Free NCLEX lab values practice questions
Four free NCLEX-RN lab interpretation questions covering digoxin + hypokalemia, ABG decoding, vancomycin trough monitoring, and pre-vancomycin labs. Lab questions are rarely "what is the normal range?" — they're almost always "what should you do about this abnormal result?"
Lab value applications that win NCLEX points
- Potassium + digoxin. K+ < 3.5 = digoxin toxicity risk.
- Insulin + potassium. Insulin drives K+ intracellularly. Expect K+ to drop during DKA treatment.
- Heparin + aPTT. Therapeutic 60–80 sec. > 100 = hold, notify, consider protamine.
- Warfarin + INR. Therapeutic 2–3 (3–4 for mechanical valve). > 5 = hold + vitamin K.
- Vancomycin trough. 10–20 mcg/mL. > 20 = nephrotoxicity, ototoxicity risk.
- Lithium. Narrow window 0.6–1.2 mEq/L. > 1.5 toxic. Watch for dehydration and NSAIDs.
- BNP. > 400 heart failure. Trend to assess volume status.
- Troponin. Any elevation suggests myocardial injury. Rises 3–4 hr post-MI.
- Lactate. > 2 in sepsis suggests tissue hypoperfusion. > 4 indicates septic shock until proven otherwise.
ABG decoding flow
- pH first. Below 7.35 acidosis. Above 7.45 alkalosis.
- PaCO2. Moves opposite to pH = respiratory cause.
- HCO3. Moves with pH = metabolic cause.
- If both abnormal: compensation. Fully normal pH = fully compensated.
- PaO2 < 60 = respiratory failure regardless of pH.
Critical values to memorize cold
- K+ < 2.5 or > 6.5
- Na+ < 120 or > 160
- Glucose < 40 or > 500
- Ca++ < 7 or > 13
- Platelets < 50,000
- Hgb < 7
- pH < 7.20 or > 7.60
- PaO2 < 60
- INR > 5 (especially with bleeding)
For a complete reference, see our NCLEX lab values cheat sheet.
Try these 4 questions now
No signup required. Tap an answer to reveal the rationale.
- Question 1 · Lab interpretation · MCQ
A client receiving digoxin has a serum potassium of 2.9 mEq/L. Which is the priority intervention?
- a.Continue the digoxin and document the K+
- b.Hold the next digoxin dose and notify the provider for K+ replacement
- c.Increase the digoxin dose to compensate
- d.Encourage potassium-rich foods at the next meal
Show answer + rationale
Correct: B. Hypokalemia (K+ <3.5) significantly increases digoxin toxicity risk. With K+ at 2.9, hold the dig and replace potassium IV or PO depending on severity. Foods alone won't correct this fast enough.
- Question 2 · Lab interpretation · MCQ
Which ABG result indicates uncompensated metabolic acidosis?
- a.pH 7.32, PaCO2 38, HCO3 18
- b.pH 7.46, PaCO2 28, HCO3 22
- c.pH 7.30, PaCO2 50, HCO3 24
- d.pH 7.36, PaCO2 30, HCO3 18
Show answer + rationale
Correct: A. Uncompensated metabolic acidosis: low pH (<7.35), low HCO3 (<22), normal PaCO2 (35–45). Option B is respiratory alkalosis. Option C is respiratory acidosis. Option D shows compensated metabolic acidosis (pH normalized, PaCO2 dropped to compensate).
- Question 3 · Lab interpretation · MCQ
A client receiving vancomycin has a trough of 24 mcg/mL. Which action is most appropriate?
- a.Continue the same dose
- b.Hold the next dose and notify the provider
- c.Increase the dose to maintain therapy
- d.Switch to oral vancomycin
Show answer + rationale
Correct: B. Therapeutic vancomycin trough is 10–20 mcg/mL. A trough of 24 is supratherapeutic and increases nephrotoxicity and ototoxicity risk. Hold the dose, notify the provider, and check renal function. Oral vancomycin is used for C. diff colitis, not systemic infection.
- Question 4 · Pharmacology · MCQ
Which laboratory value must the nurse verify before administering IV vancomycin?
- a.Liver function tests
- b.Serum creatinine and trough level
- c.Hemoglobin and hematocrit
- d.Prothrombin time
Show answer + rationale
Correct: B. Vancomycin is nephrotoxic and dose adjustments depend on renal function. Trough levels (drawn 30 min before the next dose) guide dosing to keep levels therapeutic (typically 10–20 mcg/mL) without toxicity. LFTs, CBC, and PT are not the primary monitoring labs for vancomycin.
These are 5 of 5,000+ NCLEX questions in the Clarity bank. The full bank includes real NGN case studies, bow-tie items, AI tutor follow-up, and 5 readiness exams.
Get 5,000+ more questions free for 10/day →Frequently asked questions
What lab values do I need to memorize for NCLEX?
Top 20: Na, K, Ca, Mg, glucose, BUN, creatinine, hemoglobin, hematocrit, platelets, WBC, INR, aPTT, pH, PaCO2, HCO3, PaO2, troponin, BNP, plus therapeutic levels for digoxin, lithium, phenytoin, and vancomycin.
How do I interpret ABG quickly?
pH first. PaCO2 second (respiratory cause if moves opposite to pH). HCO3 third (metabolic cause if moves with pH). Both abnormal = compensation occurring.
What's the priority when potassium is 6.5?
Hyperkalemia critical. Continuous EKG monitoring (peaked T waves, prolonged QRS, dysrhythmias), calcium gluconate to stabilize myocardium, insulin + dextrose or kayexalate to shift/eliminate K+. Hold ACE inhibitors, K-sparing diuretics, and potassium-containing fluids.
When is INR too high?
Therapeutic INR on warfarin is 2.0–3.0 (2.5–3.5 for mechanical valves). INR above 5 carries significant bleeding risk and typically warrants holding warfarin and possibly giving vitamin K. INR above 10 requires reversal with vitamin K or PCC.