Background: Although the cardiorenal relationship in chronic kidney disease has been investigated, information about the lung-kidney relationship is limited. Here, we investigated the impact of kidney function and urinary protein excretion on pulmonary dysfunction.
Methods: The data from pulmonary function tests and kidney function (estimated glomerular filtration rate [eGFR] and urinary protein) between 1 April 2005 and 30 June 2010 were selected from our laboratory database. Data were classified into 4 categories according to eGFR and proteinuria. Category 1, eGFR ≥60 ml/min/1.73 m(2) and urinary protein <0.3 g/gCr; category 2, eGFR <60 ml/min/1.73 m(2) and urinary protein <0.3 g/gCr; category 3, eGFR ≥60 ml/min/1.73 m(2) and urinary protein ≥0.3 g/gCr; and category 4, eGFR <60 ml/min/1.73 m(2) and urinary protein ≥0.3 g/gCr. Pulmonary function data were evaluated according to these 4 categories.
Results: A total of 133 participants without major respiratory disease, abnormal computed tomography and smoking history were enrolled. Hemoglobin (Hb)-adjusted percentage carbon monoxide diffusing capacity (%DLCO) in category 4 (46.2 ± 7.5) and category 2 (63.6 ± 17.8) were significantly lower than in category 1 (75.8 ± 18.9) (P < 0.05). In addition, Hb-adjusted %DLCO was weakly correlated with eGFR in participants with urinary protein <0.3 g/gCr (R = 0.30, P = 0.001). Hb-adjusted %DLCO was strongly correlated with eGFR in participants with urinary protein ≥0.3 g/gCr (R = 0.81, P < 0.001). Other pulmonary function test markers (percentage (%) vital capacity, % forced expiratory volume in one second (FEV1), FEV1/forced vital capacity, % total lung capacity, and % residual volume) were not significantly different between categories.
Conclusion: This study suggests that decreased eGFR is associated with decreased %DLCO in proteinuric patients.