Chronic Kidney Disease Basics for the Physician Assistant Exam
For both the Physician Assistant Exam and in practice, you need to be aware of the stages of chronic kidney disease, issues with anemia and bone health, and indications for dialysis.Chronic kidney disease (CKD) is a significant health problem in the United States. More than 31 million people have been diagnosed with chronic kidney disease, and the problem is getting worse.
The stages of chronic kidney disease
Chronic kidney disease has six stages, each more advanced than the previous one:
Stage I means that the glomerular filtration rate (GFR) is okay but proteinuria is present. Even if the kidney function is normal, someone can have early stage kidney disease just by having proteinuria.
Stage II means mild kidney disease with a GFR of 60–89 mL/min.
Stage III refers to moderate kidney disease. The GFR is 30–59 mL/min. At this stage, you usually begin to see abnormalities in blood and bone metabolism.
Stage IV is advanced kidney disease with a GFR of 15–29 mL/min.
Stage V is advanced kidney disease with a GFR of 15 mL/min or less.
At Stage VI, someone is on or needs to start dialysis.
Test questions often ask absolute indications for dialysis, which include the following:
Fluid overload refractory to diuretic therapy
A positive pericardial friction rub, which is suggestive of uremic pericarditis
Very high potassium with ECG changes
A toxic ingestion of a substance removed by dialysis; examples include lithium and the toxic alcohols (ethylene glycol, methanol, and rubbing alcohol)
At which stage of chronic kidney disease (CKD) should a patient be seen for transplant evaluation and discussion regarding placement of permanent access for dialysis?
(A) Stage I
(B) Stage II
(C) Stage III
(D) Stage IV
(E) Stage V
The answer is Choice (D), Stage IV. Obtaining a transplant evaluation and obtaining a permanent access for dialysis (a fistula) are things that should be done at this stage of kidney disease. The first three stages are too early, and the last one is too late.
How kidney disease affects the blood and the bones
Kidney disease, unfortunately, doesn’t exist in a vacuum; it affects the bones and the blood, too. A major cause of anemia in kidney disease is due to the kidney’s decreased production of erythropoietin. You begin to see reductions in blood hemoglobin levels as early as Stage III chronic kidney disease.
Here are some test-taking points concerning anemia in chronic kidney disease:
Other causes of anemia other than the decreased production of erythropoietin in chronic kidney disease include the three i’s: iron deficiency, inflammation (which can have a direct suppressive effect on the bone marrow), and infection.
If the hemoglobin level is < 10 mg/dL, erythropoietin stimulating agents (ESA) are prescribed.
Recognize that iron levels need to be adequate for ESAs to work. Iron deficiency is the most common cause of ESA resistance. The iron can be given intravenously or orally.
Concerning bone changes, you can begin to see changes consistent with secondary hyperparathyroidism as early as Stage III. Bone disease in chronic kidney disease is important not just from a bone perspective — elevated parathyroid hormone levels can have adverse effects on other organs, including the heart. In addition to an elevated PTH level, other changes include an elevated phosphorous level. In advanced stages, you might see low calcium levels.
Here are some test-taking points concerning bone disease in chronic kidney disease:
The pattern of secondary hyperparathyroidism in chronic kidney disease is high phosphorous, low calcium, and elevated intact PTH.
For Stage III chronic kidney disease and higher, many patients are prescribed a low-phosphate diet and phosphate binders to bind dietary phosphorous in the intestine.