Please choose the correct ending to complete the given sentence: Health: [header] How to increase gfr [title] Take the test. [step] Your doctor can test your gfr by administering a creatinine blood test. Creatinine is a waste product present in your blood.

Ending1: While it is produced by your cells, it is linked to your own electrical processes, such as electric current running through certain systems. If your body functions normally normally, the test will no longer be necessary. Ending2: To successfully test your gfr, urinate or drink water or try muscle exercises. Exercises won't work and the test will take up to 15 minutes to complete. Ending3: If the amount of creatinine contained within a sample is too high, your kidneys' filtering ability (gfr) is likely too low. [substeps] Alternatively, your doctor might administer a creatinine clearance test, which measures the amount of creatinine in both your blood and urine. Ending4: Because it is harmless, it won't do anything to your gfr. For example, the test won't detect ketones in your liver, but that may be why gfr tests are necessary.

Answer format: ending1/ending2/ending3/ending4