Diastolic dysfunction with nondilated left atrium.

We appreciate the comments by Dr O’Connell and colleagues on our article published in CHEST 1 describing the cumulative incidence and pretransplant risk factors for post-lung transplant renal dysfunction in adult patients with cystic fi brosis (CF). We agree that serum creatinine concentration alone should not be relied upon solely to assess renal function in CF because of its poor sensitivity. Although the use of glomerular fi ltration rate (GFR) estimating equations, such as the Cockcroft-Gault formula and the abbreviated Modifi ed Diet in Renal Disease (aMDRD) equation, represent improvements compared with serum creatinine alone, as they factor in patient age, weight, and sex, these equations still tend to overestimate renal function in CF compared with gold standard measurement techniques. 2 Patients with CF tend to be malnourished compared with the general population, with less muscle mass per body weight. Low muscle mass leads to reduced creatinine pro duction, which results in overestimation of GFR. 3 The estimated 2-year cumulative incidence of post-lung transplant renal dysfunc tion of 35% derived in our study is conservative, since we used the Cockcroft-Gault formula and have likely overestimated renal func tion. Future studies are required to identify more sensitive markers of renal function with less reliance on serum creatinine. We also agree that patients with CF have several unique risk factors for the development of renal dysfunction posttransplant, which may increase their risk relative to patients with idiopathic pulmonary fi brosis or COPD. However, we are not aware of any studies that have specifi cally compared the risk of renal dysfunction in these recipient populations. Our study did not focus on post-lung transplant risk factors, but we appreciate Dr O’Connell and colleagues pointing out that oxalate nephropathy and pigmented tubulopathy are well-recognized histopathologic fi ndings following renal biopsy in the early posttransplant period and are likely related to perioperative stressors such as dehydration, hypoxia, and antibiotics. 4 Our analy sis excluded patients diagnosed with renal dysfunction in the fi rst month post-lung transplant to reduce the chance of includ ing acute cases. Our study found that CF-related diabetes requir ing insulin is an important pretransplant risk factor and likely plays an important role in renal function loss in the late posttransplant period. This is in keeping with a published renal biopsy series, which dem onstrated that histopathologic fi ndings responsible for late epi sodes of renal function loss were primarily vascular (ie, diabetic glomerulosclerosis). 4