22 Renal Physiology & Dialysis Principles Practice Questions & Answers

1. 1. A new technician is learning the parts of the nephron. Which structure is the site where blood is first filtered to form the fluid that later becomes urine?

   • A.The proximal tubule, where most of the filtered water and useful solutes are taken back
   • B.The collecting duct, where the final adjustment of water content is made before voiding
   • C.The renal pelvis, which gathers the finished urine and channels it into the ureter
   • D.The glomerulus, a tuft of capillaries where water and small solutes leave the blood✓ Answer

   Filtration takes place only at the glomerulus, where pressure in the capillary tuft forces water and small solutes into Bowman's capsule. The tubule and collecting duct then reabsorb and secrete to refine that filtrate, and the renal pelvis merely collects urine that is already finished.

   Source: Core Curriculum for the Dialysis Technician, renal anatomy and physiology (structure of the nephron)Report a problem with this question

2. 2. About 180 liters of fluid are filtered by the kidneys each day, yet a healthy adult passes only one to two liters of urine. Which process explains that difference?

   • A.Nearly all of the filtered fluid is reabsorbed from the tubules back into the bloodstream✓ Answer
   • B.Most of the filtered fluid is broken down by the kidney cells and never has to leave
   • C.The glomerulus filters only in short bursts, so for most of the day no filtrate is made at all
   • D.The bladder absorbs the greater part of the fluid back through its wall before urination

   Roughly ninety-nine percent of the glomerular filtrate is reabsorbed by the tubules and returned to the blood, which is why an enormous filtered volume ends up as a small volume of urine. Filtration is continuous, the kidney does not destroy fluid, and the bladder only stores urine.

   Source: Core Curriculum for the Dialysis Technician, glomerular filtration and tubular reabsorptionReport a problem with this question

3. 3. A patient asks how healthy kidneys can make urine that is far more concentrated than blood. The technician's answer should be based on which function of the loop of Henle?

   • A.It builds a salty gradient in the tissue around it, and that gradient pulls water out of the tubule fluid✓ Answer
   • B.It filters plasma proteins out of the blood, so the fluid leaving it is already concentrated
   • C.It adds bicarbonate to the tubule fluid, and that added buffer is what raises concentration
   • D.It secretes extra urea straight into the bladder, so the stored urine slowly becomes thicker

   The loop of Henle concentrates sodium and urea in the tissue of the renal medulla. Because that tissue is saltier than the fluid inside the collecting duct, water is drawn osmotically out of the duct and concentrated urine is produced.

   Source: Core Curriculum for the Dialysis Technician, urine concentration and the countercurrent mechanismReport a problem with this question

4. 4. A patient on maintenance hemodialysis asks why he still needs injections for his low blood count when he comes for dialysis three times a week. The technician's response should be based on the understanding that:

   • A.iron builds up during each dialysis, and the injections are given to pull that excess out of the marrow
   • B.the failed kidneys no longer make enough erythropoietin, and dialysis does not replace that hormone✓ Answer
   • C.the injections thin the blood so that it flows through the dialyzer without clotting on the way
   • D.dialysis removes red blood cells along with the wastes, so the injections replace what was lost

   Erythropoietin is made by healthy kidneys and signals the bone marrow to produce red blood cells. Hemodialysis replaces the filtering work of the kidney but not its hormone production, so the anemia of kidney failure is treated with a drug that stimulates the marrow rather than with more dialysis.

   Source: KDIGO Clinical Practice Guideline for Anemia in Chronic Kidney Disease; Core Curriculum for the Dialysis Technician, endocrine functions of the kidneyReport a problem with this question

5. 5. In kidney failure the kidneys can no longer activate vitamin D. Which chain of events follows from that single loss?

   • A.Bicarbonate is lost in the stool, the blood turns alkaline, and the parathyroid glands slow their release
   • B.Less calcium is absorbed from food, serum calcium falls, and the parathyroid glands release more hormone✓ Answer
   • C.More calcium is absorbed from food, serum calcium rises above normal, and the parathyroid glands shut down
   • D.Potassium absorption from the diet climbs sharply, and the parathyroid glands release hormone to correct it

   The kidney performs the final step that turns vitamin D into its active form, and only the active form lets the intestine absorb calcium. When it is missing, serum calcium falls and phosphorus rises, the parathyroid glands are driven into secondary hyperparathyroidism, and the extra hormone pulls calcium out of bone.

   Source: KDIGO Clinical Practice Guideline for Chronic Kidney Disease-Mineral and Bone Disorder; Core Curriculum for the Dialysis Technician, mineral metabolismReport a problem with this question

6. 6. A patient asks the technician, “Why did the doctor start me on a special vitamin D?” The technician's answer should be based on the understanding that active vitamin D is needed to:

   • A.raise the red blood cell count and relieve the feeling of tiredness
   • B.lower blood pressure by getting rid of extra body fluid
   • C.keep calcium in balance so that the bones stay strong✓ Answer
   • D.help the body clear extra potassium between treatments

   Active vitamin D allows the intestine to absorb calcium and keeps calcium and phosphorus in balance, which is what protects bone; failing kidneys can no longer carry out that activation. Anemia is treated with an agent that stimulates red cell production, and vitamin D is not a potassium or blood-pressure treatment.

   Source: Core Curriculum for the Dialysis Technician, vitamin D activation and bone healthReport a problem with this question

7. 7. A patient with kidney failure has high blood pressure at nearly every treatment. Which explanation of the mechanism is correct?

   • A.Damaged kidneys make too much erythropoietin, and the thickened blood raises blood pressure
   • B.Damaged kidneys destroy bicarbonate, and the acid that builds up raises the blood pressure
   • C.Damaged kidneys retain sodium and water and also release renin, and both of these raise blood pressure✓ Answer
   • D.Damaged kidneys pour out sodium and water too fast, and the dryness raises blood pressure

   Two mechanisms act at the same time: the failing kidney cannot excrete its sodium and water load, so circulating volume expands, and it also releases renin, which activates angiotensin and aldosterone and constricts blood vessels. That is why both fluid control and medication are used.

   Source: Core Curriculum for the Dialysis Technician, renin-angiotensin-aldosterone system and hypertension in kidney failureReport a problem with this question

8. 8. Kidney failure leaves the blood too acidic. During hemodialysis, how is that acid-base problem corrected?

   • A.Warming the dialysate breaks the acid down into gases that the patient then breathes out
   • B.The pressure gradient across the membrane squeezes the acid out along with the fluid removed
   • C.The dialyzer membrane chemically neutralises the acid as the blood passes along the fibers
   • D.Buffer moves from the dialysate into the blood while acids move out into the dialysate✓ Answer

   The buffer in the dialysate is more concentrated than the buffer in the patient's blood, so it diffuses into the blood while acid anions diffuse the other way. Diffusion down a concentration gradient, not pressure or heat, corrects the metabolic acidosis of kidney failure.

   Source: Core Curriculum for the Dialysis Technician, acid-base balance and buffer transfer during hemodialysisReport a problem with this question

9. 9. A patient who has missed two treatments tells the technician that he has no appetite, that food tastes like metal, and that he itches all over. These complaints are most consistent with:

   • A.a reaction to the dialyzer membrane that first began at his last completed treatment
   • B.a build-up of waste products in the blood that the kidneys can no longer remove✓ Answer
   • C.the loss of too much fluid at his last visit, leaving him below his dry weight
   • D.a drop in blood sugar caused by the long gap between the missed treatments

   Loss of appetite, a metallic taste, and generalized itching are classic uremic symptoms produced by retained nitrogenous wastes, and missed treatments let those wastes accumulate. They point to underdialysis rather than to a membrane reaction or a blood sugar problem, and should be reported.

   Source: Core Curriculum for the Dialysis Technician, uremia and the signs and symptoms of inadequate dialysisReport a problem with this question

10. 10. On a Monday morning a patient reports that since Friday his heart has felt like it is skipping and his legs have become weak and heavy. Which action should the technician take first?

    • A.Tell the nurse what the patient has described before the treatment is begun✓ Answer
    • B.Begin the treatment as scheduled and mention the complaints at the end of it
    • C.Offer the patient a snack, since weakness usually means the blood sugar is low
    • D.Have the patient walk to the scale again to see whether the weakness passes

    Palpitations together with new muscle weakness after a long interdialytic interval suggest a dangerously high potassium level, which can stop the heart. Interpreting those symptoms and changing the plan of care is outside the technician's role, so the report must reach the nurse before treatment starts.

    Source: CMS ESRD Conditions for Coverage, 42 CFR 494.80, patient assessment; Core Curriculum for the Dialysis Technician, potassium and the predialysis patient interviewReport a problem with this question

11. 11. Which pairing correctly describes what happens in the blood of a patient with end-stage kidney disease?

    • A.Only fluid is retained; the dissolved wastes and salts stay within their normal range
    • B.Bicarbonate and calcium build up, while urea, creatinine and potassium fall below normal
    • C.Urea, creatinine, potassium and phosphorus build up, while bicarbonate and calcium run low✓ Answer
    • D.Every substance measured in the blood rises together, because nothing is being excreted

    Substances the kidney normally excretes accumulate, so urea, creatinine, potassium and phosphorus rise. Substances the kidney normally makes or conserves become deficient, so bicarbonate falls and metabolic acidosis develops, and calcium falls because vitamin D is no longer activated.

    Source: Core Curriculum for the Dialysis Technician, laboratory changes in end-stage kidney diseaseReport a problem with this question

12. 12. A patient who has been on hemodialysis for many years develops carpal tunnel syndrome and shoulder pain. This long-term complication is linked to the build-up of:

    • A.urea, the small waste molecule that the dialyzer removes least efficiently
    • B.albumin, the large protein that crosses the membrane easily during treatment
    • C.beta-2 microglobulin, a middle-sized protein that dialysis clears only poorly✓ Answer
    • D.excess bicarbonate that the dialysate adds back to the blood at every treatment

    Beta-2 microglobulin is a middle molecule that diffuses poorly across dialysis membranes, so it accumulates over years and deposits as amyloid in joints, tendons and bone. Those deposits produce carpal tunnel syndrome and shoulder pain; albumin is too large to be lost and urea is the solute cleared best.

    Source: Core Curriculum for the Dialysis Technician, middle molecules and dialysis-related amyloidosisReport a problem with this question

13. 13. During hemodialysis, urea moves from the patient's blood into the dialysate. What drives that movement?

    • A.The difference in temperature between the warmed dialysate and the returning blood
    • B.The difference in urea concentration between the blood side and the dialysate side✓ Answer
    • C.The difference in hydrostatic pressure between the blood side and the dialysate side
    • D.The suction created by the blood pump as it pushes blood through the hollow fibers

    Urea crosses the membrane by diffusion, which is driven by the concentration difference between the two sides. Fresh dialysate contains no urea, so the gradient stays steep and urea keeps moving out of the blood; pressure differences move water rather than solute.

    Source: Core Curriculum for the Dialysis Technician, principles of dialysis (diffusion)Report a problem with this question

14. 14. Blood and dialysate are run through the dialyzer in opposite directions. What is the reason for this design?

    • A.Blood cells are pushed toward the center of each fiber, which helps prevent clotting
    • B.A concentration difference is kept along the whole length of the fiber, so diffusion continues✓ Answer
    • C.The opposing flows cancel each other's pressure, so no fluid is removed by mistake
    • D.Running them in opposite directions warms the blood evenly from one end to the other

    With countercurrent flow the blood always meets dialysate that is less saturated with waste, so a concentration difference exists at every point along the fiber. If the two streams flowed the same way they would approach equilibrium partway along the dialyzer and clearance would fall.

    Source: Core Curriculum for the Dialysis Technician, countercurrent flow and maintenance of the concentration gradientReport a problem with this question

15. 15. A treatment must remove two kilograms of fluid from a patient. Which mechanism actually removes that fluid?

    • A.Osmosis, in which the strong dialysate draws the water across the membrane on its own
    • B.Ultrafiltration, in which a pressure difference across the membrane pushes plasma water out✓ Answer
    • C.Convection, in which the dialysate flow washes water off the outside of the membrane
    • D.Diffusion, in which the concentration gradient pulls the excess water across into the dialysate

    Fluid weight is removed by ultrafiltration, in which a hydrostatic pressure difference across the membrane, expressed as transmembrane pressure, forces plasma water out of the blood. Diffusion moves solute rather than water, so attributing fluid removal to it is the classic error.

    Source: Core Curriculum for the Dialysis Technician, ultrafiltration and transmembrane pressureReport a problem with this question

16. 16. In dialysis teaching, the term osmosis refers to:

    • A.solute moving across a membrane toward the side that has fewer dissolved particles
    • B.solute being dragged across a membrane by the water that is being removed
    • C.water moving across a membrane toward the side with more dissolved particles✓ Answer
    • D.water being pushed across a membrane by a difference in hydrostatic pressure

    Osmosis is the movement of water across a semipermeable membrane from the more dilute side toward the more concentrated side. It explains fluid shifts between body compartments and vascular refill, whereas pressure-driven water movement is ultrafiltration and solvent drag is convection.

    Source: Core Curriculum for the Dialysis Technician, principles of dialysis (osmosis and fluid shifts)Report a problem with this question

17. 17. As plasma water is ultrafiltered across the dialyzer membrane, dissolved solutes are carried along with it. What is this transport called?

    • A.Diffusion, also described as active transport
    • B.Adsorption, also described as surface binding
    • C.Osmosis, also described as passive filtration
    • D.Convection, also described as solvent drag✓ Answer

    Convection, or solvent drag, occurs when solutes dissolved in plasma water are swept across the membrane with the water being ultrafiltered. Because it rides along with fluid removal it is the main route for middle molecules, which diffuse poorly.

    Source: Core Curriculum for the Dialysis Technician, convective transport and solvent dragReport a problem with this question

18. 18. Why does urea pass out of the blood through the dialyzer membrane while albumin stays behind?

    • A.Urea is pumped through the membrane by the machine, and albumin is not pumped at all
    • B.Urea dissolves in the membrane material itself, while albumin cannot dissolve in it
    • C.Urea carries an electrical charge that the membrane attracts, and albumin does not
    • D.Urea fits through the pores of the membrane and albumin is too large to pass✓ Answer

    The dialyzer membrane is semipermeable: its pores are sized to let water and small solutes such as urea pass while holding back blood cells and large proteins such as albumin. Separation depends on molecular size relative to pore size, not on charge, dissolving, or pumping.

    Source: Core Curriculum for the Dialysis Technician, semipermeable membrane characteristics and pore sizeReport a problem with this question

19. 19. The physician wants a patient's urea clearance improved. Which change would be expected to increase clearance?

    • A.Running the dialysate in the same direction as the blood, so the two travel together
    • B.Lowering the blood flow rate, so that the blood spends more time inside the fibers
    • C.Shortening the treatment, so that the concentration gradient stays steep throughout
    • D.Using a dialyzer with a larger membrane surface area, so more area is available for exchange✓ Answer

    Clearance rises when more blood is presented to more membrane for longer, so a larger surface area, a higher blood flow rate, or a longer treatment all increase it. Slowing the blood flow, shortening the treatment, or switching to same-direction flow all reduce clearance instead.

    Source: Core Curriculum for the Dialysis Technician, factors affecting solute clearanceReport a problem with this question

20. 20. A patient's recorded post-dialysis weight at the last treatment was 70.0 kg, and today's pre-dialysis weight is 72.5 kg. No other fluid is to be added or subtracted. What volume should be entered as the ultrafiltration goal?

    • A.2,500 mL, because each kilogram of weight gain is counted as one liter of fluid✓ Answer
    • B.70,000 mL, because the goal is set from the dry weight recorded at the last treatment
    • C.725 mL, because the goal is read directly from the pre-dialysis weight on the scale
    • D.250 mL, because each kilogram of weight gain is counted as one hundred milliliters of fluid

    Body fluid weight is converted one to one, so one kilogram of gain equals one liter, or 1,000 mL. The gain here is 72.5 kg minus 70.0 kg, which is 2.5 kg and therefore 2,500 mL, to which only the volumes named in the prescription would be added.

    Source: Core Curriculum for the Dialysis Technician, calculating interdialytic weight gain and the ultrafiltration goalReport a problem with this question

21. 21. Most of a patient's excess fluid sits in the tissues rather than in the bloodstream. Why must fluid not be removed faster than the tissues can refill the bloodstream?

    • A.The circulating blood volume falls faster than the tissues can replace it, and blood pressure drops✓ Answer
    • B.The wastes would be left behind in the tissues and could never reach the dialyzer at all
    • C.The dialyzer membrane would clog, because the fluid held in the tissues is thicker than plasma
    • D.The tissues would swell painfully as extra fluid is forced back into them from the vessels

    Ultrafiltration takes water out of the blood compartment only, and plasma volume is restored as fluid moves in from the interstitium by vascular refill. When removal outruns refill, circulating volume falls, and the patient becomes hypotensive and may cramp.

    Source: Core Curriculum for the Dialysis Technician, vascular refill and the ultrafiltration rateReport a problem with this question

22. 22. A patient asks the technician to explain what mineral and bone disorder is and why his phosphorus level matters. The technician is not sure of the correct explanation. What is the best response?

    • A.Give the patient the best explanation the technician can put together
    • B.Tell the patient that this is not something the staff members are able to discuss
    • C.Suggest the patient look the answer up online before the next treatment
    • D.Tell the patient that the nurse will come and go over the question with him✓ Answer

    Reinforcing teaching that has already been given is part of the technician's role, but originating an explanation the technician is unsure of is not, and a wrong answer can mislead the patient about diet and medication. Passing the question to the nurse keeps the patient correctly informed and stays within scope.

    Source: CMS ESRD Conditions for Coverage, 42 CFR 494.140, personnel qualifications for patient care dialysis techniciansReport 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) →