Study design and participants
In this prospective cross-sectional study, CF patients enrolled in the current study were clinically stable CF adults with CFTR I1234V mutation attending adult CF clinics as routine care at Hamad Medical Corporation (HMC), Doha, Qatar. The diagnosis of CF was made on one or more phenotypic features consistent with CF, positive family history of CF in siblings and close relatives, confirmed by elevated the concentration of sweat chloride (> 60 mmol/l) on two different occasions and CF genetic testing.
Inclusion criteria included all CF patients ≥ 18 years old, who were able to expectorate sputum and free of active infections for more than 4 weeks prior to study enrollment and no acute chest exacerbation among CF patients based on recent definition .
Exclusion criteria included all CF patients who were smoking within the last two months; pregnancy, nursing mothers and CF patients who underwent a lung transplant. Control subjects were recruited from volunteers visiting the hospital with patients who were non-smoker and free from acute infection during the 4 weeks preceding the study.
Study measures and data variables
Bodyweight was recorded using an electronic platform scale and standing height measurement using a stadiometer. BMI was computed by dividing weight in kg by the height squared in meters. Clinical data were obtained from CF subjects; sputum was collected for microbiology per CF consensus guidelines . All CF subjects perform spirometry tests in the respiratory laboratory
unit in accordance with the guidelines f the American Thoracic Society . The best recorded forced expiratory volume in 1 second (FEV1) using Spiro bank, MIR, Italy. The maximum of three appropriate measurements is recorded with < 15% variation. Forced vital capacity (FVC; in liters), forced expiratory volume in 1second (FEV1; in liters,), FEV1/FVC (in %) are measured and expressed as a percent of predicted normal using standard equations .
Pancreatic insufficiency was defined as those with low fecal elastase level and required daily pancreatic enzyme supplementation with meals and snacks.
Measurement of adiponectin in plasma and sputum samples: The plasma and sputum were collected from each CF patient while for the control subjects only plasma was collected for adiponectin measurement. Plasma and sputum adiponectin levels were measured using Bio-Plex Pro Human Diabetes Adiponectin Assay (Cat # 171a7003m). All samples were assayed in duplicate. The lower limit of detection with the adiponectin assay was 171 pg/ml. The Intra-assay coefficients of variation were 4% and inter-assay coefficients of variation was 2%.
Data are presented as mean ± standard deviation (SD) or median (quartile range) for data with a skewed distribution. Categorical data values were expressed as frequencies (percentages). Differences in their mean values between CF patients and healthy controls were compared using unpaired Student's t-test and Mann–Whitney U test for skewed data distribution. Associations between two or more categorical variables (gender, CF patients and healthy controls) were examined using Chi-square (χ2) test or Fisher Exact test as appropriate.
Pearson’s correlation was applied to assess the strength of the linear relationship between two or more quantitative variables (to evaluated baseline concentrations of sputum and serum adiponectin, in the of CF patients and assess the relationship to FEV1 %, FVC %, FEV1/FVC and BMI). Key findings presented using appropriate statistical graphs (scatter and Box plots). All P values presented were two-sided, and P values <0.05 was considered as statistically significant. All Statistical analyses were done using statistical packages SPSS 23.0 (SPSS Inc. Chicago, IL) and Epi-info (Centers for Disease Control and Prevention, Atlanta, GA) software.