Adding age to glomerular filtration rate calculation improves hyperfiltration detection
Key takeaways:
- Older adults may have hyperfiltration with normal glomerular filtration rate calculation.
- GFR calculation may be more accurate without correcting for body surface area.
An equation for detecting hyperfiltration that incorporates age but not body surface area may improve early identification of diabetic nephropathy, according to findings from researchers in Japan.
Hyperfiltration may not be detected for patients with obesity using the current method of determining glomerular filtration rate corrected for body surface area, Akihiro Tsuda, MD, PhD, a lecturer in the department of metabolism, endocrinology and molecular medicine at Osaka Metropolitan University Graduate School of Medicine in Japan, told Healio. Furthermore, GFR declines naturally for older adults, making identification of hyperfiltration difficult in that population as well.
“So, we defined hyperfiltration using GFR without body surface area correction and with correction for aging,” he said.
Tsuda and colleagues assessed data from 180 adults (mean age, 56.4 years; 79 men) collected during evaluation as potential kidney donors. Participants were categorized into four groups based on glucose tolerance and BMI: 74 participants had normal glucose tolerance without obesity; 14 had normal glucose tolerance with obesity; 63 had prediabetes or diabetes without obesity; and 29 had prediabetes or diabetes and obesity.
Serum albumin, eGFR assessed by creatinine and cystatin C, GFR assessed by inulin clearance with body surface area correction, and renal plasma flow were similar in all four groups. However, the group with prediabetes or diabetes plus obesity had significantly higher blood pressure, urinary albumin excretion (UAE) and levels of hemoglobin and uric acid than the other participants. GFR assessed by inulin clearance but without body surface area correction was significantly higher for that group as well, suggesting the GFR calculation incorporating body surface area and eGFR were unable to detect hyperfiltration, according to the researchers.
In addition, older age was significantly associated with lower renal plasma flow and GFR with or without correction for body surface area, suggesting that hyperfiltration may be present with normal GFR for older adults, according to the researchers.
The equation researchers determined for greater accuracy in assessing hyperfiltration is GFR = 0.883 x age + 167.398.
“It is difficult to measure inulin clearance due to the relative complexity of the method, and we cannot detect hyperfiltration precisely, in routine practice. However, evaluation of GFR using eGFR prevents judgment of whether high eGFR is caused by overestimation or hyperfiltration since eGFR is inaccurate in kidney donor candidates [with] diabetes. Thus, we cannot detect hyperfiltration by eGFR, but UAE may be valid for this purpose,” Tsuda said. “In fact, it is well known that the pathogenic significance of UAE is its link to glomerular hypertension and hyperfiltration, and in this study, the presence of hyperfiltration was associated with UAE. However, it is difficult to set a UAE cutoff to detect hyperfiltration, and a further cohort study is needed to determine this cutoff value.”
References:
Age matters: Kidney disorder indicator gains precision. Available at: https://www.omu.ac.jp/en/info/research-news/entry-69602.html. Published Jan. 6, 2025. Accessed Jan. 23, 2025.
Tsuda A, et al. Hypertens Res. 2024;doi10.1038/s41440-024-02020-y.
For more information:
Akihiro Tsuda, MD, PhD, can be reached at naranotsudadesu@omu.ac.jp.
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