22 Renal Physiology & Dialysis Principles Practice Questions & Answers

1. 1. A patient asks how healthy kidneys can filter such a large volume of plasma every day yet produce only a small volume of urine. Which explanation is correct?

   • A.The glomerulus filters a large volume of plasma, and the tubules reabsorb most of that water and most useful solutes back into the blood✓ Answer
   • B.The glomerulus filters only a few milliliters of plasma, and the bladder manufactures the rest of the urine
   • C.The kidneys store most of the filtered fluid in the renal pelvis and release it slowly over several days
   • D.Most of the filtered fluid is broken down by the liver before it ever reaches the tubules

   Urine formation is a three-step process: glomerular filtration, tubular reabsorption, and tubular secretion. The glomerulus filters an enormous volume of plasma each day, but the tubules return most of that water along with glucose, sodium, and bicarbonate to the blood, so only a small fraction of the filtrate leaves the body as urine.

   Source: Core Curriculum for the Dialysis Technician (Medical Education Institute) — normal kidney structure and functionReport a problem with this question

2. 2. A patient who has been on hemodialysis for two years is persistently pale, tired, and short of breath with mild activity, and the nurse reports a low hemoglobin. Which mechanism of kidney failure best explains this finding?

   • A.The failing kidneys can no longer store the red blood cells the body has already produced
   • B.The failing kidneys produce less erythropoietin, so the bone marrow makes fewer red blood cells✓ Answer
   • C.The dialyzer membrane removes red blood cells along with urea during every treatment
   • D.The failing kidneys destroy vitamin D, and the bone marrow needs vitamin D to build hemoglobin

   Erythropoietin is a hormone made by healthy kidneys that signals the bone marrow to produce red blood cells. When kidney tissue is destroyed, that signal is lost and anemia develops; it is followed with hemoglobin and hematocrit, not with calcium or albumin, and it is treated with an erythropoiesis-stimulating agent plus adequate iron as ordered.

   Source: NNCC CCHT content outline — Clinical: recognize and report signs and symptoms; Core Curriculum for the Dialysis Technician (Medical Education Institute)Report a problem with this question

3. 3. A patient with long-standing kidney failure has bone pain and a low serum calcium. Which loss of normal kidney function best explains the low calcium?

   • A.The kidneys can no longer activate vitamin D, so the intestine absorbs less dietary calcium✓ Answer
   • B.The kidneys can no longer secrete parathyroid hormone, so calcium is not released from bone
   • C.The kidneys can no longer produce erythropoietin, and calcium is carried on red blood cells
   • D.The kidneys can no longer manufacture calcium itself, so the blood level falls

   One of the kidney's endocrine jobs is converting vitamin D to its active form (calcitriol), and calcitriol is what allows the intestine to absorb calcium. Without it, dietary calcium is poorly absorbed and serum calcium falls, which is one of the drivers of renal bone disease. Parathyroid hormone comes from the parathyroid glands, not the kidneys.

   Source: Core Curriculum for the Dialysis Technician (Medical Education Institute) — endocrine functions of the kidney and CKD mineral and bone disorderReport a problem with this question

4. 4. Which statement best explains why patients with kidney failure tend to become acidotic, and how hemodialysis helps correct it?

   • A.Acid builds up because the lungs stop working in kidney failure, and dialysis has no effect on acid-base balance
   • B.Acid builds up because dialysis strips bicarbonate out of the blood by convection
   • C.The failing kidney can no longer excrete hydrogen ion and regenerate bicarbonate, so acid accumulates; bicarbonate then diffuses from the dialysate into the blood during treatment✓ Answer
   • D.The failing kidney makes too much bicarbonate, and dialysis removes the excess by ultrafiltration

   Healthy kidneys maintain acid-base balance by excreting hydrogen ion in the urine and regenerating bicarbonate buffer. When that function is lost, metabolic acidosis develops. Dialysate contains bicarbonate at a higher concentration than the acidotic patient's blood, so bicarbonate diffuses down its concentration gradient into the blood and restores buffer.

   Source: Kallenbach, Review of Hemodialysis for Nurses and Dialysis Personnel — acid-base balance and dialysate compositionReport a problem with this question

5. 5. Hypertension is very common among patients with kidney failure. Which combination of lost kidney functions best explains it?

   • A.Loss of erythropoietin production, which normally keeps the arteries relaxed
   • B.Loss of vitamin D activation, which normally lowers blood pressure by widening the arteries
   • C.Loss of the ability to excrete sodium and water, combined with abnormal renin release that raises vessel tone✓ Answer
   • D.Loss of the kidney's role in producing white blood cells, which normally regulate blood pressure

   The kidney controls blood pressure two ways: by regulating extracellular volume through sodium and water excretion, and hormonally through the renin-angiotensin-aldosterone system. In kidney failure both are disturbed, so retained volume plus inappropriate vasoconstriction produce hypertension. This is why interdialytic weight gain and blood pressure track together.

   Source: Core Curriculum for the Dialysis Technician (Medical Education Institute) — blood pressure regulation by the kidneyReport a problem with this question

6. 6. Within the nephron, which structure reabsorbs sodium chloride and is chiefly responsible for concentrating the urine?

   • A.The ureter
   • B.The glomerulus
   • C.The renal capsule
   • D.The loop of Henle✓ Answer

   The nephron is the functional unit of the kidney and consists of a glomerulus plus a tubule. Filtration occurs at the glomerulus; the loop of Henle then reabsorbs sodium chloride and creates the concentration gradient in the kidney's medulla that allows urine to be concentrated. The renal capsule is a covering and the ureter simply carries urine to the bladder.

   Source: Core Curriculum for the Dialysis Technician (Medical Education Institute) — anatomy of the nephronReport a problem with this question

7. 7. Between treatments a patient reports loss of appetite, nausea, a metallic taste, and generalized itching. The technician recognizes these as symptoms of uremia. Uremia is best described as:

   • A.An infection of the urinary tract that has spread into the bloodstream
   • B.The build-up in the blood of waste products that healthy kidneys would normally excrete in the urine✓ Answer
   • C.A deficiency of oxygen-carrying red blood cells
   • D.An excess of bicarbonate buffer in the blood

   Uremia literally means urine in the blood: nitrogenous wastes such as urea, creatinine, and uric acid accumulate because the kidneys can no longer excrete them, and those retained products cause the fatigue, anorexia, nausea, metallic taste, itching, and mental changes the patient describes. A deficiency of red cells is anemia, a separate consequence of kidney failure.

   Source: NNCC CCHT content outline — Clinical: recognize and report signs and symptoms of uremiaReport a problem with this question

8. 8. A patient who missed the previous treatment arrives complaining of muscle weakness and tingling around the mouth. The technician knows potassium accumulates between treatments in kidney failure. Why is potassium the electrolyte of most immediate concern?

   • A.A high potassium level makes bones brittle over many years, so it can be raised at the next monthly review
   • B.A high potassium level thins the blood and causes prolonged bleeding at the needle sites
   • C.A high potassium level causes itching, which is uncomfortable but not dangerous
   • D.A high potassium level can disturb the heart's electrical conduction and cause a life-threatening arrhythmia, so these findings must be reported to the nurse at once✓ Answer

   Potassium is normally excreted by the kidney, so in kidney failure it rises between treatments, especially after a missed session. Because potassium governs the electrical activity of cardiac muscle, a high level can produce peaked T waves, arrhythmia, and cardiac arrest. Muscle weakness and paresthesias are warning signs that the technician reports to the nurse immediately rather than acting on independently.

   Source: NNCC CCHT content outline — Clinical: recognize and report signs and symptoms; Core Curriculum for the Dialysis Technician (Medical Education Institute)Report a problem with this question

9. 9. A patient arrives with ankle edema, shortness of breath when lying flat, and a blood pressure higher than usual. Which mechanism of kidney failure best accounts for this picture?

   • A.The kidneys can no longer produce erythropoietin, so fluid leaks out of the capillaries
   • B.The kidneys can no longer activate vitamin D, which draws water into the lungs
   • C.The kidneys deliberately secrete extra water into the tissues to protect the heart
   • D.The kidneys can no longer excrete the sodium and water taken in, so the excess volume expands the vascular and tissue spaces✓ Answer

   Fluid balance depends on the kidney's ability to excrete the sodium and water a person takes in. When that ability is lost, the retained volume distributes into the bloodstream and interstitial tissue, producing edema, hypertension, shortness of breath, and, if severe, pulmonary edema and heart strain. The technician reports these findings so the nurse can reassess the fluid removal plan.

   Source: Kallenbach, Review of Hemodialysis for Nurses and Dialysis Personnel — fluid volume overload in kidney failureReport a problem with this question

10. 10. A long-term patient has a high serum phosphorus, a low serum calcium, and an elevated parathyroid hormone level. Which chain of events explains this pattern?

    • A.Loss of erythropoietin raises phosphorus and lowers calcium, and parathyroid hormone rises to protect the bone
    • B.The failing kidney cannot excrete phosphorus and cannot activate vitamin D, so phosphorus rises and calcium absorption falls; the parathyroid glands respond by releasing more hormone, which weakens bone✓ Answer
    • C.Dialysis adds phosphorus to the blood by diffusion, and the parathyroid glands shut down in response
    • D.The failing kidney excretes too much phosphorus, and the parathyroid glands respond by blocking calcium in the diet

    Two failures act together in renal bone disease: phosphorus is retained because it can no longer be excreted, and calcitriol is no longer produced, so intestinal calcium absorption falls. The resulting high phosphorus and low calcium stimulate the parathyroid glands, and the sustained rise in parathyroid hormone pulls calcium out of bone. This is why phosphate binders are taken with meals and vitamin D analogs are prescribed for bone health.

    Source: Core Curriculum for the Dialysis Technician (Medical Education Institute) — CKD mineral and bone disorderReport a problem with this question

11. 11. Which option correctly pairs a substance that ACCUMULATES in kidney failure with a substance that becomes DEFICIENT?

    • A.Potassium accumulates; erythropoietin becomes deficient✓ Answer
    • B.Bicarbonate accumulates; phosphorus becomes deficient
    • C.Erythropoietin accumulates; potassium becomes deficient
    • D.Urea becomes deficient; activated vitamin D accumulates

    Kidney failure produces two kinds of problems at once. Substances the kidney should excrete build up: urea and other nitrogenous wastes, potassium, phosphorus, hydrogen ion, and water. Substances the kidney should make or activate run short: erythropoietin, activated vitamin D, and the bicarbonate it normally regenerates. Sorting any finding into one of those two lists explains most of the clinical picture.

    Source: Kallenbach, Review of Hemodialysis for Nurses and Dialysis Personnel — consequences of kidney failureReport a problem with this question

12. 12. A patient dialyzed for many years develops carpal tunnel symptoms and joint pain attributed to retention of beta-2 microglobulin, a middle-sized molecule. Which transport mechanism is chiefly responsible for removing molecules of that size?

    • A.Ion exchange, in which the membrane trades the molecule for a sodium ion
    • B.Convection, in which solute is dragged across the membrane along with ultrafiltered water✓ Answer
    • C.Osmosis, because the molecule follows water into the dialysate
    • D.Diffusion, because large molecules diffuse faster than small ones

    Diffusion works best for small solutes such as urea and creatinine; the larger the molecule, the more slowly it diffuses. Middle molecules like beta-2 microglobulin are cleared mainly by convection, or solvent drag, in which they are swept across the membrane in the water that is being ultrafiltered. This is why convective therapies are used when middle-molecule removal matters.

    Source: NNCC CCHT content outline — Technical: apply the scientific principles of dialysis underlying patient careReport a problem with this question

13. 13. During treatment, urea moves out of the patient's blood and into the dialysate. What drives that movement?

    • A.A chemical in the dialysate that binds urea and pulls it out of the blood
    • B.A concentration gradient: urea diffuses across the semipermeable membrane from the blood, where it is more concentrated, toward the dialysate, where it is less concentrated✓ Answer
    • C.A pressure gradient created by the blood pump forcing urea through the membrane
    • D.Osmosis, in which urea follows water into the dialysate compartment

    Diffusion is the movement of solute across a semipermeable membrane from an area of higher concentration to an area of lower concentration until equilibrium is approached. Urea, creatinine, and potassium leave the blood this way, while bicarbonate and calcium move the other way when the dialysate concentration is higher. Pressure moves water, not solute, and osmosis describes water movement.

    Source: NNCC CCHT content outline — Technical: apply the scientific principles of dialysis underlying patient careReport a problem with this question

14. 14. A patient must have several liters of retained fluid removed during the treatment. Which physical principle accomplishes that fluid removal?

    • A.Osmosis: the blood pump creates suction that pulls water out of the blood
    • B.Convection: the dialysate chemically absorbs the excess water
    • C.Diffusion: water moves from where it is more concentrated to where it is less concentrated
    • D.Ultrafiltration: water is pushed across the membrane by a pressure difference between the blood and dialysate compartments✓ Answer

    Ultrafiltration is fluid removal driven by a pressure gradient across the membrane, not by a concentration gradient. The pressure difference between the blood compartment and the dialysate compartment is the transmembrane pressure, and it is what pushes plasma water out of the blood so the patient reaches the prescribed post-treatment weight.

    Source: NNCC CCHT content outline — Technical: apply the scientific principles of dialysis underlying patient care (e.g., ultrafiltration)Report a problem with this question

15. 15. Which statement describes osmosis as the term is used in dialysis?

    • A.Solute moves across the membrane from the more concentrated side to the less concentrated side
    • B.Water moves across a semipermeable membrane from the side with the lower solute concentration toward the side with the higher solute concentration✓ Answer
    • C.Water is forced across the membrane by a pressure difference between the two compartments
    • D.Solute is carried across the membrane by the flow of water being pushed through it

    The four transport principles are easy to confuse. Osmosis is water moving toward the higher solute concentration; diffusion is solute moving toward the lower solute concentration; ultrafiltration is water moved by pressure; convection is solute carried along by that moving water. Each of the three wrong options describes one of the other three principles.

    Source: Kallenbach, Review of Hemodialysis for Nurses and Dialysis Personnel — principles of solute and water transportReport a problem with this question

16. 16. A patient has gained fluid weight since the last treatment and also has a high blood urea level. Which pairing correctly identifies the principle responsible for each part of the treatment?

    • A.The fluid weight is removed by convection; the urea is removed by osmosis
    • B.The fluid weight is removed by ultrafiltration; the urea is removed mainly by diffusion✓ Answer
    • C.The fluid weight is removed by diffusion; the urea is removed by ultrafiltration
    • D.Both the fluid and the urea are removed by osmosis

    Hemodialysis does two separate jobs by two separate mechanisms. Fluid comes off by ultrafiltration, driven by the pressure difference across the membrane, while wastes such as urea come off by diffusion, driven by the concentration difference between blood and dialysate. Keeping the two straight explains why a treatment can clear wastes well and still leave a patient volume overloaded if the fluid goal was not met.

    Source: NNCC CCHT content outline — Technical: apply the scientific principles of dialysis underlying patient careReport a problem with this question

17. 17. Inside the dialyzer, blood and dialysate flow in opposite directions. Applying the principle of diffusion, why is that countercurrent arrangement used?

    • A.It prevents blood and dialysate from ever reaching the same temperature
    • B.It slows the blood down so that red cells have time to release potassium
    • C.It keeps a concentration difference between blood and dialysate along the whole length of the fibers, so diffusion continues from one end of the dialyzer to the other✓ Answer
    • D.It lets the dialysate push water back into the blood at the venous end

    Diffusion stops when the two sides reach equilibrium. If blood and dialysate ran in the same direction they would equilibrate partway through the dialyzer and transfer would slow. Running them countercurrent means blood always meets dialysate that is relatively cleaner, so a concentration gradient, and therefore solute removal, is preserved over the entire membrane surface.

    Source: Kallenbach, Review of Hemodialysis for Nurses and Dialysis Personnel — countercurrent flow in the dialyzerReport a problem with this question

18. 18. Comparing urea, a very small molecule, with albumin, a large protein, which statement about their movement across a dialyzer membrane is correct?

    • A.Both cross at the same rate because the membrane is equally permeable to every solute
    • B.Neither crosses, because the membrane allows only water to move
    • C.Albumin crosses more readily because larger molecules carry more energy
    • D.Urea crosses readily because small molecules diffuse rapidly through the membrane pores, while albumin is too large to pass and remains in the blood✓ Answer

    A dialyzer membrane is semipermeable: it is selective by molecular size. Small solutes such as urea and creatinine pass easily and are cleared quickly by diffusion, larger middle molecules pass slowly and depend more on convection, and proteins the size of albumin, along with blood cells, should not cross at all. Loss of albumin across the membrane would be an abnormal finding, not a goal of treatment.

    Source: Core Curriculum for the Dialysis Technician (Medical Education Institute) — dialyzer membranes and solute sizeReport a problem with this question

19. 19. The prescription is changed so that dialysate flows through the dialyzer at a faster rate, with everything else unchanged. What is the expected effect on solute clearance, and why?

    • A.Clearance decreases, because faster dialysate flow raises the solute concentration on the dialysate side
    • B.Clearance increases, because fresh dialysate sweeps away solute that has crossed the membrane and keeps the concentration gradient steep✓ Answer
    • C.Clearance decreases, because the solute has less time to diffuse across the membrane
    • D.Clearance is unchanged, because only the membrane surface area can affect it

    Diffusion depends on the size of the concentration difference across the membrane. Faster dialysate flow continuously replaces solute-laden dialysate with fresh dialysate, keeping the dialysate-side concentration low and the gradient steep, so more solute moves. Blood flow rate, membrane surface area, and permeability push clearance in the same direction; the actual settings are always those in the physician's prescription.

    Source: NNCC CCHT content outline — Technical: apply the scientific principles of dialysis underlying patient careReport a problem with this question

20. 20. The amount of fluid ultrafiltered from a patient during a treatment depends on which combination of factors?

    • A.The urea concentration of the blood and the gauge of the arterial needle
    • B.The number of times the blood passes through the dialyzer and the temperature of the treatment room
    • C.The sodium concentration of the dialysate and the patient's hemoglobin
    • D.The transmembrane pressure applied across the membrane, the ultrafiltration coefficient of the dialyzer, and how long that pressure is applied✓ Answer

    Fluid removal is a pressure phenomenon: the volume ultrafiltered equals the transmembrane pressure multiplied by the dialyzer's ultrafiltration coefficient multiplied by time. The coefficient is a fixed property of the dialyzer describing how much water crosses per unit of pressure, which is why a high-flux dialyzer removes more fluid at the same pressure. Solute concentrations govern diffusion, not ultrafiltration.

    Source: Kallenbach, Review of Hemodialysis for Nurses and Dialysis Personnel — transmembrane pressure and the ultrafiltration coefficientReport a problem with this question

21. 21. A patient's pre-treatment weight is higher than the target (dry) weight recorded in the chart. Why can that difference in kilograms be treated as a nearly equal volume of fluid in liters?

    • A.Because the scale automatically converts body weight into blood volume
    • B.Because the difference reflects new muscle and fat tissue built up between treatments
    • C.Because the weight gained between treatments is almost entirely retained water, and a kilogram of water occupies about a liter of volume✓ Answer
    • D.Because kilograms and liters are simply two names for the same unit of weight

    A patient with little or no urine output stores what he drinks, so interdialytic weight gain is essentially water, and water's density makes one kilogram equal about one liter. That is why the fluid to be removed is calculated from pre-treatment weight minus target weight, with rinseback saline and anything taken by mouth during treatment added in. Body tissue is not built or lost fast enough to explain a gain over two days.

    Source: NNCC CCHT content outline — Clinical: pre-treatment assessment and determination of fluid to be removedReport a problem with this question

22. 22. A preceptor explains that fluid should not be removed faster than the patient's tissues can refill the bloodstream. Which explanation of vascular refill is correct?

    • A.Ultrafiltration takes water out of the blood compartment; if it is removed faster than fluid shifts from the tissues back into the vessels, circulating volume falls and the patient may develop hypotension, cramping, or nausea✓ Answer
    • B.Refill is instantaneous, so the rate of fluid removal cannot produce symptoms
    • C.Ultrafiltration removes water directly from the tissues, so the bloodstream is never affected
    • D.Symptoms occur because removing fluid raises the concentration of urea in the blood

    Ultrafiltration can only pull water from the blood that is inside the extracorporeal circuit's reach, and most of the patient's excess fluid sits in the tissues. Fluid must shift from the interstitial space into the vessels to replace what is taken, and that shift takes time. Removing faster than refill drops the circulating volume and blood pressure, which is why the technician reports hypotension, cramping, or nausea to the nurse and follows facility protocol for the response.

    Source: NNCC CCHT content outline — Clinical: monitor the patient during treatment and report complications; Core Curriculum for the Dialysis Technician (Medical Education Institute)Report a problem with this question

Practice questions based on the NNCC CCHT content outline, CDC recommendations for hemodialysis settings, and the OSHA Bloodborne Pathogens Standard. Not affiliated with or endorsed by NNCC, and not medical advice. Machine settings, dialysate composition, flow rates, alarm thresholds, water-quality limits and laboratory targets are deliberately never the answer to a question here — those are set by your machine's manufacturer, your facility's protocol and the physician's prescription. Always follow your facility's policies and your patient's prescribed treatment. About the CCHT exam (NNCC) →