Which lab values do I actually have to memorize for the NCLEX?

Electrolytes, arterial blood gases, a complete blood count, coagulation studies (INR and aPTT), renal function (BUN and creatinine), glucose and A1C, and the classic therapeutic drug levels — digoxin, lithium, phenytoin and vancomycin. Those cover the overwhelming majority of lab-based items.

Do I need the exact number, or just high versus low?

Both, but the exam rewards the action more than the number. Most lab questions ask which patient to see first or what to do next, so pair every range with one recognizable sign and one first nursing action.

How do I read arterial blood gases quickly?

Check the pH first — acidotic or alkalotic. Then check CO2: if it moves opposite the pH, the cause is respiratory; if bicarbonate moves in the same direction as the pH, the cause is metabolic. That is the ROME rule.

What is the fastest way to memorize lab values?

Attach them to a patient instead of a chart. Our story characters carry the numbers with the signs and interventions already connected, which survives test-day pressure much better than a bare list.

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NCLEX Lab Values You Have to Know

Every high-yield normal range, what a high and low result means clinically, and the first nursing action the exam expects — grouped the way lab questions are actually written.

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Reference

Electrolytes

The single most tested lab group on the NCLEX. Know the number, the ECG change, and the first nursing action.

Electrolytes normal ranges and nursing actions
Lab	Normal range	Low means	High means
Sodium (Na+)	135–145 mEq/L	Hyponatremia: confusion, seizures, headache. Restrict free water; hypertonic saline only for severe symptomatic cases, corrected slowly.	Hypernatremia: thirst, dry mucous membranes, restlessness. Give free water/hypotonic fluids slowly to avoid cerebral edema.
Potassium (K+)	3.5–5.0 mEq/L	Hypokalemia: flat T waves, U waves, muscle weakness, digoxin toxicity risk. Replace K+ — never IV push.	Hyperkalemia: peaked T waves, widened QRS, dysrhythmias. Calcium gluconate protects the heart; insulin + D50, albuterol, kayexalate/dialysis remove it.
Calcium (Ca2+)	9.0–10.5 mg/dL	Hypocalcemia: Trousseau and Chvostek signs, tetany, laryngospasm. Give calcium; keep the airway in view.	Hypercalcemia: lethargy, bone pain, kidney stones, decreased deep tendon reflexes. Hydrate with normal saline and mobilize the patient.
Magnesium (Mg2+)	1.3–2.1 mEq/L	Hypomagnesemia: torsades de pointes, tremors, hyperreflexia. Often accompanies hypokalemia — replace both.	Hypermagnesemia: loss of deep tendon reflexes, respiratory depression, hypotension. Stop the infusion; antidote is calcium gluconate.
Chloride (Cl-)	97–107 mEq/L	Often paired with vomiting and metabolic alkalosis.	Seen with dehydration and hyperchloremic metabolic acidosis from large saline volumes.
Phosphorus	3.0–4.5 mg/dL	Muscle weakness, respiratory failure, refeeding syndrome risk.	Common in kidney failure; moves inversely with calcium.

Reference

Arterial blood gases

Use ROME: Respiratory Opposite, Metabolic Equal. Compare the pH arrow against the CO2 arrow first.

Arterial blood gases normal ranges and nursing actions
Lab	Normal range	Low means	High means
pH	7.35–7.45	Acidosis — look for a high CO2 (respiratory) or low bicarbonate (metabolic).	Alkalosis — look for a low CO2 (respiratory) or high bicarbonate (metabolic).
PaCO2	35–45 mmHg	Blowing off CO2: hyperventilation, anxiety, early sepsis, pain.	Retaining CO2: hypoventilation, COPD, opioid oversedation, atelectasis.
HCO3-	22–26 mEq/L	Metabolic acidosis: DKA, diarrhea, kidney failure, shock.	Metabolic alkalosis: vomiting, nasogastric suction, excess antacids.
PaO2	80–100 mmHg	Hypoxemia — assess airway and oxygenation before anything else.	Usually supplemental oxygen; watch for CO2 retention in chronic COPD.
O2 saturation	95–100%	Below 90% is an emergency in an acute patient; reposition, oxygenate, escalate.	Normal; titrate oxygen down to the lowest effective amount.

Reference

Hematology

Bleeding risk, infection risk, and oxygen-carrying capacity live in this group.

Hematology normal ranges and nursing actions
Lab	Normal range	Low means	High means
WBC	5,000–10,000/mm3	Neutropenia: place on neutropenic precautions, no fresh flowers or raw produce, report any fever immediately.	Infection or inflammation; a left shift means immature neutrophils are being released.
Hemoglobin	12–18 g/dL	Anemia: fatigue, pallor, tachycardia. Pair with hematocrit (roughly 3x hemoglobin).	Dehydration or polycythemia; increases clot risk.
Hematocrit	37–52%	Blood loss, anemia, fluid overload dilution.	Dehydration or chronic hypoxia.
Platelets	150,000–400,000/mm3	Below 50,000 means bleeding precautions; below 20,000 means spontaneous bleeding risk.	Thrombocytosis; increases clotting risk.
INR	0.8–1.1 (2–3 on warfarin)	Subtherapeutic on warfarin — clot risk remains.	Bleeding risk. Antidote for warfarin is vitamin K.
aPTT	30–40 sec (46–70 on heparin)	Subtherapeutic heparin.	Bleeding risk. Antidote for heparin is protamine sulfate.

Reference

Renal, hepatic and metabolic

These numbers drive medication holds and contrast decisions.

Renal, hepatic and metabolic normal ranges and nursing actions
Lab	Normal range	Low means	High means
BUN	10–20 mg/dL	Overhydration, malnutrition, liver disease.	Dehydration, kidney injury, GI bleed, high protein intake.
Creatinine	0.6–1.2 mg/dL	Low muscle mass; rarely clinically urgent.	Kidney impairment — hold metformin and nephrotoxic drugs, question contrast studies.
Glucose (fasting)	70–110 mg/dL	Hypoglycemia: give 15 g fast carbohydrate, recheck in 15 minutes; if unresponsive, D50 or glucagon.	Hyperglycemia: polyuria, polydipsia; DKA if ketones and acidosis are present.
Hemoglobin A1C	Under 5.7% (target under 7% in diabetes)	Reflects tight or excessive glucose control.	Poor 3-month glucose control.
Albumin	3.5–5.0 g/dL	Malnutrition, liver disease, edema; affects protein-bound drug levels.	Usually dehydration.
Total bilirubin	0.1–1.0 mg/dL	Not clinically significant.	Jaundice, liver disease, biliary obstruction, hemolysis.

Reference

Therapeutic drug levels

If the level is above range, hold the dose and notify the provider — that is almost always the correct answer.

Therapeutic drug levels normal ranges and nursing actions
Lab	Normal range	Low means	High means
Digoxin	0.5–2.0 ng/mL	Subtherapeutic; heart failure symptoms may return.	Toxicity: nausea, visual halos, bradycardia. Hypokalemia worsens it. Antidote is digoxin immune Fab.
Lithium	0.6–1.2 mEq/L	Subtherapeutic mood control.	Toxicity: tremor, vomiting, confusion. Dehydration and low sodium raise levels.
Phenytoin	10–20 mcg/mL	Seizure risk remains.	Toxicity: nystagmus, ataxia, slurred speech.
Vancomycin (trough)	10–20 mcg/mL	Inadequate coverage.	Nephrotoxicity and ototoxicity risk; monitor creatinine.
Theophylline	10–20 mcg/mL	Inadequate bronchodilation.	Toxicity: tachycardia, seizures, restlessness.
Acetaminophen	10–30 mcg/mL	Within safe range.	Hepatotoxicity risk. Antidote is acetylcysteine.

Test-day rule

Lab questions are priority questions in disguise

When a stem gives you four abnormal values, the exam is asking which one kills the patient first. Airway and breathing beat circulation; circulation beats metabolic; metabolic beats comfort. A potassium of 6.8 outranks an albumin of 2.9 every time.

Our story characters attach these numbers to a patient — Potassium Pete carries the peaked T waves and the calcium gluconate, Acidotic Andy carries the ABG pattern.

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