The Central Biochemistry Laboratory (CBL) has assumed a key leadership position in the renewal of the Prospective Study of Chronic Kidney Disease in Children (CKiD). The CBL is responsible for providing participating clinical sites with the reagents, supplies, shippers and protocols needed for performing iohexol- based glomerular filtration rate (GFR) studies and transporting blood to the University of Rochester laboratory for analysis of key kidney determinants, including Cr, BUN, electrolytes, glucose, Ca, P, intact PTH, vitamin D, wrCRP, lipid screen, and cystatin C. Similarly, urine is collected and transported for protein, creatinine, and microalbumin to assess the nature of kidney damage. The CBL also provides reagents, shippers, and instructions to all participating sites for submission of blood, plasma, sera, urine, hair and nail samples to NIH repositories. In conjunction with the Clinical Coordinating Centers, the CBL provides training of coordinators and investigators of each participating site, information and instruction concerning the conduct of each study visit, expertise in the biochemical methodology and clinical interpretation of these analyses. The CBL collaborates with the Data Coordinating Center (DCC) to optimize the GFR studies, better understand the progression of chronic kidney disease, provide clinical correlation with epidemiological projections, establish quality control of all assays, and generate new formulas to estimate GFR during visits when an iohexol study is not performed. The CBL regularly participates at Steering Committee meetings and conference calls as well as in the generation of abstracts, presentations, and manuscripts in order to contribute to and document the success of the CKiD study. The CBL's effort in the CKiD study is summarized in five specific aims. First, continue to provide accurate, precise, and most efficient measures of iohexol-based GFR, because it is the key independent variable against which measures of growth, cardiovascular disease, and neurocognition are examined. Second, continue to provide accurate and precise measurements of general kidney health status, utilizing biochemical assays in a licensed clinical laboratory with appropriate quality controls. Third, work closely with the DCC to provide accurate estimates of GFR and determine time-dependent changes in GFR during visits when iohexol GFR is not performed. Fourth, continue to improve and streamline the iohexol-based GFR measurement to maintain recruitment and retention of CKiD subjects. Fifth, continue to provide to the participating clinical sites laboratory kits for the collection and handling of samples, accurately receive, process, and analyze these samples on a daily basis, and provide timely data entry into the CKiD web-based data base for access by the participating clinical sites, Clinical Coordinating Centers, and Data Coordinating Center. The long term goal is to provide accurate assays to characterize the CKiD population and maintain recruitment and retention of CKiD subjects.