NCLEX Diagnostics & Lab Interpretation questions
The PrepScore bank has 88 Diagnostics & Lab Interpretation questions, each with a rationale and two tags: the Client Needs category from the test plan and the clinical judgment step it tests. In this topic the items lean on Take action and Analyze cues, which is worth knowing before you practise it. Three worked samples are below, answers behind a reveal.
ABG analysis, ECG patterns, electrolyte panels, hepatic + cardiac biomarkers, pre-procedure teaching, specimen collection.
Three worked questions
Q1. A medical-surgical nurse receives morning labs on her 4 patients. She has 15 minutes before morning medication pass to identify any critical values requiring provider notification. Which lab value is the PRIORITY for immediate provider notification?
- A. Serum potassium 6.8 mEq/L in a 72-year-old male with new ECG showing peaked T waves and widening QRS
- B. Hemoglobin 12.5 g/dL in a 45-year-old female on routine post-op day 2 from cholecystectomy, asymptomatic
- C. BUN 18 mg/dL in a 60-year-old male on stable management, hemodynamically stable, no acute change
- D. WBC 9.0 K/uL in a 50-year-old female with no symptoms, no fever, routine inpatient follow-up assessment
Show answer and rationale
Answer: Serum potassium 6.8 mEq/L in a 72-year-old male with new ECG showing peaked T waves and widening QRS
Severe hyperkalemia (K 6.8) with ECG changes (peaked T waves + widening QRS) is a medical emergency requiring immediate provider notification and treatment (calcium gluconate + insulin/D50 + albuterol + hemodialysis if needed). Normal hemoglobin, normal BUN, and normal WBC are not priorities.
Q2. A 65-year-old female is admitted to the medical floor with possible sepsis. Vitals: T 39.1°C, HR 118, RR 24, SpO2 94%. The hospital lab nurse is reviewing the CBC differential for signs of bacterial infection. Which findings SUPPORT a bacterial infection? Select all that apply.
- A. WBC > 12 K/uL with neutrophil predominance
- B. Bandemia (left shift, bands > 10% reflecting immature neutrophils)
- C. Toxic granulation noted on the peripheral smear
- D. Lymphocyte predominance with relative neutropenia (viral pattern)
- E. Eosinophilia > 500 cells/uL
- F. Normal CBC with no abnormalities and normal differential
Show answer and rationale
Answer: WBC > 12 K/uL with neutrophil predominanceBandemia (left shift, bands > 10% reflecting immature neutrophils)Toxic granulation noted on the peripheral smear
Bacterial infection CBC pattern: elevated WBC with neutrophil predominance + bandemia (left shift) + toxic granulation on smear. Lymphocyte predominance is the VIRAL pattern; eosinophilia suggests allergy/parasitic; normal CBC excludes by definition.
Q3. A 58-year-old male is receiving IV vancomycin q12h for MRSA bacteremia in the medical ICU. The pharmacy requests a vancomycin trough level before his next dose at 0600. The nurse needs to determine the correct timing for the trough draw. When should the vancomycin trough be drawn?
- A. 30 minutes before the next scheduled dose (true trough — lowest serum concentration before the next infusion)
- B. Immediately after the infusion is complete to measure the peak serum concentration
- C. Mid-infusion to measure the average steady-state serum concentration during therapy
- D. At any time during the dosing interval since trough levels are not time-sensitive at all
Show answer and rationale
Answer: 30 minutes before the next scheduled dose (true trough — lowest serum concentration before the next infusion)
Vancomycin trough is drawn 30 minutes before the next dose — this captures the lowest serum concentration just before the next infusion begins. Post-infusion captures the peak (not trough); mid-infusion captures neither; any-time random draws produce unreliable values.
The rules that decide these questions
From the pack's rule cards — the reasoning shortcuts a wrong answer usually means you were missing.
Read pH (< 7.35 acidosis, > 7.45 alkalosis), then CO2 and HCO3. ROME: Respiratory Opposite (pH and CO2 move opposite directions = respiratory), Metabolic Equal (pH and HCO3 move same direction = metabolic). Anion-gap metabolic acidosis = MUDPILES (methanol, uremia, DKA, propylene glycol, infection/iron/INH, lactic, ethylene glycol, salicylates). Treat the cause, not just the number.
HyperNa + polyuria post-pituitary = DI (DDAVP). HypoNa + cancer + euvolemic = SIADH (fluid restrict, slow correction). HypoK + hypoMg + loop diuretic = waste (replace BOTH — K won't normalize without Mg). HyperK + ACE-I + K-sparing = drug-induced (stabilize → shift → excrete: Ca gluconate → insulin/D50 → Kayexalate/Lokelma/dialysis). Always correct Na ≤ 8-10 mEq/L per 24 h to avoid demyelination.
UNSYNCHRONIZED defibrillation = V-fib + pulseless V-tach. SYNCHRONIZED cardioversion = unstable tachyarrhythmias WITH pulse (unstable VT, unstable A-fib with hemodynamic compromise). Stable A-fib = rate control + anticoagulation, NOT shock. Complete heart block = pacing (atropine often ineffective).
Hepatocellular (ALT > AST, both very high) = direct injury (viral, drug, ischemia). Alcoholic (AST > ALT 2:1, GGT high) = alcohol. Cholestatic (alk phos + GGT very high, direct bili up) = obstruction. INR elevation = synthetic dysfunction. Acetaminophen toxicity: NAC even at day 3 may help; consider transplant evaluation if severe.
Troponin elevation begins 3-6 h post-event, peaks 12-24 h. A single early negative troponin does NOT rule out MI. Serial troponins (q3-6h) needed. BNP elevation correlates with HF severity but is context-dependent (lower in obesity, higher in renal impairment). Never discharge based on a single early troponin.
Warfarin elective surgery: hold 5 d + bridge LMWH per surgeon. Metformin + contrast: hold day of + 48 h after (lactic acidosis risk if AKI). Chronic steroids: CONTINUE + stress-dose at induction (50-100 mg hydrocortisone). DOAC urgent surgery: andexanet alfa (apixaban/rivaroxaban) or idarucizumab (dabigatran) or 4-factor PCC. NPO timing: 8 h full / 6 h light / 4 h breast milk / 2 h clear liquids.
Practise the whole pack, tagged and explained
Every item carries its Client Needs category and clinical judgment step, so a wrong answer names the step that failed.
Frequently asked questions
How many Diagnostics & Lab Interpretation questions does the bank have?
88 multiple-choice items, plus 10 unfolding cases in the Diagnostics & Lab Interpretation pack, each with a rationale.
Are the samples real bank items?
Yes — the three questions above are drawn from the live bank, with their real rationales and tags.
Which clinical judgment steps does this topic train?
Most items in this topic test Take action and Analyze cues, though every step appears.
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