In 2002, the National Kidney Foundation published treatment guidelines that identified five stages of Chronic Kidney Disease (CKD) based on declining GFR measurements. The guidelines recommend different actions based on the stage of kidney disease.
CSV (Comma Separated Value) was a file format devised to store tabular data. It uses commas to separate each entry in a row and the newline symbol to go to the next row. Excel is a more recent spreadsheet application from Microsoft and it saves the data with its own file format.
The comma-separated values (CSV) format is a widely used text file format often used to exchange data between applications. It contains multiple records (one per line), and each field is delimited by a comma. Wikipedia has a good explanation of the CSV format and its history. There is no definitive standard for CSV, however the most commonly accepted definition is RFC 4180 - the MIME type definition for CSV. Super CSV is 100% compliant with RFC 4180, while still allowing some flexibility where CSV files deviate from the definition.