Mr. Sixpack is taking a medication that is normally excreted from the body in the urine. His blood work is indicating that the concentration of this medication in his plasma is much higher than normal. This would cause concern that his kidney function has been reduced. The major function of the kidneys is to remove waste products and excess fluid from the body. These waste products and excess fluid are removed through the urine. The production of urine involves highly complex steps of excretion and re-absorption. This process is necessary to maintain a stable balance of body chemicals. {1}

    The critical regulation of the body's salt, potassium, and acid content is performed by the kidneys. The kidneys also produce hormones that affect the function of other organs. For example, a hormone produced by the kidneys stimulates red blood cell production. Other hormones produced by the kidneys help regulate blood pressure and control calcium metabolism. {1}

    The kidneys are powerful chemical factories that perform the following functions: remove waste products from the body, remove drugs from the body, balance the body's fluids, release hormones that regulate blood pressure, produce an active form of vitamin D that promotes strong, healthy bones and control the productions of red blood cells. {1}

    Mr. Sixpack has already been diagnosed with kidney disease. However, it seems evident by his decreased glomerular filtration rate and the unusually high level of medication in his plasma that his kidney function has been reduced.  

    The glomerular filtration rate (GFR) is a test used to check how well the kidneys are working. Specifically, it estimates how much blood passes through the glomeruli each minute. Glomeruli are the tiny filters in the kidneys that filter waste from the blood. {2} Mr. Sixpack's GFR of 35 ml/min would suggest that he is in stage 3b of chronic kidney disease which is catagorized by a range of an estimated GFR between 30 and 44. Many people with stage 3 kidney disease do not have any symptoms. If there are symptoms, there may be: swelling in the hands and feet, back pain and urinating more or less than normal.  At this stage, one is more likely to have health complications as waste builds up in the body, and the kidneys are not working well, such as: high blood pressure, anemia, and bone disease. {3}

References:

{1}  How Your Kidneys Work, National Kidney Foundation, (Date of publication unknown), https://www.kidney.org/atoz/content/howkidneyswork#:~:text=Here's%20how%20kidneys%20perform%20their,bloodstream%20by%20way%20of%20veins

{2} Glomerular Filtration Rate, MedlinePlus, U.S. National Library of Medicine, 31 July 2020, https://medlineplus.gov/lab-tests/glomerular-filtration-rate-gfr-test/

{3} Stages of Chronic Kidney Disease CKD), American Kidney Fund, 17 June 2020, https://www.kidneyfund.org/kidney-disease/chronic-kidney-disease-ckd/stages-