Evaluating kidney health often involves looking at a measure known as the glomerular filtration rate (GFR), which essentially tells us how well the kidneys are working. However, achieving an accurate measurement of GFR is not easy. Almost all of the the creatinine, a key substance used to estimate GFR, is derived from our muscles. The influence of muscle mass on serum creatinine  complicates the assessment of kidney health. As we age, there is a decline in muscle strength and bulk, a condition known as sarcopenia. Starting around 30, this loss speeds up significantly after 60, potentially cutting muscle mass in half by 80. Since creatinine levels depend on muscle mass, changes in muscle due to age, sex, and fitness level can lead to inconsistencies in kidney health evaluations.

A recent study, led by Professor Jeong-Ho Kim from Yonsei University College of Medicine, and conducted with Professor Jisook Yim from Korea University College of Medicine, Professor Nak-Hoon Son from Keimyung University, along with Professor Taeyoung Kyong and Professor Yongjung Park, also from Yonsei University College of Medicine, has explored this complex relationship, focusing on older adults.Their research, published in the journal Heliyon, investigates how age and gender play a role in the link between muscle mass and serum creatinine levels in a healthy elderly population.

The study examined data from a substantial number of participants from the Korea National Health and Nutrition Examination Survey (KNHANES) and the Health Check (HC) groups. The team measured serum creatinine levels and skeletal muscle mass index (SMI), a gauge of muscle bulk, using bioelectrical impedance analysis techniques. They found that in older men, muscle bulk decreases more noticeably with age compared to women. This decline in muscle bulk in men also corresponds with a more marked decrease in serum creatinine levels, both in the KNHANES and HC groups. In contrast, the relationship between creatinine levels and age was not as pronounced in women in either group.

Professor Jeong-Ho Kim, pointed out an important discovery from their work, stating, “Creatinine seum levels decrease more significantly in older men than in older women due to the more noticeable reduction in muscle mass in men.” This finding highlights the importance of considering gender differences when evaluating kidney health in older adults, advocating for a gender-specific approach in these assessments.

The team also created a model to predict creatinine levels, considering factors like muscle bulk, age, and gender. This model indicates that a significant part of the variability in creatinine levels in both the KNHANES and HC groups can be explained by these factors. The formulas developed in the study help in understanding the interplay of muscle mass, age, and gender in influencing creatinine levels.

In his closing remarks, Professor Kim emphasized the wider implications of their research: “Differences in muscle mass reduction between older men and women are crucial to consider for accurate GFR calculations. The noticeable decrease in muscle bulk in older men, contrasted with the more stable or even increasing muscle mass in older women, calls for a reexamination of age-related factors in GFR calculations for different genders, particularly those over 65.” He underscored the need for ongoing research to ensure precise GFR calculation in older populations, taking into account the growing number of elderly people and the age range of patients in healthcare settings.

In summary, this study sheds light on the significant role of muscle mass in serum creatinine levels, particularly in older adults, and underscores the vital differences between genders in this aspect. It advocates for a gender-specific approach in estimating kidney health in the elderly. This research not only deepens our understanding of kidney health evaluation but also leads the way for more individualized and precise healthcare for older adults.

Journal Reference

Jisook Yim, Nak-Hoon Son, Taeyoung Kyong, Yongjung Park, Jeong-Ho Kim, “Muscle mass has a greater impact on serum creatinine levels in older males than in females”, Heliyon, 9 (11) (2023). DOI: https://doi.org/10.1016/j.heliyon.2023.e21866 .

About the Authors

Jisook YIM, M.D.,Ph.D

Dr Jisook YIM, a clinical assistant professor at Korea University Anam Hospital, College of Medicine, Korea University, specializes in clinical chemistry and genetics. With a Ph.D., from Yonsei University College of Medicine, her research spans kidney disorders, geriatrics, newborn screening, metabolic and endocrine disorders, and biomarkers. Formerly at Catholic Genetic Testing Center at Seoul St. Mary’s Hospital, College of Medicine, Catholic University of Korea, her interests have since expanded to clinical genetics and molecular genetics, where she explores testing, diagnosis, and genetic counseling for congenitaldisorders. Additionally, her current research portfolio includes cancer genetics for precision medicine.

Jeong-Ho KIM, M.D.,Ph.D

Dr. Jeong-Ho KIM is a professor in the Department of Laboratory Medicine at Yongin Severance Hospital, Yonsei University College of Medicine (YUCM), Republic of Korea. He earned his MD degree in 1983 and later achieved his PhD degree in 1995, both from YUCM. He completed his residency in clinical pathology at Severance Hospital in 1987. He has served as the director of the Department of Laboratory Medicine at three affiliated hospitals with YUCM, including Gangnam Severance, Severance, and Yongin Severance. His primary research interests are the standardization of lipids, preanalytical factors, and therapeutic drug monitoring. His current research particularly focuses on the metabolomic studies through proteomic analysis using mass spectrometry for the early diagnosis or therapeutic monitoring of various diseasess, such as chronic kidney disease, cardiovascular diseases, bowel diseases, and many types of cancer.