Non-cystic fibrosis bronchiectasis is a common lung disease in which low body weight and BMI are in more common. The prevalence of malnutrition is higher in bronchiectasis compared to other lung diseases. A study on the assessment of nutritional status in end-stage lung disease noted a higher prevalence of malnutrition in patients with CF or NCFB according to the GLIM framework. Therefore nutritional status is a condition of concern in patients with non-cystic fibrosis bronchiectasis. The Bronchiectasis Severity Score (BSI), of which BMI is a component, is a useful prognostic measure, and it is reasonable to assume that BMI correlates with the severity of bronchiectasis.BMI is an easily accessible nutrition-related criterion, and many studies have been conducted on the correlation between BMI and prognosis, including hospitalisation, in patients with bronchiectasis. It has been shown that BMI is an independent predictor of hospitalisation and that patients with lower BMI are more likely to have acute exacerbations, worsening lung function, increased systemic inflammation and chronic colonisation by Pseudomonas aeruginosa. It has now been shown that reduced muscle mass in patients with lower nutritional status (especially fat-free mass index) is thought to contribute to worsening lung function in patients with COPD. This phenomenon may still be present in patients with bronchiectasis.BMI, a commonly used body measure in clinical practice, is easy to obtain but does not adequately reflect the nutritional status of the participants, so the researchers included new nutritional parameters such as upper arm circumference, calf circumference, grip strength, skinfold thickness, upper arm muscle circumference, and defatted body mass index in order to comprehensively assess the nutritional status of the patients, and to clarify the relationship between nutritional status and bronchiectasis. correlation between nutritional status and the presence of prognosis in bronchiectasis. According to the inclusion and exclusion criteria, participants with confirmed diagnosis of bronchiectasis attending the Union Hospital of Tongji Medical College of Huazhong University of Science and Technology from 31 March 2024 to 31 March 2027 will be included in this study. At the time of enrolment, the researchers collected the demographic information of the participants such as gender, age, measurement of their height (m), weight (kg), skinfold thickness (including triceps brachii, back, and abdomen) (mm), upper arm circumference (cm), calf circumference (cm), grip strength (average of two measurements in kilograms using a grip strength meter), and data from bioelectrical impedance analysis (phase angle (phA), total fat mass (FM), fat-free mass (FFM), skeletal muscle mass (SMM) ), and blood test results such as red blood cell count (10\^12/l), haemoglobin (g/l), triglycerides (mmol/l), LDL cholesterol (mmol/l), HDL cholesterol (mmol/l), and blood glucose (mmol/l) were collected from the participants' blood tests at the time of their visit. The results of pulmonary function tests, such as the patient's FEV1 and FEV1 as a percentage of the expected value, and imaging tests of the lungs, such as CT, were also used to calculate the patient's nutrition-related indices, such as BMI (kg/m\^2), fat-free mass index (FFMi), and the patient's nutrition-related indices, such as BMI (kg/m\^2) and FFMi (FFMi). free mass index (FFMi) and skeletal muscle mass index (SMMi)), and the participants' PNI index, CONUT index, HALP index, GNRI index, GPS index, and Bhalla Scoring. After enrolment, the participants were grouped into malnourished and non-malnourished groups according to the GLIM criteria based on the nutritional status of the patients. Over the next three years, the patients were followed up every six months to obtain the above nutritional indices, pulmonary function and lung CT results, as well as the number of acute exacerbations, the number of hospitalisations, and the survival status of the patients per year, in order to conclude the relationship between nutritional status and the progression of bronchiectasis.

Methods： Height, weight, upper arm circumference, calf circumference and waist circumference were determined while the patients were fasting and wearing only light clothing. Waist circumference was determined to the nearest 0.1 cm. Waist circumference was measured just above the ilium using flexible plastic measuring tape. Upper arm circumference is measured at the triceps belly. Calf circumference is measured at the quadriceps belly.Body height (in meters) was measured using a normal height scale and body weight was determined using digital devices . BMI was determined using the following formula: body weight in kilograms divided by body height in meters squared.

Handgrip strength was measured on three separate occasions . This was performed with the patient seated on a chair, with their shoulder and forearm in a neutral position and the elbow at 90 degrees of flexion. The participant performed a maximum grip force for 3 s and rested for 1 min between each repetition.

Total fat mass and total fat-free mass were determined via bioelectrical impedance (BIA) analysis with a total accuracy of 50 g. The bioelectrical impedance analysis was performed in a standardized manner, with the patient fasting for 8 h and resting for 30 min. The electrodes were placed distally on the wrists and ankles of the patients, with the patients in a supine position and having assumed a lying position 30 min beforehand. Absolute fat-free mass (FFM) and skeletal muscle mass (SMM) were determined directly via impedance. Then, FFMi (fat-free mass index) was determined by dividing absolute FFM by squared height (FFM (kg)/height (m2)); SMMi (skeletal muscle mass index) was also determined by dividing SMM by squared height. Subjects were separated into 2 groups according to their median SMMi values.

The CONUT score was calculated from the results of three laboratory tests, including serum albumin level, total lymphocyte count and cholesterol level. The calculation formula of the PNI score was as follows: 10∗serum albumin level (g/dL) + 0.005∗ total lymphocyte count (number/mm3). The GNRI score was calculated as 14.89 ∗ serum albumin level (g/dL) + 41.7 ∗ (current weight/ideal weight), and the ideal weight was calculated as 22 ∗ height squared. The HALP score is calculated as HALP Score = \[hemoglobin (g/L) \* albumin (g/L) \*lymphocytes (/L)\]/platelets (/L).The Glasgow prognostic score (GPS) is evaluated using serum CRP and albumin levels.Lung CT scores were scored according to the Bhalla scoring criteria and were co-scored by two medical imaging physicians.

Statistical analysis and statistical methods： The data obtained during the study were pre-collated. For continuous data, normality tests were first performed. If all groups met normality, the Student's t-test was used for comparison between groups. Otherwise, the non-parametric Wilcoxon rank sum test was considered. For categorical variables, the χ2 test was used. Statistically significant data were subjected to multivariate logistic regression analysis. Receiver operating characteristic (ROC) and Delong's method were used to analyze the effect of different nutritional status on the prognosis of participants with bronchiectasis，with a difference considered statistically significant at P \< 0.05.

Statistical analysis of all data was performed through SPSS (IBM SPSS Statistics 26.0, SPSS Inc., Chicago, IL) and R language (version 4.1.3, www.R-project.org/). All statistical tests were two-sided, and statistical significance was set at 0.05.