Renal Function

We have two kidneys, located in the flank (retroperitoneum) which act like filters or sieves.  The sieve filters the waste products from cellular metabolism, and any extra water for excretion as urine.  Routine chemical analysis of the blood provides several tests to monitor the effectiveness of the filter.  Blood urea nitrogen (BUN) and creatinine (CR) gauge the function of the filtering process.  When BUN and CR are elevated, the kidneys are unable to maintain their job of keeping impurities and toxins out of the blood.  A more important test is the glomerular filtration rate (eGFR), which measures the rate the urine is being produced.  eGFR decreases as renal function declines.  As BUN and CR rise, and eGFR decreases, the kidney function can be described as renal insufficiency (RI) or even chronic renal failure (CRF).  Another telling sign in deteriorating kidney function is protein in the urine.  Protein is a very large molecule; the kidney has holes or spaces in the sieve to excrete such a large molecule.  Sort of like a green pea that slips through the sieve when you strain your vegetables for dinner.  A smaller protein is known as microalbumin and indicates an early stage of a leaking filter.

​If renal function continues to decline due to diseases such as complications from diabetes, nephrosclerosis (most common cause), polycystic kidney disease (congenital), end stage renal disease may result (uremia).  End stage renal disease (ESRD) requires an filtering system outside the body, to cleanse the blood from toxins.  Peritoneal dialysis uses the peritoneum (lining of the abdomen) and a cleaning solution (dialysate) to filter the blood.  This type of dialysis is more convenient and can be done at home.  Hemodialysis requires vascular access, usually in the arm, where two needles will be used for each session, one to allow the blood to flow out to the dialysis machine, and one to allow the cleansed blood to flow back in.  The access is called an AV fistula (arterio-venous) and takes several months to prepare.  This type of dialysis requires regular visits to the dialysis center usually lasting several hours. 

Renal transplants were first experimented with in 1902 (in Vienna, with animals).  In 1909 an animal kidney was transplanted into a human.  In 1933 the first human-to-human transplant was performed.  The kidney never functioned because of mismatched donor and recipient blood types; the recipient’s body did not recognize the new kidney and a fatal reaction was unavoidable.  The first successful transplant was performed in 1954 in Boston.  The donor was an identical twin to the recipient thereby avoiding the rejection process.  The recipient lived an amazing eight years.  The advent of anti-rejection drugs (immunosuppressants) has predictably improved renal transplant survival rates.

Between 2001 and 2016 studies showed a reduction in mortality in both types of dialysis and transplants (https://www.uptodate.com/contents/patient-survival-and-maintenance-dialysis).  Survival of dialysis and transplants is impacted by age (over 65), financial and social status and comorbidities.  Inadequate dialysis and length of time on dialysis show a slightly lower survival rate.  With the reduction in mortality, there is a greater demand for matching organs, which will obviously increase time on dialysis.