Liver Function Tests

This study included consecutive patients with biopsy-proven NAFLD who attended specialist fatty liver clinics at the Freeman Hospital, Newcastle upon Tyne, UK; Addenbrooke's Hospital, Cambridge, UK; Antwerp University Hospital, Edegem, Belgium; and Pitié-Salpêtrière Hospital, Paris, France. These formed the initial ascertainment cohort. Liver biopsies were conducted as per routine clinical care for the investigation of abnormal liver function tests (raised ALT, AST, or gamma-glutamyl transferase) or to stage disease severity in patients with radiological evidence of fatty liver. Clinical and laboratory data were collected prospectively from the time of liver biopsy. Patients with evidence of other liver disease (autoimmune hepatitis, viral hepatitis, drug induced liver injury, hemochromatosis, cholestatic liver disease, or Wilson's disease) were excluded. In addition, subjects consuming excessive amounts of alcohol (alcohol intake >20 g/day for women; >30 g/day for men) at the time of biopsy or in the past were excluded. Patients with incomplete data to calculate all the non-invasive scores were excluded.
Relevant clinical details, including gender, age, weight, and height, were obtained at the time of biopsy. The body mass index was calculated by the formula: weight (kg)/height (m)². Patients were identified as having diabetes if they had been diagnosed with diabetes according to the 2004 American Diabetes Association criteria or if they were taking an oral hypoglycemic drug or insulin (23 (link)).
Percutaneous liver biopsies were performed as per unit protocol at the sites and were assessed by an experienced local hepatopathologist. Patients with liver biopsies specimens <15 mm in length were excluded. Histological scoring was performed according to the non-alcoholic steatohepatitis (NASH) Clinical Research Network criteria (24 (link)). The NAFLD activity score was graded from 0 to 8, including scores for steatosis (0–3), lobular inflammation (0–3), and hepatocellular ballooning (0–2). NASH was defined as steatosis with hepatocyte ballooning and inflammation ± fibrosis (25 (link)). Fibrosis was staged from F0 to F4 (24 (link)). Patients with stage F3 or F4 fibrosis were considered to have advanced fibrosis.
The AST/ALT ratio, FIB-4, and NFS were calculated from blood tests taken at the time of liver biopsy as previously described (16 (link), 26 (link), 27 (link)). Details of the formulas and cutoffs for the tests under investigation are shown in Table 1. Previously published cutoffs were used to exclude and diagnose advanced fibrosis for each score (15 (link), 16 (link), 18 (link), 19 (link))
To validate new cutoffs for the NFS and FIB-4 score optimized for use in older patients (aged ≥65 years) that were derived in the initial ascertainment cohort, anonymized biochemical, histological, and anthropometric data were collected from a separate group of histologically characterized patients from the EPoS/EASL European NAFLD Registry. The “European NAFLD Registry” was established during the EU FP7 FLIP project (2010-) and is now maintained by the EU H2020 EPoS (Elucidating Pathways of Steatohepatitis) consortium to facilitate collaborative research into NAFLD. It is the largest multi-national registry of patients with histologically characterized NAFLD. These patients had data collected according to the same methodology as the main cohort.
All statistical analyses were performed using the SPSS software version 22.0 (SPSS, Chicago, IL). Continuous normally distributed variables were represented as mean ± s.d. Categorical and non-normal variables were summarized as median and range. Chi squared tests were used to determine the distribution of categorical variables between groups. To compare the means of normally distributed variables between groups, the Student's t-test or analysis of variance test was performed. To determine differences between groups for continuous non-normally distributed variables, medians were compared using the Mann–Whitney U-test. The diagnostic performance of the non-invasive tests was assessed by receiver operating characteristic (ROC) curve analysis. The area under the ROC (AUROC) was used as an index to compare the accuracy of tests. The sensitivity, specificity, positive predictive values (PPVs), negative predictive values (NPVs), positive likelihood ratios (LR +ve), and negative likelihood ratios (LR −ve) for relevant cutoffs were also displayed. In order to assess changes in sensitivity and specificity of the tests with age, plots of sensitivity and specificity in different age groups were displayed graphically. New cutoffs for the FIB-4 and NFS were derived for ≥65-year-old patients by taking the point on the ROC where the combined value of sensitivity and specificity was the highest. As the prevalence of advanced fibrosis can vary in different populations, the PPVs and NPVs for the new cutoffs were displayed at advanced fibrosis prevalence rates of 5, 10, 20, 30, and 40%. A P value of <0.05 was considered significant.

The following data were recorded during the preoperative examination: Sex, age, height, body weight, BMI, smoking history, complete blood count (leukocytes, hemoglobin, platelets), liver function tests (liver enzymes, albumin), renal function tests, preoperative oxygen saturation, history of previous surgery, and concomitant diseases (type 2 diabetes, hypertension, pulmonary and cardiac diseases).
The following data were also collected: History and physical examination findings, chest radiographs, computed tomographic examinations of the chest (CT), electrocardiography (ECG) and echocardiography (if required), pulmonary function test results (forced expiratory volume (FEV1), forced vital capacity (FVC), and FEV1/FVC ratio), and arterial blood gases. In patients with lung cancer, the type and stage of malignancy were determined, and flexible bronchoscopy was performed.
During the intraoperative process, the type of endotracheal tube, the duration of anesthesia and surgery, the surgical procedure (VATS, thoracotomy, mediastinoscopy, and others) performed, and complications that required intraoperative treatment were also noted.
PPCs have been defined as complications that occur in the postoperative period and cause clinical conditions.