Normal serum sodium (Na+) range
Answer: 135–145 mEq/L
Explanation
Sodium is the major extracellular cation and primary determinant of serum osmolality and fluid balance.
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NCLEX-RN: Lab Values and Critical Ranges (University)
Electrolytes: SodiumElectrolytes: PotassiumElectrolytes: CalciumElectrolytes: MagnesiumElectrolytes: PhosphateRenal FunctionGlucose & HbA1cCBCCoagulationABGsLiver EnzymesLipidsCardiac MarkersDrug Levels
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Electrolytes: Sodium
Hyponatremia: causes, signs/symptoms, and priority nursing action
Answer: Causes: excess water intake, SIADH, diuretics, vomiting/diarrhea. S/S: headache, confusion, lethargy, seizures, muscle cramps. Priority action: initiate seizure precautions, restrict free water (if dilutional) or give isotonic/hypertonic saline slowly, monitor neuro status closely.
Explanation
Correct severe hyponatremia slowly (<8–10 mEq/L in 24 hr) to avoid osmotic demyelination syndrome.
Hypernatremia: causes, signs/symptoms, and priority nursing action
Answer: Causes: dehydration, diabetes insipidus, excess sodium intake, Cushing's. S/S: thirst, dry mucous membranes, restlessness, edema, seizures. Priority action: give hypotonic fluids/free water slowly, monitor neuro status, restrict sodium intake.
Explanation
Correct slowly to prevent cerebral edema from fluid shifting too fast into cells.
Electrolytes: Potassium
Normal serum potassium (K+) range
Answer: 3.5–5.0 mEq/L
Explanation
Potassium is critical for cardiac and neuromuscular function; both high and low levels are life-threatening.
Hypokalemia: causes, signs/symptoms, and priority nursing action
Answer: Causes: diuretics, vomiting/diarrhea, insulin administration. S/S: muscle weakness, leg cramps, flattened T waves, U waves, dysrhythmias. Priority action: place on cardiac monitor, replace potassium (oral or diluted IV, NEVER IV push/bolus), monitor for digoxin toxicity.
Explanation
IV potassium must always be diluted and infused via pump, never given by IV push — can cause fatal arrhythmia.
Hyperkalemia: causes, signs/symptoms, and priority nursing action
Answer: Causes: renal failure, tissue trauma, ACE inhibitors, acidosis. S/S: peaked T waves, muscle weakness, cardiac arrest. Priority action: continuous ECG monitoring; give calcium gluconate (cardiac membrane stabilization), insulin + dextrose, sodium polystyrene sulfonate (Kayexalate), and consider dialysis.
Explanation
Calcium gluconate does not lower K+ but protects the heart from dysrhythmia while other treatments shift/remove potassium.
What potassium levels are considered critical/life-threatening?
Answer: K+ <2.5 mEq/L or >6.5 mEq/L
Explanation
These require immediate intervention due to risk of fatal cardiac dysrhythmias.
Electrolytes: Calcium
Normal total serum calcium range
Answer: 8.6–10.2 mg/dL
Explanation
Calcium is vital for bone strength, muscle contraction, nerve conduction, and clotting.
Hypocalcemia: causes, signs/symptoms, and priority nursing action
Answer: Causes: hypoparathyroidism, vitamin D deficiency, renal failure, pancreatitis. S/S: positive Chvostek's and Trousseau's signs, tetany, paresthesias, seizures. Priority action: seizure precautions, administer IV calcium gluconate slowly, monitor cardiac rhythm.
Explanation
Chvostek's = facial twitching when tapping cheek; Trousseau's = carpal spasm with BP cuff inflation — both indicate neuromuscular irritability.
Hypercalcemia: causes, signs/symptoms, and priority nursing action
Answer: Causes: hyperparathyroidism, malignancy, immobility, excess vitamin D. S/S: bone pain, kidney stones, constipation, confusion, decreased DTRs. Priority action: encourage fluids and mobility, give calcitonin/bisphosphonates, monitor for pathologic fractures.
Explanation
Mnemonic: 'bones, stones, groans, and psychiatric overtones.'
Electrolytes: Magnesium
Normal serum magnesium range
Answer: 1.3–2.1 mEq/L
Explanation
Magnesium affects neuromuscular function and cardiac conduction; often inversely related to calcium.
Hypomagnesemia: causes, signs/symptoms, and priority nursing action
Answer: Causes: alcoholism, malnutrition, diarrhea, diuretics. S/S: tremors, hyperreflexia, tetany, dysrhythmias (torsades de pointes). Priority action: seizure precautions, administer magnesium sulfate IV, monitor cardiac rhythm.
Explanation
Low magnesium often causes concurrent hypokalemia and hypocalcemia that won't correct until Mg is replaced.
Hypermagnesemia: causes, signs/symptoms, and priority nursing action
Answer: Causes: renal failure, excess magnesium sulfate administration (e.g., preeclampsia treatment). S/S: loss of deep tendon reflexes, hypotension, bradycardia, respiratory depression. Priority action: stop magnesium infusion, administer calcium gluconate (antidote), monitor respiratory rate and DTRs.
Explanation
Absent patellar reflex is an early warning sign to hold magnesium sulfate in obstetric patients.
Electrolytes: Phosphate
Normal serum phosphate range
Answer: 3.0–4.5 mg/dL
Explanation
Phosphate has an inverse relationship with calcium — as one rises, the other typically falls.
Hypophosphatemia and hyperphosphatemia: causes and key concern
Answer: Hypophosphatemia: causes include malnutrition, alcoholism, refeeding syndrome; S/S muscle weakness, respiratory failure. Hyperphosphatemia: causes include renal failure, tumor lysis syndrome; S/S same as hypocalcemia (tetany) because phosphate binds calcium.
Explanation
Priority action for hyperphosphatemia: administer phosphate binders (e.g., calcium acetate) with meals and monitor calcium levels.
Renal Function
Normal BUN (blood urea nitrogen) range
Answer: 10–20 mg/dL
Explanation
Elevated BUN suggests dehydration, renal impairment, or high protein intake; low BUN suggests overhydration or liver disease.
Normal serum creatinine range
Answer: 0.6–1.2 mg/dL
Explanation
Creatinine is a more specific indicator of renal function than BUN since it is less affected by diet or hydration.
Normal GFR (glomerular filtration rate) and priority nursing concern when low
Answer: Normal GFR: >90 mL/min/1.73m². Priority action when decreased: monitor fluid balance, avoid nephrotoxic drugs (NSAIDs, contrast dye, aminoglycosides), assess for signs of fluid overload and uremia.
Explanation
GFR <60 for 3+ months indicates chronic kidney disease; GFR <15 indicates kidney failure requiring dialysis.
Glucose & HbA1c
Normal fasting blood glucose range
Answer: 70–99 mg/dL
Explanation
Prediabetes: 100–125 mg/dL fasting; diabetes: ≥126 mg/dL fasting on two occasions.
Hypoglycemia: threshold, symptoms, and priority nursing action
Answer: Glucose <70 mg/dL. S/S: shakiness, diaphoresis, confusion, tachycardia. Priority action: Rule of 15 — give 15g fast-acting carbohydrate, recheck glucose in 15 minutes, repeat if still low; if unconscious give IV dextrose or IM glucagon.
Explanation
Never give oral glucose to an unconscious patient due to aspiration risk.
Normal HbA1c and diabetes diagnostic/goal values
Answer: Normal: <5.7%. Prediabetes: 5.7–6.4%. Diabetes diagnosis: ≥6.5%. Treatment goal for most diabetics: <7%.
Explanation
HbA1c reflects average blood glucose control over the past ~2–3 months.
CBC
Normal hemoglobin and hematocrit values
Answer: Hemoglobin: males 14–18 g/dL, females 12–16 g/dL. Hematocrit: males 42–52%, females 37–47%.
Explanation
Hematocrit is roughly 3x the hemoglobin value; both decrease with anemia/blood loss and increase with dehydration or polycythemia.
Low hemoglobin/hematocrit: priority nursing action
Answer: Assess for signs of hypoxia/bleeding, monitor vital signs, administer oxygen and blood transfusion as ordered, minimize exertion.
Explanation
Symptomatic anemia (fatigue, tachycardia, pallor, dyspnea) requires prompt intervention to prevent cardiac compromise.
Normal WBC count and what high/low values indicate
Answer: Normal: 5,000–10,000/mm³. High (leukocytosis): infection, inflammation, leukemia. Low (leukopenia): bone marrow suppression, chemotherapy, viral infection.
Explanation
Priority action with leukopenia: initiate neutropenic precautions (private room, hand hygiene, avoid fresh flowers/raw foods, monitor for fever).
Normal platelet count and critical bleeding thresholds
Answer: Normal: 150,000–400,000/mm³. Risk of bleeding with trauma <50,000/mm³. Risk of spontaneous bleeding <20,000/mm³.
Explanation
Priority action: implement bleeding precautions (soft toothbrush, electric razor, avoid IM injections/NSAIDs, monitor for petechiae or occult blood).
Coagulation
Normal PT and INR values, and therapeutic INR range on warfarin
Answer: PT: 11–12.5 seconds. INR: 0.8–1.1 (normal). Therapeutic INR on warfarin: 2.0–3.0 (2.5–3.5 for mechanical heart valves).
Explanation
Antidote for warfarin toxicity/overdose: Vitamin K (phytonadione).
Normal aPTT value and therapeutic range on heparin
Answer: Normal aPTT: 25–35 seconds. Therapeutic on heparin: 1.5–2.5 times the control value (~60–80 seconds).
Explanation
Antidote for heparin toxicity/overdose: Protamine sulfate.
Priority nursing action for a patient on anticoagulants with abnormal elevated coag values
Answer: Monitor for bleeding (gums, stool, urine, bruising), hold/adjust dose per provider order, have antidote available (vitamin K for warfarin, protamine for heparin), implement bleeding precautions.
Explanation
Always correlate lab value with the specific anticoagulant the patient is receiving before intervening.
ABGs
Normal ABG values (pH, PaCO2, HCO3, PaO2, SaO2)
Answer: pH: 7.35–7.45; PaCO2: 35–45 mmHg; HCO3: 22–26 mEq/L; PaO2: 80–100 mmHg; SaO2: 95–100%.
Explanation
Use the ROME method (Respiratory Opposite, Metabolic Equal) to interpret acid-base disorders: compare pH direction to CO2 (opposite = respiratory) or HCO3 (equal = metabolic).
Respiratory acidosis vs. respiratory alkalosis: values and causes
Answer: Respiratory acidosis: pH <7.35, PaCO2 >45 — caused by hypoventilation (COPD, opioid overdose, sedation). Respiratory alkalosis: pH >7.45, PaCO2 <35 — caused by hyperventilation (anxiety, pain, high altitude).
Explanation
Priority action for respiratory acidosis: improve ventilation (bronchodilators, positioning, reverse sedation). For alkalosis: have patient breathe into a paper bag or slow breathing rate.
Metabolic acidosis vs. metabolic alkalosis: values and causes
Answer: Metabolic acidosis: pH <7.35, HCO3 <22 — caused by DKA, renal failure, diarrhea. Metabolic alkalosis: pH >7.45, HCO3 >26 — caused by vomiting, NG suction, excess antacid/bicarbonate use.
Explanation
Priority action for metabolic acidosis: treat underlying cause (e.g., insulin for DKA); for metabolic alkalosis, replace fluids/electrolytes (especially potassium and chloride) lost from vomiting/suction.
Liver Enzymes
Normal liver enzyme values: ALT and AST
Answer: ALT: 7–56 U/L. AST: 10–40 U/L.
Explanation
Both rise with hepatocellular injury (hepatitis, cirrhosis, acetaminophen toxicity); ALT is more liver-specific while AST also rises with cardiac/muscle injury.
Priority nursing action for significantly elevated liver enzymes
Answer: Monitor for signs of liver failure (jaundice, ascites, bleeding, confusion/encephalopathy), hold hepatotoxic medications, monitor coagulation studies and ammonia level.
Explanation
The liver produces clotting factors, so impaired function increases bleeding risk.
Lipids
Desirable lipid panel values (total cholesterol, LDL, HDL, triglycerides)
Answer: Total cholesterol: <200 mg/dL. LDL ('bad'): <100 mg/dL optimal. HDL ('good'): >60 mg/dL protective (men >40, women >50). Triglycerides: <150 mg/dL.
Explanation
Elevated LDL and triglycerides increase cardiovascular/atherosclerosis risk; priority nursing action is patient teaching on diet, exercise, and statin adherence.
Cardiac Markers
Cardiac markers: troponin, CK-MB, and BNP — normal values and significance
Answer: Troponin: normal <0.04 ng/mL, rises within hours of MI and stays elevated 7–10 days — most specific marker for myocardial injury. CK-MB: normal 0–25 U/L, rises with cardiac muscle damage. BNP: normal <100 pg/mL, elevated in heart failure proportional to severity.
Explanation
Priority action with elevated troponin: notify provider immediately, continuous cardiac monitoring, prepare for possible cath lab/PCI.
Drug Levels
Digoxin: therapeutic range, toxicity signs, and priority nursing action
Answer: Therapeutic range: 0.5–2.0 ng/mL. Toxicity signs: nausea/vomiting, visual disturbances (halos, yellow-green vision), bradycardia, dysrhythmias. Priority action: hold dose, check apical pulse before administration (hold if <60 bpm), check potassium level (hypokalemia increases toxicity risk), notify provider.
Explanation
Digoxin toxicity is potentiated by hypokalemia and hypercalcemia — always verify electrolytes before giving digoxin.
Lithium: therapeutic range, toxicity threshold, and priority nursing action
Answer: Therapeutic range: 0.6–1.2 mEq/L. Toxicity: >1.5 mEq/L (severe toxicity >2.0). S/S of toxicity: tremors, ataxia, confusion, vomiting. Priority action: hold dose, ensure adequate hydration and sodium intake, monitor levels closely.
Explanation
Low sodium intake or dehydration increases lithium reabsorption and risk of toxicity.
Phenytoin: therapeutic range and toxicity signs
Answer: Therapeutic range: 10–20 mcg/mL. Toxicity signs: nystagmus, ataxia, slurred speech, confusion. Priority action: hold dose, monitor neuro status, check level before next dose.
Explanation
Phenytoin is used to prevent/treat seizures; gingival hyperplasia is a long-term side effect to teach patients about (oral hygiene).
Theophylline: therapeutic range and toxicity signs
Answer: Therapeutic range: 10–20 mcg/mL. Toxicity signs: nausea, tachycardia, seizures, dysrhythmias. Priority action: hold dose, monitor cardiac rhythm, notify provider for levels above range.
Explanation
Theophylline toxicity risk increases with certain drug interactions (e.g., cimetidine, ciprofloxacin) and smoking status changes.
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