1) Blood And Urine Test Indications: A doctor will test kidney function with simple blood and urine lab tests. These are the most important and reliable indicators of kidney function and may indicate loss of kidney function before any other symptoms have appeared – hence put at the top of the list despite requiring a lab test. The blood test measures creatinine, which is a breakdown product of muscle metabolism. Higher levels of creatinine indicate a lower glomerular filtration rate (GFR, eGFR or estimated GFR) – which indicates how well your kidneys are filtering and excreting waste products. GFR of 90-120 is considered normal. GFR below 60 indicates chronic kidney disease. A GFR below 15 indicates kidney failure.
Creatinine levels may register as normal in early stages of chronic kidney disease, but kidney disease can be detected if urine testing shows the kidney is allowing a protein called albumin to escape into the urine.  Albumin is not typically detected in urine in healthy kidney function.
2) Blood In Urine: This is a definite reason for a visit to the doctor. Note also that there may be small amounts of blood in the urine that are not sufficient to change the color of the urine, that can only be detected by medical testing – so it’s important to have your regular medical checkups as this may detect trace blood in the urine before it becomes more serious.