[Characteristics and clinical significance of pulmonary function test and KL-6 in ASSD-ILD and IPF]

Objective: To study the characteristics and clinical significance of pulmonary function test and kerbs von den lungen 6 (KL-6) in anti-synthetase syndrome related interstitial lung disease (ASSD-ILD) and idiopathic pulmonary fibrosis (IPF). Methods: The clinical data of 43 patients with ASSD-ILD (ASSD-ILD group) from May 2015 to May 2017 were collected retrospectively, including 12 males and 31 females, and 34 patients with IPF (IPF group) treated in the First Affiliated Hospital of Zhengzhou University during the same period, including 28 males and 6 females, were also included. The basic information, and the value of pulmonary function test [pulmonary function parameters included the forced vital capacity expressed as percent predicted (FVC%pred), the forced expiratory volume in 1 second expressed as percent predicted (FEV(1)%pred), the ratio of FVC to FEV(1) (FVC/FEV(1)), the peak expiratory flow expressed as percent predicted (PEF%pred), the forced expiratory flow at 25%, 50%, 75% of FVC as percent predicted (FEF(25)%pred, FEF(50)%pred, and FEF(75)%pred), the maximum mid-expiratory flow as percent predicted (MMEF% pred), and the diffusing capacity for carbon monoxide as percent predicted (DLCO% pred)], and serum KL-6 level in ASSD-ILD and IPF were compared. Results: The FEV(1)%pred, FEF(50)%pred, FEF(75)%pred, and MMEF%pred values in ASSD-ILD group were significantly lower than those in IPF group (all P<0.05), while the FVC% pred, FVC/FEV(1), PEF% pred, FEF(25)%pred, and DLCO% pred values in ASSD-ILD group had no significant difference compared with IPF group (all P>0.05). There was no significant difference in serum KL-6 level between ASSD-ILD group and IPF group [(1 169±911) vs (1 210±908) U/ml, t=0.62, P=0.463]. Follow-up analysis showed that the serum KL-6 level of ASSD-ILD patients who died within two years was significantly higher than that of survivors [(2 060±1 168) vs (1 042±858) U/ml, t=2.93, P=0.041]. The serum KL-6 level of patients who died within two years of IPF patients was also significantly higher than that of patients who survived [(1 767±865) vs (1 089±894) U/ml, t=2.53, P=0.026]. The serum KL-6 level in ASSD-ILD group was negatively correlated with FVC%pred (r=-0.43, P=0.004), FEV(1)%pred (r=-0.39, P=0.010) and DLCO% pred (r=-0.41, P=0.006). There was no correlation between serum KL-6 level and pulmonary function test indexes in IPF group (all P>0.05). Conclusions: There is difference in pulmonary function test between ASSD-ILD patients and IPF patients. High serum KL-6 level will be predictive of poor prognosis.