CDN common mistakes
CDN · Understand the traps and how to avoid them.
Staging chronic kidney disease by the serum creatinine value alone instead of using eGFR and albuminuria categories.
Creatinine varies with muscle mass, age, and sex, so a normal-looking creatinine can mask significant kidney function loss; exam items often present eGFR and expect KDIGO staging.
What to do instead
Practice mapping eGFR ranges to stages G1 through G5, including 3a and 3b, and pair staging with albuminuria categories A1 through A3 before answering.
Choosing a calcium-based phosphate binder for a patient with hyperphosphatemia and a high serum calcium level.
Candidates focus only on the phosphate value and forget that calcium-based binders can worsen hypercalcemia and vascular calcification in chronic kidney disease–mineral and bone disorder.
What to do instead
Review calcium, phosphate, PTH, and vitamin D together; select a non-calcium binder when calcium is high, and answer based on the full mineral panel rather than one lab value.
Calculating urea reduction ratio or Kt/V with the wrong numerator or denominator, or applying peritoneal dialysis adequacy targets to hemodialysis.
The formulas look similar, and candidates confuse pre-dialysis and post-dialysis BUN placement or mix hemodialysis and peritoneal dialysis thresholds.
What to do instead
Use URR = (pre-BUN minus post-BUN) divided by pre-BUN times 100; remember hemodialysis targets of URR at least 65% and Kt/V at least 1.2 per treatment, while peritoneal dialysis uses a weekly Kt/V target of at least 1.7.
Continuing hemodialysis after a needle infiltration or flushing the infiltrated site to try to salvage the treatment.
Candidates want to avoid interrupting the prescription and underestimate the risk of hematoma, nerve compression, and access loss.
What to do instead
Stop the blood pump, remove the needle, apply direct pressure, use ice initially, cannulate a different site if treatment must continue, document the event, and reassess the access.
Treating cloudy peritoneal effluent as an exit-site infection or delaying antibiotic therapy until the culture result returns.
Candidates confuse the definitions of peritonitis and exit-site infection and worry about giving antibiotics before cultures.
What to do instead
Recognize peritonitis as cloudy effluent with abdominal pain and effluent white blood cell count greater than 100/microliter with more than 50% neutrophils; send effluent for cell count and culture, then start empiric intraperitoneal antibiotics promptly.
Interpreting a peritoneal equilibration test without accounting for dextrose concentration and dwell time, or misclassifying a high transporter as having good ultrafiltration.
Candidates memorize transporter labels but forget that high transporters absorb glucose rapidly, leading to poor ultrafiltration with long dwells.
What to do instead
Use the standardized peritoneal equilibration test with 2.27% dextrose and a 4-hour dwell; for high transporters, shorten dwell times or use icodextrin rather than assuming ultrafiltration is adequate.
Giving a fluid bolus for post-hemodialysis headache, confusion, or seizures without considering dialysis disequilibrium syndrome.
These symptoms overlap with hypotension, and candidates default to the most familiar complication rather than the timing and neurologic pattern.
What to do instead
Differentiate dialysis disequilibrium syndrome by its neurologic symptoms and recent initiation or rapid BUN reduction; prevent it with slower blood flow, shorter first sessions, and gradual solute removal, and treat it as a neurologic emergency rather than simple hypotension.
Waiting for a serum potassium result before treating a patient with peaked T waves or a widened QRS complex.
Candidates rely on the laboratory value and forget that ECG changes indicate emergency hyperkalemia requiring immediate treatment.
What to do instead
Treat ECG changes immediately with intravenous calcium for cardiac stabilization, followed by insulin with glucose, a beta-agonist, and urgent dialysis; do not delay for the potassium result.
Documenting patient education after asking only “Do you understand?” instead of having the patient demonstrate or explain the skill.
Candidates equate verbal confirmation with learning and do not assess health literacy, language, or sensory barriers.
What to do instead
Use teach-back: ask the patient to explain the fluid limit, medication timing, or cannulation care in their own words or demonstrate it; re-teach and use an interpreter or low-literacy materials when needed.
Labeling missed dialysis treatments as noncompliance without screening for depression, transportation problems, financial barriers, or cognitive impairment.
Candidates jump to a behavioral explanation and miss modifiable psychosocial and practical barriers that the exam expects to be assessed.
What to do instead
Screen for depression and social determinants, ask directly about transportation, cost, caregiving, and scheduling, and refer to social work, behavioral health, or financial counseling before documenting nonadherence.