Labs and Abnormal Value Interpretation

Review the high-yield NCLEX lab values from the session compiler with low/high findings and priority nursing actions.

Lab interpretation table

Study ranges are broad references. Use school and facility ranges for exams and clinical work.

needs review

Lab	Normal range	Meaning	Low / high clues	Priority actions
Sodium	135-145 mEq/L	Water balance and neurologic status. Sodium swells or shrinks the brain.	Low: Confusion, Headache, Seizures High: Thirst, Dry mucosa, Restlessness	Institute seizure precautions for severe symptoms. Trend correction rate as ordered.
Potassium	3.5-5.0 mEq/L	Cardiac conduction and muscle function. K kills.	Low: Weakness, U waves, Constipation High: Peaked T waves, Weakness, Cardiac arrest risk	Place symptomatic or critical abnormal values on cardiac monitor. Never IV push potassium.
Calcium	8.5-10.5 mg/dL	Bone, clotting, neuromuscular excitability, and cardiac conduction. Low calcium is twitchy; high calcium is slow and stony.	Low: Tetany, Tingling, Seizures High: Kidney stones, Constipation, Confusion	Watch airway spasm/seizures when low. Promote hydration and safety when high if allowed.
Magnesium	1.7-2.2 mg/dL	Neuromuscular calming and cardiac rhythm stability. Magnesium calms; too much shuts down.	Low: Tremors, Seizures, Torsades risk High: Absent reflexes, Respiratory depression, Hypotension	Monitor reflexes and respirations during magnesium infusion. Keep calcium gluconate available when ordered.
BUN / Creatinine	BUN 10-20 mg/dL; creatinine about 0.6-1.3 mg/dL	Kidney perfusion and filtration trends. Creatinine is kidney filter trend.	High: Dehydration, AKI/CKD, Medication dosing risk	Trend urine output and nephrotoxic medication risk. Escalate rising creatinine with low urine output.
WBC	4,500-11,000/mm3	Infection, inflammation, marrow response, or immunosuppression.	Low: Neutropenia infection risk High: Infection/inflammation, Stress response	Use neutropenic precautions when indicated. Trend with fever and cultures.
Hgb / Hct	Hgb about 12-18 g/dL; Hct about 36-54%	Oxygen-carrying capacity and bleeding/anemia trend.	Low: Fatigue, Dyspnea, Bleeding/anemia High: Dehydration or polycythemia concern	Assess active bleeding and oxygenation. Trend after GI bleed, trauma, or surgery.
Platelets	150,000-400,000/mm3	Primary clot formation.	Low: Bruising, Petechiae, Bleeding High: Clot risk in selected contexts	Bleeding precautions when low. Avoid IM injections if severely low per policy.
PT / INR	PT about 11-13.5 sec; INR about 0.8-1.1 unless anticoagulated	Extrinsic clotting pathway; warfarin monitoring context. Warfarin watches PT/INR.	High: Bleeding risk, Liver dysfunction, Warfarin effect	Assess bleeding and medication safety. Know vitamin K reversal context for warfarin.
aPTT	About 25-35 sec unless anticoagulated	Intrinsic clotting pathway; heparin monitoring context. Heparin has two Ps in aPTT.	High: Bleeding risk, Heparin effect	Assess bleeding with heparin therapy. Know protamine reversal context for heparin.
Glucose	Fasting about 70-99 mg/dL	Immediate brain fuel and diabetes control.	Low: Sweaty, Shaky, Confused, Seizure High: Polyuria, Thirst, DKA/HHS risk	Treat symptomatic hypoglycemia promptly. Check ketones/acid-base when DKA suspected.
Albumin	3.5-5.0 g/dL	Protein/nutrition status and oncotic pressure.	Low: Edema, Poor wound healing, Ascites risk	Assess nutrition, liver disease, kidney loss, and wound risk.
Ammonia	Varies by lab; commonly about 15-45 mcg/dL	Liver detoxification and encephalopathy trend. Ammonia clouds the brain.	High: Confusion, Asterixis, Lethargy	Assess airway/safety and lactulose response when ordered.
Troponin	Lab-specific; normally very low/undetectable	Myocardial injury marker.	High: MI/ACS concern, Other myocardial strain/injury contexts	Pair with symptoms and ECG. Escalate chest pain plus elevated/rising value.
BNP	Lab-specific; often <100 pg/mL used as a low-risk reference	Heart stretch and heart failure support marker.	High: Heart failure exacerbation context, Volume/pressure overload	Assess dyspnea, edema, weight, and lung sounds with the value.
ABG pH	7.35-7.45	Overall acid-base direction.	Low: Acidosis High: Alkalosis	Use pH first to decide acid versus alkalotic state.
PaCO2	35-45 mm Hg	Respiratory acid controlled by ventilation. CO2 equals respiratory.	Low: Respiratory alkalosis direction High: Respiratory acidosis direction	Assess ventilation, airway, and breathing when PaCO2 drives the problem.
HCO3	22-26 mEq/L	Metabolic base controlled mainly by kidneys. HCO3 equals metabolic.	Low: Metabolic acidosis direction High: Metabolic alkalosis direction	Look for DKA, renal failure, GI losses, or vomiting based on direction.
Vitamin D	Lab-specific; commonly 25(OH)D about 20-50 ng/mL	Vitamin D status related to calcium absorption and bone mineralization. D helps deposit calcium in bone.	Low: Rickets, Osteomalacia, Bone pain, Muscle weakness High: Hypercalcemia, Nausea, Confusion, Kidney stone risk	Interpret with calcium, phosphorus, kidney function, diet, and ordered supplementation plan.
Vitamin B12	Lab-specific; often about 200-900 pg/mL	Cobalamin status for red blood cell production and neurologic function. B12 is blood plus nerves.	Low: Megaloblastic anemia, Paresthesias, Gait changes, Glossitis	Assess neurologic symptoms and anemia; review vegan diet, gastric surgery, metformin, and long-term acid suppression risk.
Ferritin	Lab-specific; reflects iron stores.	Iron storage marker used in anemia workups. Ferritin is the iron pantry.	Low: Iron deficiency, Fatigue, Pallor, Restless legs in some clients High: Inflammation context, Iron overload context	Interpret with CBC, serum iron/TIBC when ordered, bleeding history, pregnancy status, and diet.
Serum phosphorus	About 2.5-4.5 mg/dL	Mineral related to bone health, energy transfer, renal function, and calcium balance. Phos pairs with calcium and kidneys.	Low: Weakness, Bone pain risk, Refeeding-risk context High: Kidney disease context, Low calcium risk	Interpret with calcium, kidney function, diet, phosphate binders, and refeeding risk.
Serum iron	Lab-specific; often about 60-170 mcg/dL	Circulating iron used with ferritin, TIBC, CBC, and bleeding history in anemia workups. Serum iron is one piece of the anemia puzzle.	Low: Iron deficiency anemia, Fatigue, Pallor High: Iron overload context, Excess supplementation context	Interpret with ferritin, TIBC, CBC, pregnancy status, bleeding risk, and supplement history.
Serum folate	Lab-specific; often about 3-20 ng/mL	Folate status related to DNA synthesis, RBC formation, and fetal neural tube development. Folate forms fetal tube and fast cells.	Low: Megaloblastic anemia, Pregnancy neural tube defect risk	Assess pregnancy potential, diet, alcohol use, and medications; pair with B12 evaluation when ordered.
Albumin	Lab-specific; often about 3.4-5.4 g/dL	Protein made by the liver; affected by nutrition, inflammation, liver disease, kidney loss, hydration, and illness. Albumin holds fluid in vessels.	Low: Edema risk, Poor healing risk, Inflammation or liver/kidney context	Do not interpret as nutrition alone; assess edema, liver/kidney status, inflammation, intake, and wounds.
Prealbumin	Lab-specific; often about 15-36 mg/dL	Shorter half-life nutrition-related marker affected by inflammation, kidney/liver status, and acute illness. Prealbumin changes sooner, but context still rules.	Low: Malnutrition risk context, Inflammation context	Trend with intake, weight, inflammation, wounds, and clinical condition rather than using alone.
Serum zinc	Lab-specific; often about 70-120 mcg/dL	Trace mineral related to immune function, wound healing, growth, and taste/smell cues. Zinc zips wounds closed.	Low: Delayed wound healing, Hair loss, Diarrhea, Impaired immune function High: Nausea/vomiting, Copper deficiency risk	Assess wounds, intake, GI losses, supplements, and copper risk when high-dose zinc is used.