiving adoptive T-cell therapies. By tracking these metrics, the authors sought to understand how pre-treatment renal biomarkers might predict the bone marrow's ability to recover following intensive conditioning or lymphodepleting chemotherapy.

The data revealed a consistent link between renal discordance and delayed hematologic reconstitution across both treatment modalities. Specifically, the researchers found that eGFR discordance was associated with a slower time-to-platelet engraftment in hematopoietic stem cell transplant recipients, suggesting that patients with over-estimated renal function may face a more protracted period of transfusion dependence and bleeding risk. A similar pattern emerged in the cellular therapy cohort, where eGFR discordance was associated with prolonged cytopenia following adoptive T-cell therapy. These findings indicate that the discrepancy between creatinine and cystatin C is not merely a narrow indicator of kidney health, but a meaningful marker of a patient's overall biological reserve. For the practicing clinician, identifying this discordance prior to therapy provides a more nuanced risk profile, highlighting patients who may require more intensive supportive care and closer monitoring for hematologic complications during the post-infusion period.

References

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