Value of serum uric acid to creatinine ratio in predicting airflow limitation in elderly patients with chronic obstructive pulmonary disease

Objective To assess the value of serum uric acid (UA) to creatinine (Cr) ratio in predicting airflow limitation in elderly patients with stable chronic obstructive pulmonary disease (COPD). Methods One hundred and ten stable COPD patients (COPD group) aged 60 years were enrolled at the Department of Geriatrics of Peking University First Hospital from January 2010 to December 2017. These patients were divided into two subgroups: patients with mild-to-moderate airflow limitation [GOLD stages 1 and 2; forced expiratory volume in one second percent (FEV1%) predicted ≥ 50%, n=71] and those with severe-to-very severe airflow limitation (GOLD stages 3 and 4; FEV1% predicted < 50%, n=39). One hundred and nine elderly patients without COPD were collected as controls in the same period at the same hospital. Age, gender, body mass index (BMI), smoking pack-years, medical history, serum UA, serum Cr, blood glucose, blood lipids, and high-sensitive C-reactive protein (hs-CRP) were compared between the two groups. Factors associated with UA/Cr ratio were analyzed by Spearman′s rank correlation and stepwise multivariate analysis. Receiver operating characteristic (ROC) curve analysis was performed to assess the value of UA/Cr ratio in predicting airflow limitation in elderly patients with stable COPD. Results Age, gender, BMI, the percentage of patients with hypertension or diabetes mellitus, Cr, blood glucose, and blood lipids were comparable between the two groups. Smoking index [21 (0, 150) pack-years vs 0 (0, 80) pack-years, Z=-7.014, P<0.001], the percentage of patients with coronary heart disease (47.3% vs 28.4%, χ2=8.250, P=0.004), serum UA level [(355.41±77.13) μmol/L vs (319.30±61.25) μmol/L, t=-3.834, P<0.001], UA/Cr ratio [3.82±0.74 vs 3.45±0.63, t=-4.052, P<0.001], and hs-CRP [1.32 (0.01, 14.70) mg/L vs 0.50 (0.00, 5.50) mg/L, Z=-5.311, P<0.001] were significantly higher in the COPD group than in the control group. Serum UA [(389.49±82.79) μmol/L vs (336.69±67.38) μmol/L, t=-3.620, P<0.001] and UA/Cr ratio (4.15±0.72 vs 3.64±0.70, t=-3.585, P=0.001) were significantly higher in patients with severe-to-very severe airflow limitation than in patients with mild-to-moderate airflow limitation. Spearman′s rank correlation analysis showed that age and FEV1% predicted were negatively correlated with UA/Cr ratio (r=-0.196, P=0.041; r=-0.337, P<0.001, respectively). Stepwise multivariate analysis showed that, using UA/Cr ratio as the dependent variable, FEV1% predicted was associated with increased UA/Cr ratio (β=-0.010, t=-3.029, P=0.003). ROC analysis showed that the area under the ROC curve of UA/Cr ratio for predicting severe-to-very severe airflow limitation was 0.70 (P=0.001). Conclusion UA/Cr ratio has significant predictive value for airflow limitation in elderly patients with COPD. Key words: Chronic obstructive pulmonary disease; Serum uric acid to creatinine ratio; Airflow limitation