Estimation of renal function by three CKD-EPI equations in Chinese HIV/AIDS patients

Abstract Assessing renal function accurately is important for human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS) patients. Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) recommended three equations to calculate estimated glomerular filtration rate (eGFR). There is evidence that eGFR based on the combination of serum creatinine and cystatin C is the most accurate of the three equations. But there is limited data on the comparison of three CKD-EPI equations in Chinese HIV/AIDS patients. The aim of our study was to compare the three CKD-EPI equations in Chinese HIV/AIDS population and assess renal function. Cross-sectional, single center, prospective study. One hundred seventy two Chinese adult HIV/AIDS patients were enrolled, including 145 (84.3%) males and 27 (15.7%) females. Mean age was 40(±12) years old. Overall mean eGFR based on serum creatinine, cystatin C and the combination of the 2 markers was 112.6(±19.0) mL/min/1.73 m2, 92.0(±24.2)mL/min/1.73 m2, and 101.7(±21.8)mL/min/1.73 m2, respectively (P = .000). The eGFR calculated by serum creatinine alone is higher than eGFR calculated by combination of serum creatinine and cystatin C, and eGFR calculated by cystatin C individual is lower than eGFR calculated by combination of the 2 markers. Of the 3 CKD-EPI equations, the CKD-EPIscr-cys equation may have the most accuracy in evaluating renal function in Chinese HIV/AIDS patients while the CKD-EPIscr equation may overestimate renal function and the CKD-EPIcys equation may underestimate renal function.


Introduction
Renal dysfunction is common in human immunodeficiency virus (HIV)/acquired immune deficiency syndrome (AIDS) patients and a risk factor for poor prognosis of these patients. [1][2][3][4] Assessing renal function accurately in the HIV/ AIDS patients is essential, because we need to adjust the drug dosage according to kidney function. Gold standard of measuring glomerular filtration rate (GFR) is testing the clearance of inulin, iohexol, or 99 Tc m -diathylenetriamine pentaacetic acid, but it , s so cumbersome that we rarely use it in clinical settings. [5] Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) recommended 3 equations to calculate estimated glomerular filtration rate (eGFR) for clinical applications in 2012 [6] : eGFR scr , eGFR cys, and eGFR scr-cys based on serum creatinine, cystatin C and the combination of the 2 markers respectively.
Prior studies indicated that, the sensitivity of eGFR equations based on serum creatinine is poor in HIV/AIDS patients, because serum creatinine values in these patients are significantly lower than general population. [7,8] In addition, a clinical study in USA demonstrated HIV-RNA > 400 copies/mL or lower CD4+ T cell count can lead to larger bias of eGFR based on cystatin C. [9] A meta-analysis revealed that serum cystatin C is a better biomarker for the diagnosis of CKD in the West than in Asia. [10] Inker LA found eGFR based on the combination of serum creatinine and cystatin C was more accurate than eGFR based on Editor: Franco Musio. This study was supported by (1) Study on non-AIDS related disease control strategies in patients with long-term antiviral therapy, The program for the 13th Five-year Plan of China(2017ZX10202101004); (2) Study for blood concentration of Efavirenz influenced by Rifampin in HIV/TB co-infected patients, Project for Capital Characteristics (Z171100001017053); (3) Exploration for the etiology of HIV-related kidney diseases, Young talents development fund "Budding" support program project, Beijing Ditan Hospital, Capital Medical University (DTMY201808).
The authors have no conflicts of interests to disclose.
The data used to support the findings of current study are available from the corresponding author on reasonable request. serum creatinine or cystatin C individually in HIV-positive population. [11] Until now, there is limited data on the comparison of 3 CKD-EPI equations in Chinese HIV/AIDS patients. The aim of our study was to contrast the 3 CKD-EPI equations in Chinese HIV/ AIDS population in a single center and evaluating renal function in these patients.

Study population
This was a cross-sectional prospective study on HIV/AIDS patients. A total of 190 Chinese HIV/AIDS patients admitted to Beijing Ditan Hospital from February to May 2019 were observed. Exclusion criteria were 1. younger than 18 years old; 2. the patients who had missing data.
Clinical information was collected from electronic medical records. The Ethics Committee of Beijing Ditan Hospital, Capital Medical University approved the study protocol. The approval numbers is Jdlkz 2019-056-02. We obtained written informed consent from each subject.

Laboratory measurements and eGFR equations
Serum creatinine was measured at Department of Clinical Laboratory in Beijing Ditan Hospital affiliated to Capital Medical University using enzymatic assay. Collected 3.5 ml fasting venous blood of eligible subjects, took serum after centrifugation for 15 min under 3000 r /min, conserved the serum in À80°C. Finally, remelted the frozen serum together for testing cystatin C. The cystatin C test reagent kit was produced by Zhangjiagang DIALAB Biotechnology Co. Ltd, China. Serum cystatin C was measured with automatic biochemical analyzer HITACHI 7600 using a latex enhanced immunoturbidimetric assay. The eGFR was calculated by 3 CKD-EPI equations [6] ( Table 1).

Statistical analysis
Data were analyzed using SPSS20.0 (SPSS Institute, Chicago IL, USA). Homogeneity of quantitative data were tested by Kolmogorov-Smirnov one-sample test. Data with normal distribution was presented as mean ±SD. If data was in abnormal distribution, it was presented as median (interquartile range). Categorical variables were prescribed as frequency and percentage. Comparisons between eGFR values calculated by 3 CKD-EPI equations (eGFR scr , eGFR cys, and eGFR scr-cys ) were carried out by using the Wilcoxon signed rank test. P values <.05 were considered statistically significant in this study.

Results
One of the 190 Chinese HIV/AIDS patients admitted to Beijing Ditan Hospital from February to May 2019 was ineligible because he was younger than 18 years old, and 17 of them were excluded because of missing values for serum cystatin C. Finally, 172 Chinese adult HIV/AIDS patients were enrolled, including 145 (84.3%) males and 27 (15.7%) females.

Subjects
Gender
The frequencies of patients in each eGFR category are described in Table 4. If we use different equations to calculate eGFR, we can see that the frequencies and percentages of patients in each eGFR category is different. Generally, we can see that, eGFR calculated by serum creatinine is higher than eGFR calculated by combination of the 2 markers, and eGFR calculated by serum cystatin C is lower than eGFR calculated by combination of the 2 markers. Table 5 provided more details about the comparison of eGFR classifications between CKD-EPI scr-cys equation and the other 2 equations. Of the 154 patients with eGFR scr ≥90 mL/min/1.73 m 2 , 23 patients presented eGFR scr-cys < 90 mL/min/1.73 m 2 , and 1 among them even showed eGFR scr-cys < 60 mL/min/1.73 m 2 . In the 14 patients who had eGFR scr located in 60-89 mL/min/1.73 m 2 , 4 of them presented eGFR scr-cys located in 30-59 mL/min/1.73 m 2 . Of the 131 patients with eGFR scr-cys ≥90 mL/min/1.73 m 2 , 30 patients had eGFR cys < 90 mL/min/1.73 m 2 . Of the 53 patients with eGFR cys located in 60-89 mL/min/1.73 m 2 , 30 patients had eGFR scr-cys ≥90 mL/min/1.73 m 2 .

Discussion
We used enzymatic method for the determination of serum creatinine, because previous studys indicated the enzymatic method is more accurate than Jaffe method. [12,13] In our study, the eGFR calculated by serum creatinine alone was 112.6(±19.0) mL/min/1.73 m 2 , which was the highest in the 3 CKD-EPI equations. And our data are consistent with prior studies. [8,14] Clara et al revealed serum creatinine may overestimate renal function in HIV-infected subjects. [8] In a cohort of HIV-infected women, Driver et al [14] found that the prevalence of CKD was higher with eGFR cys compared to eGFR scr . The overestimation of renal function and thus underestimating kidney impairment by serum creatinine in HIV/AIDS patients is due to decreasing serum creatinine concentrations in this population. Low muscle mass is common in HIV/AIDS patients. [15] Both HIV itself and HIV antiretroviral medications could lead to muscle disease and decrease the concentration of creatinine. [8,[16][17][18] It should be noted that, although dolutegravir or rilpivirine may inhibit renal creatinine secretion, leading to an increase in Table 2 Main demographic characteristics of 172 HIV/AIDS patients included in the study. Others indicate regimen which included 1-3 drugs of Abacavir, Lamivudine, Zidovudine, Stavudine, Tenofovir disoproxil fumarate, Emtricitabine, Nevirapine, Efavirenz, Dolutegravir, Raltegravir, and ritonavir-boosted lopinavir, meanwhile patients on each regimen 3. ART = antiretroviral therapy, 3TC = Lamivudine, DTG = dolutegravir, EFV = efavirenz, EVG/C/TAF/ FTC = Elvitegravir, Cobicistat, Emtricitabine and Tenofovir Alafenamide Fumarate Tablet, HIV = human immunodeficiency virus, LPV/r = ritonavir-boosted lopinavir, TDF = tenofovir disoproxil fumarate. Table 3 Differences of mean eGFR calculated by 3 CKD-EPI equations.
Comparation of variables Difference of mean (mL/min/1.73 m 2 ) P value * eGFR scr -eGFR cys 20.6 .000 eGFR scr -eGFR scr-cys 10.9 .000 eGFR cys -eGFR scr-cys À9.7 .000 See  0 (0%) 0 (0%) 0 (0%) eGFR = estimated glomerular filtration rate, CKD-EPI = Chronic Kidney Disease Epidemiology Collaboration, Cys = cystatin C, Scr = serum creatinine. Table 5 Comparison of eGFR classifications between CKD-EPI scr-cys equation and the other 2 equations.  serum creatinine in HIV/AIDS patients treated with these drugs, [19,20] this phenomenon was not been observed in our study. Maybe it's because there are few patients taking these drugs in our study (8 patients used dolutegravir and none took rilpivirine). Cystatin C is produced by all nucleated cells at a constant rate in the body and is less affected by muscle mass than creatinine. [21] An analysis on 922 HIV-infected subjects conducted by Choi A and colleagues revealed that eGFR based on cystatin C was significantly associated with 5-year all-cause mortality, whereas eGFR based on serum creatinine did not appear to be associated with mortality substantially. [22] Nevertheless, Bhasin et al found [9] eGFR based on cystatin C was significantly more biased than eGFR based on combination of serum creatinine and cystatin C in the HIV-positive group, and eGFR based on cystatin C was lower than measured GFR using plasma iohexol clearance. In our present study, we found the eGFR calculated by serum cystatin C is lower than eGFR calculated by combination of serum creatinine and cystatin C [92.0(±24.2) mL/min/1.73 m 2 vs 101.7(±21.8) mL/min/1.73 m 2 ]. So our result is in accordance with Bhasin et al despite we did not measure GFR with gold standard method. That is to say, eGFR based on combination of serum creatinine and cystatin C has greater GFR fidelity while eGFR based on cystatin C is a better predictor of clinical outcomes. This is not a contradiction. eGFR based on cystatin C had strong correlations with HIV-RNA viral load, CD4+ T cell count, hs-CRP, IL-6, and D-dimer in HIV-infected persons. [21] Emerging data from HIV-infected populations exhibited the strong associations between clinical events including all-cause mortality and inflammatory markers, notably IL-6 and Ddimer. [23][24][25] Consequently, inflammation may mediate the association between eGFR based on cystatin C and clinical events.
Similar outcomes were discovered in general populations. [26][27][28][29] Inker LA [26] found that the eGFR equation based on combination of serum creatinine and cystatin C was significantly more accurate than the eGFR equation based on cystatin C alone. A research performed by Chi [27] et al showed that the CKD-EPI scr-cys equation was more suitable for estimating renal function than the other equations in a Chinese general population. Zhu Y [29] also corroborated that CKD-EPI scr-cys formula had better diagnostic value, especially in young participants.
Our study has following advantages. Firstly, this is the first clinical study to compare 3 CKD-EPI equations conducted in Chinese HIV/AIDS population. Secondly, we used standardized serum creatinine and cystatin C measurements.
Our study also has limitations. Firstly, we did not directly measure GFR using gold standard method. Secondly, the number of patients was relatively small. Thirdly, there was no HIV/AIDS patients with eGFR < 15 mL/min/1.73 m 2 . A prospective larger scale study comparing the performance of different eGFR formulas with gold standard of measuring GFR in Chinese HIV/AIDS patients should be conducted in the future.

Conclusion
In conclusion, of the 3 CKD-EPI equations, the CKD-EPI scr-cys equation may have the most accuracy in evaluating renal function in Chinese adult HIV/AIDS patients as the CKD-EPI scr equation may overestimate renal function and the CKD-EPIcys equation may underestimate renal function.