When you have kidney disease, your kidneys are no longer able to remove waste effectively from your body or to balance your fluids. The build up of wastes can change the chemistry of your body causing some symptoms that you can feel, and others that you don't.
Reference to a range of cells is typically of the form (A1:A6), which specifies all the cells in the range A1 through to A6. A formula such as =SUM(A1:A6) would add all the cells specified and put the result in the cell containing the formula itself.
If a cell is blank, that value will be zero according to Microsoft. You can use the IF function with empty quotes () to test for empty cells. To clarify the formula examples, B2 represents the cell containing the data you want to test. E2 represents the cell in which you enter the formula.