Chronic Kidney Disease (CKD)
Definition: Chronic kidney disease (CKD) is the presence of kidney damage or decreased kidney function for > 3 months. (<3 months is considered acute kidney disease.)
Nephron: each individual functional unit of the kidney, consisting of a glomerulus (the renal corpuscle–a tuft of capillaries) and its associated tubule.
Glomerular Filtration Rate (GFR): Kidney function is determined by glomerular filtration rate, which is a sum of the function of all working nephrons. The fewer the number of functioning nephrons, the lower the GFR and the more disease is present. GFR is merely a gauge to classify degrees of kidney dysfunction:
- Normal GFR is 125 mL/min/1.73 m2 (filtered blood per minute as applied to body size/area)
- Chronic kidney disease is a GFR < 60 (mL/min/1.73 m2)
- Kidney failure is a GFR or < 15 (mL/min/1.73 m2)
Kidney damage refers to structural or functional abnormalities other than a decreased GFR, such as
- Glomerular disease from diabetes, autoimmune disease, infection, drug toxicity, or malignancy
- Vascular disease (affecting blood supply to the kidneys) from atherosclerosis, hypertension, ischemia, or vasculitis
- Tubular disease (kidney tubules disease), from infections, stones, obstruction, or drug toxicity
- Congenital abnormality of the anatomy (e.g., polycystic kidney disease)
Signs and Symptoms of CKD
- Edema (swelling)
- Decreased urine output (“oliguria”)
The body’s biochemical reactions all work best at an ideal pH (measurement of acidity/alkalinity due to urinary excretion of the daily acids accrued through normal metabolism). When the kidney falters in this task, the acids are not eliminated efficiently and the blood becomes more acid (acidotic, or a lowering of pH). Compensatory mechanisms (excretion of ammonium) fail when GFR falls below 40-50 mL/minute. Chronic acidosis from chronic kidney disease results in bone resorption (osteopenia), muscle protein breakdown, hyperparathyroidism, impaired cardiac muscle/heart failure, insulin resistance (diabetes), and hypotension.
Clinical Course of CKD
With progressive failure, the dysfunction in CKD and its acidosis can eventually reach a point at which either physiological or medical compensation is no longer enough to be compatible with life, and at this point–called “end-stage renal failure”(ESRF)–either dialysis or kidney transplant is necessary.