CKD is defined as reduced kidney function or kidney damage from a variety of causes. CKD is divided into five stages based on glomerular filtration rate[10-11]. Renal function can also be measured by serum creatinine (SCR) or endogenous creatinine clearance . Currently, ultrasound examination technology has been widely used in the prediction and diagnosis of different diseases. Xu et al  used real-time tissue elastography to predict the occurrence of esophageal varices in patients with chronic hepatitis B associated cirrhosis. Simicic Majce et al  used contrast-enhanced ultrasound to assess the effect of renal reflux. De Freminville et al  predicted the mortality rate of renal transplant patients with renal resistance index (RI) measured by ultrasound technique. Different from the clinical application of creatinine or glomerular filtration rate in the diagnosis of CKD, this study used color Doppler quantitative region of interest (ROI) technique combined with assay indexes to predict the early onset of CKD and establish a Nomogram prediction model.
As previously reported , changes in renal blood perfusion are closely related to renal function. Unlike CTA (CT angiography) and radionuclide examination, color Doppler imaging provides a non-invasive, convenient, and non-radiological method for evaluating renal blood flow[17-18]. Color Doppler region of interest quantitative technology through the acquisition of original signals, combined with QLAB software quantitative analysis, calculate the renal blood perfusion index. VI represents the number of vascular beds in ROI; Fi: represents the average flow rate of blood flow in all vessels in ROI; VFI=VI×FI, then represents the blood perfusion of ROI[19-20]. At present, Liu  has applied the color Doppler region of interest quantitative technique to the prediction of intraoperative bleeding of scar uterine, and the results suggest that VI may be helpful in predicting intraoperative massive bleeding of scar uterine pregnancy. Mala et al  applies this technique to the diagnosis of polycystic ovary, and the results suggest that the adnadal VI and VFI of women with polycystic ovary are significantly increased, and the indicators measured by the quantitative region of interest (ROI) technique can be used as one of the diagnostic criteria for polycystic ovary. Therefore, this study is to investigate whether VI, FI and VFI could be used as diagnostic indicators of CKD.
In this study, it was found that the mean values of VI, FI and VFI in the CKD group were lower than those in the control group (P<0.05), and FI and VFI were independent risk factors for early chronic kidney disease. Consistent with the results of D 'Amico et al, the number of vascular beds in the CKD group was reduced, the velocity of intravascular blood flow was slowed, and the perfusion of renal tissue was also reduced. Possible reasons for this result are: (1) Extracellular matrix deposition occurs during the development of chronic renal disease, resulting in interstitial fibrosis and other pathological changes. Subsequently, circulatory resistance increases, renal hemodynamics changes, and perfusion volume decreases. (2) After renal function is impaired, the activation of various cytokines leads to the increase of renal artery resistance, the decrease of intravascular velocity and the decrease of blood perfusion. (3) Under the state of oxidative stress, various signaling pathways are activated, leading to the decrease of renal blood perfusion. The above reasons together present the outcome of "high resistance and low perfusion", leading to the decrease of FI and VFI.
Multivariate logistic regression analysis suggested that albumin, hypertension, diabetes and urea nitrogen were also independent risk factors for stage I-II CKD. Albumin, as an indicator of nutritional status, is often used in the diagnosis of various chronic diseases. In patients with CKD, proteinuria occurs due to decreased glomerular filtration and loss of protein. Decrease in serum albumin, coupled with malnutrition in chronically ill patients and inadequate supplementation, leads to further albumin decline. According to ROC results, the truncation value of albumin was 40.26g/L. When this value is exceeded, physicians should be on guard against the occurrence of chronic kidney disease in combination with the medical history. When patients develop hypertension, renal hemodynamics will change. Persistent hyperfiltration leads to impaired glomerular barrier function, which in turn leads to limited glomerular filtration. The organ most commonly affected by diabetes is the kidney. The damage of high glucose to the kidneys involves not only the glomeruli but also the tubules. Hypertension and diabetes mellitus are risk factors for CKD progression to end-stage renal disease [24-25]. Therefore, early and effective control of blood pressure and blood glucose can prevent the occurrence and deterioration of CKD to a certain extent. According to the histogram, it can be seen that BUN also has a good ability to identify CKD in the early stage. Urea nitrogen is filtered out of the glomerulus. When microcirculation is damaged and basement membrane is damaged, BUN will increase inversely proportional to the glomerular filtration rate . In summary, FI, VFI, BUN, albumin, hypertension and diabetes are independent risk factors for early CKD, and Nomogram can provide an effective risk assessment for CKD.
In comparison of baseline data, there was no statistically significant difference in RI between the CKD group and the control group. It may be because in the early stage of CKD, although the renal blood perfusion is reduced, the renal vasoconstriction is not obvious. In the early stage, the kidney is in the compensatory stage, and there are few structural changes, such as renal length and cortical thickness. This findings suggest that gender has no role in early CKD, but previous studies have found a 9 percent higher prevalence in women than in men . Gender and age did not become independent risk factors in this study. The possible reason is that the included samples are relatively limited and biased. The scope of the included population can be appropriately expanded, the sample size can be appropriately increased, and more patients from different regions can be included in the study. The weakness of this study is the lack of external verification for Nomogram, which requires a large amount of data to make prospective prediction.