A simplified creatinine index (SCI) is a reliable and inexpensive marker of muscle mass that can predict survival in patients on hemodialysis (HD), according to a new large observational study.
“SCI may fluctuate over time but remain in a quite acceptable variation in a clinical setting,” first author Bernard Canaud, MD, PhD, professor of nephrology at the School of Medicine at Montpellier University, Montpellier, France, told Renal & Urology News. It is a simple, bedside, cost-effective parameter for muscle assessment — a complement to nutritional assessment — with a high predictive value not only for death risk, but for falls and fracture risk as well, particularly among the elderly, he said. SCI decline also is a strong indicator of hospitalization risk. “Monitoring SCI may be used as physical activity indicator to guide and coach dialysis patients in order to trigger physical activity,” he said.
SCI reflects the creatinine generation rate of an individual HD patient and can account for such factors as dietary intake of meat. The SCI in mg/kg/d is a surrogate of active muscle mass, meaning that it may diverge from instrumental assessment of muscle, such as with DEXA, because these tools estimate all physical components of muscle (collagen and fat tissue), Dr Canaud explained.
The study included 23,495 incident and prevalent HD patients documented in the MONitoring Dialysis Outcome (MONDO) Initiative, an international retrospective study cohort comprising chronic HD patients from 41 countries. Of these, 2194 (9.4%) died during follow-up. The mean age of the patients was 61 years, and 56.8% were male. The average dialysis vintage was 4.46 years.
A total of 2194 patients (9.4%) died during follow-up. Each 1 mg/kg/d increase in SCI score was significantly associated with a 10% decreased risk of all-cause mortality in adjusted analyses, the investigators reported in Nephrology Dialysis Transplantation. In addition, the study found that declines in SCI score accelerated approximately 5 to 7 months prior to death.
The mean follow-up period was 265 days for patients who died and 337 days for those who survived. The patients who died tended to have lower SCI scores and a lower lean tissue index (LTI). They also had a lower post-HD weight and serum creatinine, albumin, and phosphate levels, as well as higher C-reactive protein levels and neutrophil:lymphocyte ratio.
Lenar Tatios Yessayan, MD, an associate professor in the department of nephrology at the University of Michigan in Ann Arbor, said the new study adds to the body of literature suggesting the SCI is valuable in assessing mortality outcomes. “I was not surprised by the results,” Dr Yessayan said. “Well-preserved amount of muscle mass is known to be one of the strongest nutritional indicators for survival among ESRD population. The patients in the study were mostly European Caucasian, possibly limiting the generalizability of the SCI to a more diverse population such as [in] the US.”
Mark E. Williams, MD, director of dialysis operations at Beth Israel Deaconess Medical Center and senior staff physician at the Joslin Diabetes Center, both in Boston, Massachusetts, said the SCI needs further investigation because the authors suggest that when albumin levels fall because of protein malnutrition, a decrease in SCI would have the advantage of being an earlier marker. “However, when secondary to inflammation, serum albumin levels are known to fall soon, within days to weeks,” Dr Williams said. “No data are present to determine how SCI levels behave in the same setting. There is ongoing review of the role of creatinine and creatinine reporting in diverse racial and ethnic groups, whereas the current report is limited to a somewhat homogeneous population.”
The new study was not designed to address whether the SCI could improve outcomes, but the SCI theoretically could trigger interventions, such as exercise or nutritional supplementation, which may be helpful in improving outcomes, he said.
Orlando M. Gutiérrez, MD, professor of nephrology and associate director of the division of nephrology at the University of Alabama in Birmingham, said the study helps confirm that surrogate measures of muscle mass and nutrition are important markers of overall health in patients on maintenance HD. “This is clinically relevant as muscle wasting and malnutrition are common problems in this population,” Dr Gutierrez said. “I think the results would be broadly applicable to a US or North American population. That being said, it is not clear to me that adding this index to other standard measures of nutrition in clinical practice would meaningfully improve morbidity or mortality.”
He added, “What we need to know in clinical practice is what information this index is adding above and beyond the standard measures collected as part of clinical care or whether it is basically providing the same information. If the latter is the case, then this index would likely not contribute much to improving morbidity or mortality,” he said.
Canaud B, Ye X, Usvyat L, Kooman J, et al. Clinical and predictive value of simplified creatinine index used as muscle mass surrogate in end-stage kidney disease haemodialysis patients—results from the international MONitoring Dialysis Outcome initiative. Published online August 24, 2020. Nephrol Dial Transplant. doi:10.1093/ndt/gfaa098
von Gersdorff GD, Usvyat L, Marcelli D et al. Monitoring dialysis outcomes across the world – the MONDO Global Database Consortium. Blood Purif. 2013; 36:165-172. doi:10.1159/000356088