What is the normal Hemoglobin (Hgb) range? — Males: 13.5–17.5 g/dL. Females: 12.0–15.5 g/dL. Low = anemia. High = polycythemia or dehydration.

What is the normal Hematocrit (Hct) range? — Males: 41–53%. Females: 36–46%. Hct is approximately 3x the hemoglobin value. Low = anemia or bleeding.

What is the normal Red Blood Cell (RBC) count? — Males: 4.5–5.5 million/µL. Females: 4.0–5.0 million/µL. Low = anemia. High = polycythemia.

What is the normal White Blood Cell (WBC) count? — 4,500–11,000 cells/µL (4.5–11 x10³/µL). Low (leukopenia) = infection risk. High (leukocytosis) = infection, inflammation, or leukemia.

What is the normal Platelet count? — 150,000–400,000/µL (150–400 x10³/µL). Low (thrombocytopenia) = bleeding risk. High (thrombocytosis) = clotting risk.

What is the normal Sodium (Na+) level? — 136–145 mEq/L. Low (hyponatremia) = confusion, seizures. High (hypernatremia) = thirst, dry mucous membranes, confusion.

What is the normal Potassium (K+) level? — 3.5–5.0 mEq/L. Low (hypokalemia) = muscle weakness, cardiac arrhythmias. High (hyperkalemia) = peaked T waves, cardiac arrest risk.

What is the normal Calcium (Ca²+) level? — 8.5–10.5 mg/dL. Low (hypocalcemia) = Trousseau's/Chvostek's signs, tetany. High (hypercalcemia) = "bones, stones, groans, psychic moans."

What is the normal Magnesium (Mg²+) level? — 1.5–2.5 mEq/L. Low (hypomagnesemia) = tremors, seizures, cardiac arrhythmias. High (hypermagnesemia) = respiratory depression, loss of deep tendon reflexes.

What is the normal Phosphorus (PO4) level? — 2.5–4.5 mg/dL. Has an inverse relationship with calcium — when Ca is high, phosphorus is low.

What is the normal Blood Glucose level (fasting)? — 70–100 mg/dL (fasting). 2-hour postprandial: < 140 mg/dL. Hypoglycemia < 70. Hyperglycemia > 126 (fasting, on two occasions = diabetes).

What is the normal Blood Urea Nitrogen (BUN) level? — 10–20 mg/dL. Elevated BUN indicates impaired kidney function, dehydration, or high protein intake.

What is the normal Creatinine level? — Males: 0.7–1.3 mg/dL. Females: 0.6–1.1 mg/dL. Elevated creatinine = impaired kidney function. More specific for renal disease than BUN.

What is the normal BUN:Creatinine ratio and what does it indicate? — Normal ratio: 10:1 to 20:1. Ratio > 20:1 suggests pre-renal causes (dehydration). Ratio < 10:1 suggests intrinsic renal disease.

What is normal eGFR (estimated Glomerular Filtration Rate)? — > 60 mL/min/1.73m². eGFR < 60 for > 3 months indicates chronic kidney disease (CKD). < 15 = kidney failure.

What is the normal Prothrombin Time (PT)? — 11–13.5 seconds. Measures the extrinsic clotting pathway. Elevated in warfarin therapy, liver disease, Vitamin K deficiency.

What is the normal INR and therapeutic range for warfarin? — Normal INR: 0.8–1.2. Therapeutic range for warfarin (most indications): 2.0–3.0. Mechanical heart valves: 2.5–3.5.

What is the normal aPTT and therapeutic range for heparin? — Normal aPTT: 25–35 seconds. Therapeutic heparin range: 60–100 seconds (1.5–2.5 times normal).

What is the normal pH of arterial blood (ABG)? — 7.35–7.45. < 7.35 = acidosis. > 7.45 = alkalosis.

What is the normal PaCO2 (ABG)? — 35–45 mmHg. Controlled by the lungs (respiratory). High CO2 = respiratory acidosis. Low CO2 = respiratory alkalosis.

What is the normal HCO3 (bicarbonate) (ABG)? — 22–26 mEq/L. Controlled by the kidneys (metabolic). Low HCO3 = metabolic acidosis. High HCO3 = metabolic alkalosis.

What is the normal PaO2 (ABG)? — 80–100 mmHg. < 60 mmHg = respiratory failure. Used to assess oxygenation, not acid-base balance.

What is the normal Oxygen Saturation (SpO2)? — 95–100%. SpO2 < 90% is a medical emergency. Target for COPD patients: 88–92% (to avoid suppressing hypoxic drive).

What are the normal Liver Function Tests (LFTs)? — ALT: 7–56 U/L. AST: 10–40 U/L. Alkaline Phosphatase: 44–147 U/L. Total Bilirubin: 0.2–1.2 mg/dL. Elevated = liver disease or damage.

What are the normal Thyroid Function Tests? — TSH: 0.4–4.0 mIU/L (most sensitive test). Free T4: 0.8–1.8 ng/dL. High TSH + Low T4 = hypothyroidism. Low TSH + High T4 = hyperthyroidism.

What is a critical potassium value that requires immediate action? — K+ < 2.5 mEq/L or > 6.0 mEq/L are critical values requiring immediate notification of the provider due to life-threatening cardiac arrhythmia risk.

What is a critical glucose value requiring immediate action? — Blood glucose < 50 mg/dL (severe hypoglycemia) or > 500 mg/dL (DKA/HHS risk) requires immediate intervention.

What is the normal Hemoglobin A1c (HbA1c)? — < 5.7% = normal. 5.7–6.4% = prediabetes. ≥ 6.5% = diabetes. Reflects average blood sugar over the past 2–3 months.

What is the normal Serum Albumin level and clinical significance? — 3.5–5.0 g/dL. Low albumin = malnutrition, liver disease, chronic illness. Also affects drug binding (many medications are albumin-bound).

What are normal Troponin levels and their significance? — Troponin I: < 0.04 ng/mL. Troponin T: < 0.01 ng/mL. Elevated troponin = myocardial infarction (heart attack). The gold standard cardiac biomarker. Rises within 3–4 hours of MI.