Improving outcomes for chronic kidney disease (CKD) requires early identification and recognition by physicians. There are few data on rates of testing or use of diagnostic codes for CKD. A cross-sectional analysis was performed of patients who were older than 40 yr and had one or more laboratory tests between April 1, 2002, and March 31, 2003, at a Laboratory Corporation of America regional laboratory. Objectives were to determine the frequency of testing for serum creatinine; prevalence of CKD, defined as estimated GFR <60 ml/min per 1.73 m2; and sensitivity of diagnostic codes for CKD for patients with and without risk factors for CKD and with or without cardiovascular disease (CVD). Of the 277,111 patients, 19% had serum creatinine measured, compared with 33 and 71% who had measurements of serum glucose and lipids, respectively. Patients with hypertension, diabetes, and age >60 yr were more likely to be tested for serum creatinine with odds ratio (OR; 95% confidence interval) of 2.09 (2.05 to 2.14), 1.22 (1.19 to 1.25), and 1.24 (1.22 to 1.27) respectively. Among patients tested, 30% had CKD. Sensitivity and specificity of kidney disease diagnostic codes compared with CKD defined by estimated GFR <60 ml/min per 1.73 m2 were 11 and 96%, respectively. In patients with hypertension, diabetes, age >60 years, and CVD, rates of testing and sensitivity of diagnostic codes were 53 and 14%, respectively. Low rates of testing for serum creatinine and insensitivity of diagnostic codes for CKD, even in high-risk patients, suggests inadequate physician awareness of CKD and limited utility of administrative databases for identification of patients with CKD.