#1483 Creatinine excretion can serve more than a marker of kidney function in patients in the late postoperative period of bariatric surgery
Authors: Almeida Jane , Lamarca Fernando Pardo , De Carvalho Kenia Mara Baiocchi 
Published: May 2024

Abstract

Background and Aims
Bariatric and metabolic surgery is the treatment of choice for severe obesity aiming to improve quality of life and control comorbidities, including chronic kidney disease (CKD). Careful monitoring of metabolic components, including markers of kidney function, are needed in the late postoperative period. The 24-hour urinary creatinine excretion rate (CER) and the Creatinine-Height Index (CHI) are accepted as non-invasive methods to evaluate kidney function, which are associated with skeletal muscle mass. However, it is not known whether these markers are also associated with muscle function among patients who underwent bariatric surgery after a period of massive weight loss. Therefore, the present study aims to investigate the association between kidney function markers with muscle function in individuals in the late postoperative period of bariatric surgery .

Method
This is a cross-sectional study, including women who underwent bariatric surgery for more than 18 months, when weight loss trajectory tends to stabilize. Age, date of surgery, self-reported preoperative weight, current body mass index (BMI) were collected to determine nutritional status. Patients with a BMI above 25 kg/m² were considered to have excessive body weight. Total weight loss (%TWL) and excess weight loss (%EWL) after surgery were also calculated. Patients underwent a blood test to assess serum creatinine (mg/dL) and collected 24-hour urine to estimate CER and CHI. Urinary collection was checked for adequate collection and patients with inadequate collections were excluded from the analysis. Muscle function comprised the assessment of muscle strength by handgrip strength [(HGS) JAMAR®, USA], 30-second chair stand test (30-CST) and, physical performance by timed-up and go test (TUG). Pearson's correlation was performed to test the correlation between the variables of interest and independent T-test to compare differences in creatinine markers and muscle function in the groups of patients with normal and excessive body weight.

Results
We analyzed 89 women (mean age 39.4 ± 8.0 years; BMI 28.6 ± 4.7 kg/m²). Bariatric surgery were at a median time of 3.9 (1.7 – 6.6) years post-operative; %TWL and %EWL were 38.0 ± 8.5% and 79.1 ± 20.2 %, respectively. Mean serum creatinine, CER and CHI were 0.67 ± 0.12 mg/dL; 5.7 ± 2.7 mmol/L; and 120.1 ± 22.5%, respectively. Significantly higher muscle strength was found between patients with excessive body weight (n = 69) compared to those with normal body weight (n = 20) for the HGS (29.2 ± 5.1 vs. 26.5 ± 5.8 kgf, p = 0.037) but not for the 30-CST (15.3 ± 4.0 vs. 14.4 ± 3.7 repetitions, p = 0.181) or performance by TUG test (6.1 ± 0.90 vs 6.1 ± 0.95 seconds, p = 0.450). Considering the total sample, HGS was significantly correlated with CHI (r2 0.238, p = 0.025, ) but not with serum creatinine or CER (r2 0.180, p = 0.093; r2 -0.047, p = 0.662, respectively). No significant correlations were found between the creatinine variables with 30-CST and TUG tests, except among patients with excessive body weight, where CER showed a significant correlation with the 30-CST test (r2 0.257, p = 0.034).

Conclusion
In addition to the already known effects on muscle mass, creatinine variables were correlated with muscle strength and, among those who still present excessive body weight after bariatric surgery, also with muscle functionality. Further studies may clarify mechanisms involved in physical function and creatinine excretion after a massive weight loss promoted by bariatric surgery. Determination of creatinine excretion could be useful in addition to the imaging technique arsenal available for metabolic assessment in studies with this population set.