Study On Clinical Correlation Between Serum Vitamin D Level And ILD

Objective:To evaluate vitamin D levels in patients with ILD,and to further explore whether low levels of vitamin D have clinical significance for the treatment and prognosis of ILD.Methods:A retrospective analysis was conducted to compare 207 cases of ILD initially diagnosed in department of Respiratory and Critical Care Medicine,Affiliated Hospital of Qingdao University from September 2020 to September 2021.Patients with ILD were divided into connective tissue associated interstitial lung disease group（CTD-ILD）,interstitial pneumonia with autoimmune features group（IPAF）,and idiopathic interstitial pneumonia group（IIP）.Vitamin D levels were assessed by measuring 1,25（OH）₂D₃.The basic information and data,laboratory parameters and imaging examination（HRCT）results of all patients were recorded.Statistical analysis was performed by SPSS 25.0.Pearson correlation was used to analyze the correlation between serum vitamin D level and lung function,blood gas analysis and other indicators.Linear regression analysis was used to further illustrate the correlation between serum vitamin D and related variables.Calculate the critical value and draw the ROC curve.Result:1.Vitamin D levels in CTD-ILD group and IPAF group were significantly lower than those in healthy control group,P<0.05.There was no significant difference in vitamin D levels between the IIP group and the healthy control group.Compared with the IPAF group,the CTD-ILD group had lower serum vitamin D,forced vital capacity（FVC）,diffusing capacity of the lung carbon monoxide（DLCO）,serum calcium levels,faster erythrocyte sedimentation rate,higher interleukin-6（IL-6）levels,and higher CPI.The difference between the two groups was significant,P<0.05.2.CTD-ILD group:（1）Pearson correlation analysis showed that there was a significant difference between serum level of vitamin D and Oxygen partial pressure（PO2）（r=0.344）,carbon dioxide partial pressure,（PCO2）（r=0.317）,oxygenation index（r=0.344）,lactate（r=-0.249）,fasting blood glucose（r=0.250）,pulmonary artery pressure（r=-0.394）,Total lung capacity（TLC）（r=0.447）,six-minute walk distance（r=0.626）,Forced Expiratory Volume Per Second（FEV₁）（r=0.654）,forced vital capacity（FVC）（r=0.625）,DLCO（r=0.822）,m MRC（r=-0.661）,CPI（r=-0.720）.（2）One-variable linear regression showed that serum level of vitamin D was positively related to PO2,PCO2,oxygenation index,fasting blood glucose,TLC,six-minute walking distance,FEV₁,FVC,DLCO;was negatively related to lactate,pulmonary artery pressure,CPI.Multiple linear regression showed that serum level of vitamin D was positively related to six-minute walking distance,FVC,DLCO,R²=0.714,P<0.05.（3）According to the ROC curve analysis of serum vitamin D level in CTD-ILD group,when you took the maximum value of Youden index as 0.484,the area under curve（AUC）was 0.705（95%CI:59.68%-81.29%）,P<0.001,the cut-off was 14.55,the sensitivity was 0.759,the specificity was 0.725.3.IPAF group:（1）Pearson correlation analysis showed that there was no significant difference between serum level of vitamin D and D-dimer,IL-6,CD4 cell absolute count,PCO₂,lactate,fasting blood glucose,serum calcium,and creatinine levels（P>0.05）.It was positively correlated with BMI（r=0.265）,oxygen saturation（r=0.327）,TLC（r=0.357）,PO₂（r=0.580）,oxygenation index（r=0.580）,six-minute walking distance（r=0.507）,FEV₁（r=0.537）,FVC（r=0.580,P<0.01）,DLCO（r=0.686）.Serum level of vitamin D were negatively correlated with FEV₁/FVC（r=-0.373）,pulmonary arterial pressure（r=-0.367）,erythrocyte sedimentation rate（r=-0.587）,m MRC（r=-0.588）and CPI（r=-0.827）.（2）One-variable linear regression showed that serum level vitamin D was positively related to BMI,oxygen saturation,TLC,PO₂,oxygenation index,six-minute walking distance,FEV₁,FVC,DLCO;was negatively related to ESR,FEV₁/FVC,m MRC,CPI.Multiple linear regression showed that serum level of vitamin D was positively correlated with 6-minute walking distance and DLCO（R²=0.542,P<0.05）.4.CTD-ILD follow-up group:The serum level of vitamin D,FEV₁,FVC,and DLCO were increased at the end point of observation.Serum level of vitamin D were significantly positively correlated with FEV₁,FVC,and DLCO（P<0.01）.Conclusions:1.Serum level of vitamin D in patients with CTD-ILD and IPAF are lower than normal.It is not reduced in IIP patients.CTD-ILD patients have lower serum level of vitamin D,FVC,DLCO,serum calcium,faster erythrocyte sedimentation rate,and higher IL-6 levels than IPAF patients.2.The higher the serum vitamin D level in CTD-ILD patients,the higher the patients’FEV₁,FVC and DLCO.After vitamin D treatment,lung function could improve as serum vitamin D levels increase.3.The ROC curve critical value analysis of serum vitamin D level predicting adverse prognosis found that when serum vitamin D level is 14.55ng/m L,the adverse prognosis of CTD-ILD patients could be better predicted with the corresponding AUC value of 0.705,sensitivity of 0.759,and specificity of 0.725.These results suggest that vitamin D may be a sensitive indicator of disease progression in patients with CTD-ILD.4.The lower the serum vitamin D levels of patients with IPAF,the lower the 6-minute walking distance and DLCO level of patients.It suggests that the serum vitamin D level is related to the lung function impairment and disease severity of patients with IPAF.