Patient Assessment and Lab Interpretation
Key Takeaways
- Pre-dialysis assessment includes weight vs dry weight, BP, access inspection, symptom review, and medication reconciliation.
- Critical labs: potassium, phosphorus, calcium (corrected), bicarbonate, hemoglobin, albumin, and dialysis adequacy markers (Kt/V, URR).
- Kt/V ≥1.2 per treatment (or monthly composite) and URR ≥65% are common adequacy targets for thrice-weekly HD.
- nPCR (normalized protein catabolic rate) near 1.0 g/kg/day suggests adequate protein intake; low values prompt nutrition referral.
- Trend analysis beats single values — compare labs, weights, and symptoms across treatments.
Patient Assessment and Lab Interpretation
Quick Answer: Every HD treatment starts with weight vs dry weight, blood pressure, access check, and symptom screen. Interpret K+, phosphorus, calcium, bicarbonate, Hgb, albumin, and Kt/V/URR in trend context — one lab rarely tells the whole story.
CDN exam scenarios embed labs in clinical stories. Your task is to identify the priority abnormality, the nursing action that is complete, and the finding that requires immediate escalation.
Pre-Dialysis Assessment Framework
| Step | What to assess | Why it matters on the exam |
|---|---|---|
| Weight | Pre-weight vs dry weight → IDWG | Fluid prescription and hypertension clues |
| Vital signs | BP, heart rate, temperature | Hypotension risk, infection, hyperkalemia instability |
| Access | Thrill/bruit (fistula/graft), catheter exit site | Clot, infection, stenosis red flags |
| Symptoms | SOB, chest pain, cramping, confusion | Uremia, fluid overload, electrolyte emergency |
| Medications | Held ACE/ARB? Binder adherence? | Explains K+ and phosphorus trends |
| Last dialysis | Missed treatment? Shortened run? | Explains acute lab spikes |
Document findings in the medical record per ESRD Conditions for Coverage expectations — accurate weights drive ultrafiltration orders.
Interdialytic Weight Gain and Dry Weight
IDWG (kg) = pre-dialysis weight − dry weight
IDWG % = IDWG ÷ dry weight × 100
| IDWG % | Risk interpretation |
|---|---|
| <4.8% | Generally acceptable on many units |
| 4.8–5.7% | Caution — fluid overload symptoms more likely |
| >5.7% | High risk for HTN, HF exacerbation, cramping |
Dry weight is adjusted when the patient remains hypertensive despite UF, or hypotensive/cramping when euvolemic. Nurses communicate trends to nephrology — do not change dry weight independently on the exam unless the stem describes a standing protocol.
Key Laboratory Values
| Lab | Typical concern threshold (context-dependent) | Nursing implication |
|---|---|---|
| Potassium | >5.5 mEq/L pre-HD | Diet review, ECG if high, dialysis potassium bath per order |
| Phosphorus | >5.5 mg/dL | Binders, diet, adherence |
| Calcium (corrected) | <8.4 or >10.2 mg/dL | Binder class, vitamin D side effects |
| Bicarbonate | <22 mEq/L | Acidosis, worsens K+ |
| Hemoglobin | Below unit ESA trigger (~10 g/dL) | Fatigue, ESA/iron protocol |
| Albumin | <3.5 g/dL trend low | Nutrition + inflammation workup |
| BUN/Creatinine | Trends | Adequacy and protein intake clues |
Corrected calcium accounts for albumin:
Corrected Ca ≈ measured Ca + 0.8 × (4.0 − albumin)
Exam items may give uncorrected calcium with low albumin — recognize true hypocalcemia may be masked.
Dialysis Adequacy: Kt/V and URR
Adequacy asks whether dialysis removed enough urea. Common thrice-weekly HD targets:
| Metric | Common minimum target |
|---|---|
| spKt/V | ≥1.2 per treatment (or monthly composite equivalent) |
| URR (urea reduction ratio) | ≥65% |
URR = (pre-BUN − post-BUN) ÷ pre-BUN × 100
Low adequacy causes uremic symptoms despite scheduled treatments — check blood flow, dialyzer function, access recirculation, treatment time, and missed sessions.
nPCR (normalized protein catabolic rate) estimates protein intake from urea appearance:
- ~1.0 g/kg/day — adequate protein intake for many HD patients
- <0.8 — malnutrition concern, dietitian referral
Access Assessment Essentials
| Access type | Daily check | Red flag |
|---|---|---|
| AVF | Thrill, bruit, absence of infection | Absent thrill — thrombosis until proven otherwise |
| AVG | Same as fistula | Higher stenosis risk — monitor for arm swelling |
| Tunneled catheter | Exit site, dressing integrity | Purulent drainage, fever — bloodstream infection workup |
Never use AVF/AVG for blood draws or BP on the access arm — exam items test this rule.
Worked Exam Scenario
Pre-HD data: weight 78 kg (dry weight 73 kg), K+ 6.3, phosphorus 5.8, BP 182/96, lungs with basilar crackles, missed last session for hospitalization.
Priority: Hyperkalemia with volume overload after missed dialysis — coordinate extended treatment or urgent management per protocol, cardiac monitoring, and UF prescription adjustment. Teaching diet alone is insufficient.
IDWG: 5 kg ÷ 73 ≈ 6.8% — excessive fluid.
Documentation and Communication
CDN items may test interdisciplinary communication:
- Report critical labs to nephrology per facility policy
- Notify physician for access failure, chest pain, neurologic change
- Educate patients on home BP, fluid limits, binder timing
Common CDN Traps
- Using post-dialysis potassium to judge pre-dialysis danger in the same stem
- Ignoring missed treatments as root cause
- Forgetting albumin correction for calcium
- Selecting access arm BP as acceptable practice
Study Routine
- Calculate URR and IDWG % from three practice stems
- Build a pre-HD assessment checklist card
- Match lab pairs to likely nursing action (K+ 6.4 → monitor ECG, not just diet handout)
Final Check
List six pre-HD assessment steps, state Kt/V and URR targets, and compute IDWG percent for dry weight 70 kg and pre-weight 74.5 kg.
Intradialytic and Post-Dialysis Monitoring
During HD, monitor hypotension, cramping, chest pain, and access alarms. Post-weight should approach dry weight per prescription. Disequilibrium syndrome — headache, nausea, neurologic change after rapid urea clearance in new starts — requires slowing or stopping dialysis per protocol.
Patients with residual urine output clear potassium and fluid more effectively until GFR falls further; document urine trends. Catheter patients with fever need blood culture protocols; connect infection risk to access type in scenario analysis.
A thrice-weekly hemodialysis patient has pre-BUN 64 mg/dL and post-BUN 19 mg/dL. What is the urea reduction ratio (URR)?
Before connecting a patient with an arteriovenous fistula in the left forearm, which action violates standard access protection?
A patient's dry weight is 70 kg and today's pre-dialysis weight is 74.2 kg. Interdialytic weight gain is 4.2 kg. What is the IDWG percentage and clinical implication?