体重指数对胱抑素C公式法估算肾小球滤过率的影响

Effect of Body Mass Index on Evaluation of Glomerular Filtration Rate Using Equations Based on Cystatin C

摘要: 目的：探讨体重指数(BMI)对基于胱抑素C (CysC)公式法评估肾小球滤过率(eGFR)的影响。方法：收集我院体检科2018年1月至2018年12月体检的、资料完整的健康人群308例。BMI计算按公式BMI (kg/m²) = 体重(kg)/[身高(m)]²，BMI ≥ 28 kg/m²定义为肥胖，BMI 24.0~27.9 kg/m²定义为超重，BMI 18.5~23.9 kg/m²定义为正常。年龄 > 40岁定义为中老年人，年龄 ≤ 40岁定义为青年人。CKD定义及分期按KDOQI标准。采用胶体颗粒增强免疫比浊法检测血清CysC，>1.55 mg/L定义为CysC升高；采用苦味酸法检测血肌酐(Scr)，血肌酐升高定义为：男 > 97 umol/L，女 > 81 umol/L。用慢性肾脏病流行病学合作研究公式(CKD-EPI_Scr-Scys, CKD-EPI_Scr, CKD-EP_Scys)、CG公式、中国改良MDRD公式估算GFR (eGFR)。用SPSS22.0统计软件进行统计学分析，以p < 0.05为差异有统计学意义。结果：1) 308例健康体检者中，女性48例(15.6%)。平均年龄37岁 ± 9.7岁(20岁~81岁)。平均BMI 24.6 ± 1.5 (21.0~30.1) kg/m²，其中肥胖6例，超重200例，BMI正常102例。平均Scr为72.5 ± 11.3 (41~102) umol/L，其中血肌酐升高6例。平均CysC 0.81 ± 0.13 (0.57~1.61) mg/L，其中CysC升高2例。5种公式估算的平均eGFR分别为：eGFR (CKD-EPI_Scr-Scys) 119.9 ± 13.5 ml/min/1.73m²，诊断CKD 2例(0.65%)；eGFR (CKD-EPI_Scr) 110.3 ± 11.9 ml/min/1.73m²，诊断CKD 2例(0.65%)；eGFR (CKD-EPI_Scys) 105.3 ± 20.5 ml/min/1.73m²，诊断CKD 12例(3.90%)；eGFR (CG公式) 120.7 ± 20.1 ml/min/1.73m²，诊断CKD 2例(0.65%)；eGFR (改良MDRD) 116.7 ± 20.1 ml/min/1.73m²，诊断CKD 0例(0%)。2) 与青年人比较，中老年人CysC水平明显升高(p = 0.000)，CKD-EPI_Scr-Scys、CKD-EPI_Scr、CKD-EPI_Scys、CG公式、改良MDRD五种公式估算的GFR值均明显降低(p均为0.000)。3) 由于研究人群肥胖人数少，我们按三分位法把BMI分为三组：BMI < 24.0 kg/m²组、BMI 24.0~25.3 kg/m²组、BMI > 25.3 kg/m²组。结果显示，CysC水平及eGFR (CKD-EPI_Scr-Scys)、eGFR (CKD-EPI_Scys)在三组之间无显著差异(p分别为1.000，0.343，0.859)。但Scr水平及eGFR (CKD-EPI_Scr)、eGFR (改良MDRD)在三个BMI分组之间有显著差异(p分别为0.002，0.005，0.001)，eGFR (CG公式)总体差异不显著(p = 0.07)。结论：健康体检人群血清CysC水平和基于CysC公式(CKD-EPI_Scr-Scys, CKD-EP_Scys)估算eGFR不受BMI影响。这可能与本研究肥胖例数少有关。CysC与肥胖之间关系的研究需要进一步改进肥胖的诊断标准比如采用体脂而不是BMI。

Abstract: Objective: To investigate the effect of body mass index (BMI) on the evaluation of glomerular filtration rate (eGFR) using equations based on the cystatin C (CysC). Methods: A total of 308 healthy people with complete medical records from January to December 2018 in our department of physical examination were collected. BMI calculation formula is BMI (kg/m²) = body weight (kg)/[height (m)]2, and BMI ≥ 28 kg/m² is defined as obesity, BMI 24.0 - 27.9 kg/m² as overweight, and BMI 18.5 - 23.9 kg/m² as normal. Age > 40 years old is defined as middle-aged and elderly, and age ≤ 40 years old is defined as young people. The CKD definition and staging are based on the KDOQI standard. Serum CysC was detected by colloidal partical enhanced immunoturbidimetry; >1.55 mg/L was defined as elevated CysC; serum creatinine (Scr) was detected by picric acid method, and elevated creatinine was defined as: male >97 umol/L, female > 81 umol/L. GFR (eGFR) was estimated using the Chronic Kidney Disease and Epidemiology (CKD-EPI) equation using creatinine (CKD-EPI_Scr), cystatin (CKD-EPI_Scys) and the combination of cystatin and creatinine (CKD-EPI_Scr-Scys), CG equation, and China’s modified MDRD equation. Statistical analysis was performed using SPSS 22.0 statistical software, and the difference was statistically significant at p < 0.05. Results: 1) Of the 308 healthy subjects, 48 (15.6%) were women. The average age is 37 ± 9.7 years old (20 ± 81). The average BMI was 24.6 ± 1.5 kg/m² (21.0 - 30.1), including 6 cases of obesity, 200 cases of overweight and 102 cases normal. The average Scr was 72.5 ± 11.3 umol/L (41 - 102), and serum creatinine was increased in 6 cases. The average CysC was 0.81 ± 0.13 mg/L (0.57 - 1.61), and CysC was increased in 2 cases. The average eGFR is estimated by the five equations respectively: eGFR (CKD-EPI_Scr-Scys) 119.9 ± 13.5 ml/min/1.73m², 2 cases with diagnosed CKD (0.65%); eGFR (CKD-EPI_Scr) 110.3±11.9 ml/min/1.73m², 2 cases with diagnosed CKD (0.65%); eGFR (CKD-EPI_Scys) 105.3 ± 20.5 ml/min/1.73m², 12 cases with diagnosed CKD (3.90%); eGFR (CG) 120.7 ± 20.1 ml/min/1.73m², 2 cases with diagnosed CKD (0.65%); eGFR (modified MDRD) 116.7 ± 20.1 ml/min/1.73m², 0 case with diagnosed CKD (0%). 2) Compared with young people, the CysC level of middle-aged and elderly people was significantly increased (p = 0.000), and the GFR was significantly decreased (p = 0.000) estimated by the five equations of CKD-EPI_Scr-Scys, CKD-EPI_Scr, CKD-EPI_Scys, CG and modified MDRD. 3) Because of the small number of obese people in the study population, we divided them into three groups based on BMI tertiles: BMI < 24.0 kg/m² group, BMI 24.0 - 25.3 kg/m² group, and BMI > 25.3kg/m² group. The results showed that CysC levels and eGFR estimated by CKD-EPI_Scr-Scys and CKD-EPI_Scys were not significantly different among the three groups (p = 1.000, 0.343, 0.859, respectively). However, among the three groups, there were significant differences in Scr levels and eGFR estimated by CKD-EPI_Scr and modified MDRD (p = 0.002, 0.005, 0.001, respectively), but no difference in eGFR estimated by CG (p = 0.07). Conclusions: In healthy subjects, serum CysC levels and eGFR estimated by the CysC-based equations (CKD-EPI_Scr-Scys, CKD-EP_Scys) are not affected by BMI. This may be related to the small number of obese cases in this study. The study of the relationship between CysC and obesity requires further improvement in the diagnostic criteria for obesity such as the use of body fat rather than BMI.