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Memory tricks for normal ranges and what they mean

Lab values connect anatomy to clinical medicine. Knowing normal ranges — and what happens when they fall outside them — helps you understand which organ system is involved. These memory tricks help the numbers stick.

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🧪 Lab Values & Diagnostics

Memory Tricks

Proven Mnemonics & Acronyms — fast to learn, hard to forget.

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Complete Blood Count — CBC
7-14-42-150 — WBC · Hgb (F) · Hct · Platelets
Normal CBC reference values to memorize
Key CBC normal ranges — the most ordered lab test in medicine
WBC: 4,500–11,000/μL. High = infection/inflammation/leukemia. Low = bone marrow suppression. Hemoglobin: Male 13.5–17.5 g/dL, Female 12–16 g/dL. Low = anemia. Hematocrit: ~3× the hemoglobin value. Platelets: 150,000–400,000/μL. Low (thrombocytopenia) = bleeding risk. High (thrombocytosis) = clotting risk. Memory: think 7.5-15-45-250 as rough midpoints for WBC (thousands), Hgb, Hct, Platelets (thousands).
WBC
4,500–11,000/μL. Neutrophils 60–70%, Lymphocytes 20–30%.
Hemoglobin
M: 13.5–17.5 g/dL. F: 12–16 g/dL. Low = anemia.
Hematocrit
M: 41–53%. F: 36–46%. Rule of 3: Hct ≈ Hgb × 3.
Platelets
150–400 × 10³/μL. <100 = thrombocytopenia. <50 = significant bleeding risk.
MCV
80–100 fL. Low = microcytic (iron deficiency). High = macrocytic (B12/folate).
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🃏 Complete Blood Count — CBC
CBC — normal WBC, hemoglobin, hematocrit, platelets?
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🃏 Answer
7-14-42-150 — WBC · Hgb (F) · Hct · Platelets
WBC4,500–11,000/μL. Neutrophils 60–70%, Lymphocytes 20–30%.
HemoglobinM: 13.5–17.5 g/dL. F: 12–16 g/dL. Low = anemia.
HematocritM: 41–53%. F: 36–46%. Rule of 3: Hct ≈ Hgb × 3.
Platelets150–400 × 10³/μL. <100 = thrombocytopenia. <50 = significant bleeding risk.
MCV80–100 fL. Low = microcytic (iron deficiency). High = macrocytic (B12/folate).
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Basic Metabolic Panel — BMP
Na 140 · K 4 · Cl 100 · CO2 24 · BUN 15 · Cr 1 · Glucose 90
Seven key electrolyte and metabolic normal values
BMP normal ranges — the "fishbone" panel ordered every day in hospitals
Sodium (Na+): 136–145 mEq/L. Low = hyponatremia (confusion, seizures). High = hypernatremia (dehydration). Potassium (K+): 3.5–5.0 mEq/L. Dangerous outside this range — cardiac arrhythmias. Chloride: 98–106 mEq/L. Bicarbonate (CO2): 22–29 mEq/L. Low = acidosis. BUN (blood urea nitrogen): 7–25 mg/dL. High = kidney or liver issue. Creatinine: 0.6–1.2 mg/dL. High = kidney dysfunction. Glucose: 70–100 mg/dL fasting.
Na+ 136–145
Hyponatremia: confusion, seizures. Hypernatremia: thirst, dehydration.
K+ 3.5–5.0
Hypokalemia: muscle weakness, arrhythmia. Hyperkalemia: peaked T waves, cardiac arrest.
BUN/Cr ratio
>20:1 = pre-renal (dehydration). <10:1 = intrinsic renal disease.
Glucose 70–100
Fasting. >126 twice = diabetes. <70 = hypoglycemia (shakiness, confusion).
HbA1c
3-month average glucose. <5.7% normal. 5.7–6.4% pre-diabetes. ≥6.5% diabetes.
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🃏 Basic Metabolic Panel — BMP
BMP — the normal values?
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🃏 Answer
Na 140 · K 4 · Cl 100 · CO2 24 · BUN 15 · Cr 1 · Glucose 90
Na+ 136–145Hyponatremia: confusion, seizures. Hypernatremia: thirst, dehydration.
K+ 3.5–5.0Hypokalemia: muscle weakness, arrhythmia. Hyperkalemia: peaked T waves, cardiac arrest.
BUN/Cr ratio>20:1 = pre-renal (dehydration). <10:1 = intrinsic renal disease.
Glucose 70–100Fasting. >126 twice = diabetes. <70 = hypoglycemia (shakiness, confusion).
HbA1c3-month average glucose. <5.7% normal. 5.7–6.4% pre-diabetes. ≥6.5% diabetes.
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Liver Function Tests — LFTs
ALT AST ALP — All Liver Tests · ALT most specific for liver
ALT · AST · ALP · Bilirubin · Albumin · PT/INR
Liver function test panel — what each value tells you about the liver
ALT (alanine aminotransferase): most specific for liver damage. Normal 7–56 U/L. AST (aspartate aminotransferase): liver and heart/muscle. Normal 10–40 U/L. AST/ALT ratio >2:1 suggests alcoholic hepatitis. ALP (alkaline phosphatase): liver and bone. High in cholestasis and Paget's disease. Bilirubin: total 0.1–1.2 mg/dL. High = jaundice. Albumin: 3.5–5.0 g/dL. Low = chronic liver disease or malnutrition. PT/INR: measures clotting factor synthesis — elevated in liver failure.
ALT
Most liver-specific. High = hepatitis, fatty liver, drug toxicity.
AST
Liver + heart/muscle. AST:ALT >2:1 = alcoholic hepatitis. >3:1 = strongly suggests alcohol.
ALP
High in cholestasis (bile flow obstruction) and bone disease (Paget's).
Bilirubin
Direct (conjugated) = liver/post-hepatic. Indirect (unconjugated) = pre-hepatic/hemolysis.
INR
Normal ~1.0. Elevated = liver disease or warfarin. Measures extrinsic pathway.
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🃏 Liver Function Tests — LFTs
Liver function tests — which is most liver-specific?
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🃏 Answer
ALT AST ALP — All Liver Tests · ALT most specific for liver
ALTMost liver-specific. High = hepatitis, fatty liver, drug toxicity.
ASTLiver + heart/muscle. AST:ALT >2:1 = alcoholic hepatitis. >3:1 = strongly suggests alcohol.
ALPHigh in cholestasis (bile flow obstruction) and bone disease (Paget's).
BilirubinDirect (conjugated) = liver/post-hepatic. Indirect (unconjugated) = pre-hepatic/hemolysis.
INRNormal ~1.0. Elevated = liver disease or warfarin. Measures extrinsic pathway.
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Arterial Blood Gas — ABG
pH 7.4 · PaCO2 40 · PaO2 80-100 · HCO3 24
Normal ABG values — assess respiratory and metabolic function
ABG normal values and how to interpret acid-base disorders
pH 7.35–7.45 (normal = 7.40). PaCO2 35–45 mmHg (respiratory component). PaO2 80–100 mmHg (oxygenation). HCO3 22–26 mEq/L (metabolic component). To interpret: pH low = acidosis. pH high = alkalosis. If PaCO2 is abnormal = respiratory cause. If HCO3 is abnormal = metabolic cause. Low pH + high CO2 = respiratory acidosis (COPD). Low pH + low HCO3 = metabolic acidosis (DKA). High pH + low CO2 = respiratory alkalosis (hyperventilation). High pH + high HCO3 = metabolic alkalosis (vomiting).
pH <7.35
Acidosis. Check CO2 and HCO3 to determine respiratory vs metabolic.
pH >7.45
Alkalosis. Check CO2 and HCO3 to determine respiratory vs metabolic.
Resp acidosis
High CO2 — hypoventilation, COPD, opioid overdose, respiratory failure.
Metabolic acidosis
Low HCO3 — DKA, lactic acidosis, renal failure, diarrhea.
Metabolic alkalosis
High HCO3 — vomiting, nasogastric suction, diuretic use.
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🃏 Arterial Blood Gas — ABG
ABG — the normal values?
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🃏 Answer
pH 7.4 · PaCO2 40 · PaO2 80-100 · HCO3 24
pH <7.35Acidosis. Check CO2 and HCO3 to determine respiratory vs metabolic.
pH >7.45Alkalosis. Check CO2 and HCO3 to determine respiratory vs metabolic.
Resp acidosisHigh CO2 — hypoventilation, COPD, opioid overdose, respiratory failure.
Metabolic acidosisLow HCO3 — DKA, lactic acidosis, renal failure, diarrhea.
Metabolic alkalosisHigh HCO3 — vomiting, nasogastric suction, diuretic use.
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Cardiac Markers
Troponin = Gold standard · CK-MB = Early · BNP = Heart failure
Troponin I/T · CK-MB · BNP/NT-proBNP · Myoglobin
Cardiac biomarkers — what each one indicates and when it peaks
Troponin I and T: most sensitive and specific for myocardial infarction. Rises 3–6 hours after MI, peaks 24 hours, remains elevated 7–14 days. Gold standard for MI diagnosis. CK-MB: rises 3–6 hours, peaks 24 hours, returns to normal in 3 days — useful for detecting reinfarction. BNP/NT-proBNP: released by ventricular myocytes under pressure — elevated in heart failure. BNP >100 pg/mL suggests heart failure. Myoglobin: rises earliest (1–3 hours) but not specific for heart — also elevated in muscle injury.
Troponin
Gold standard MI marker. Rises 3–6 hr, peaks 24 hr, stays elevated 7–14 days.
CK-MB
Returns to normal in 3 days — useful for detecting re-infarction after initial MI.
BNP
>100 pg/mL = heart failure likely. >400 pg/mL = strong evidence. Used to rule out HF.
Myoglobin
First to rise (1–3 hr) but not heart-specific. Elevated in any muscle injury.
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🃏 Cardiac Markers
Cardiac markers — troponin vs CK-MB vs BNP?
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🃏 Answer
Troponin = Gold standard · CK-MB = Early · BNP = Heart failure
TroponinGold standard MI marker. Rises 3–6 hr, peaks 24 hr, stays elevated 7–14 days.
CK-MBReturns to normal in 3 days — useful for detecting re-infarction after initial MI.
BNP>100 pg/mL = heart failure likely. >400 pg/mL = strong evidence. Used to rule out HF.
MyoglobinFirst to rise (1–3 hr) but not heart-specific. Elevated in any muscle injury.
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Thyroid Labs
High TSH + Low T4 = Hypothyroid · Low TSH + High T4 = Hyperthyroid
TSH 0.4–4.0 mIU/L · Free T4 0.8–1.8 ng/dL
Thyroid lab interpretation — the inverse relationship that explains everything
TSH is the most sensitive thyroid test — it changes before T4 does. Normal TSH: 0.4–4.0 mIU/L. Normal free T4: 0.8–1.8 ng/dL. High TSH + Low T4 = Primary hypothyroidism (thyroid gland failing). Low TSH + High T4 = Hyperthyroidism (too much thyroid hormone feeding back to suppress TSH). Low TSH + Low T4 = Central hypothyroidism (pituitary/hypothalamus problem). TSH is always the first test ordered — a normal TSH essentially rules out thyroid disease.
High TSH + Low T4
Primary hypothyroidism — thyroid gland not responding. Treat with levothyroxine.
Low TSH + High T4
Hyperthyroidism — excess hormone suppresses TSH. Graves' disease most common.
High TSH + Normal T4
Subclinical hypothyroidism — early, may progress to overt hypothyroidism.
Low TSH + Low T4
Central hypothyroidism — pituitary or hypothalamus not signaling thyroid.
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🃏 Thyroid Labs
Thyroid labs — what do the TSH and T4 patterns mean?
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🃏 Answer
High TSH + Low T4 = Hypothyroid · Low TSH + High T4 = Hyperthyroid
High TSH + Low T4Primary hypothyroidism — thyroid gland not responding. Treat with levothyroxine.
Low TSH + High T4Hyperthyroidism — excess hormone suppresses TSH. Graves' disease most common.
High TSH + Normal T4Subclinical hypothyroidism — early, may progress to overt hypothyroidism.
Low TSH + Low T4Central hypothyroidism — pituitary or hypothalamus not signaling thyroid.
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Coagulation Studies
PT/INR = Extrinsic (1, 2, 5, 7, 10) · PTT = Intrinsic (8, 9, 11, 12)
PT tests extrinsic pathway · PTT tests intrinsic pathway
Coagulation tests — which clotting factors each one measures
PT (prothrombin time): measures extrinsic pathway. Factors I, II, V, VII, X. Normal 11–13 seconds. INR normalizes PT between labs — normal 0.8–1.2. Elevated in liver disease and warfarin use. PTT (partial thromboplastin time): measures intrinsic pathway. Factors VIII, IX, XI, XII. Normal 25–35 seconds. Elevated in hemophilia (factor VIII or IX deficiency) and heparin use. Bleeding time: platelet function. Thrombin time: fibrinogen function.
PT/INR elevated
Liver disease (can't make clotting factors) or warfarin. Extrinsic pathway.
PTT elevated
Hemophilia A (VIII) or B (IX), or heparin therapy. Intrinsic pathway.
Both elevated
DIC (disseminated intravascular coagulation) or severe liver failure.
Warfarin
Inhibits vitamin K-dependent factors (II, VII, IX, X). Monitored with INR.
Heparin
Activates antithrombin III. Monitored with PTT. Reversed by protamine sulfate.
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🃏 Coagulation Studies
Coagulation — what do PT/INR and PTT measure?
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🃏 Answer
PT/INR = Extrinsic (1, 2, 5, 7, 10) · PTT = Intrinsic (8, 9, 11, 12)
PT/INR elevatedLiver disease (can't make clotting factors) or warfarin. Extrinsic pathway.
PTT elevatedHemophilia A (VIII) or B (IX), or heparin therapy. Intrinsic pathway.
Both elevatedDIC (disseminated intravascular coagulation) or severe liver failure.
WarfarinInhibits vitamin K-dependent factors (II, VII, IX, X). Monitored with INR.
HeparinActivates antithrombin III. Monitored with PTT. Reversed by protamine sulfate.
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Urinalysis
CGPBKN — Color · Glucose · Protein · Blood · Ketones · Nitrites
Six key urinalysis findings and what each indicates
Urinalysis interpretation — what abnormal findings suggest
Normal urine: clear, pale yellow, pH 4.5–8, specific gravity 1.001–1.035. Glucose in urine (glucosuria): blood glucose >180 mg/dL — diabetes. Protein (proteinuria): kidney disease, nephrotic syndrome. Blood (hematuria): UTI, kidney stones, cancer. Ketones: starvation, DKA, low-carb diet. Nitrites: bacterial infection (gram-negative bacteria convert nitrates to nitrites — positive = UTI). WBCs in urine: UTI or kidney inflammation. Casts: RBC casts = glomerulonephritis. WBC casts = pyelonephritis.
Glucose
Blood glucose >180 mg/dL overwhelms renal threshold. Diabetes or pregnancy.
Protein
>300 mg/day = significant. Nephrotic syndrome: >3.5 g/day + edema + low albumin.
Blood
Gross hematuria — UTI, stones, trauma, cancer. Always warrants investigation.
Nitrites + WBCs
UTI — most commonly E. coli. Treat with antibiotics.
RBC casts
Pathognomonic for glomerulonephritis — RBCs squeezed through damaged glomeruli.
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🃏 Urinalysis
CGPBKN
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🃏 Answer
CGPBKN — Color · Glucose · Protein · Blood · Ketones · Nitrites
GlucoseBlood glucose >180 mg/dL overwhelms renal threshold. Diabetes or pregnancy.
Protein>300 mg/day = significant. Nephrotic syndrome: >3.5 g/day + edema + low albumin.
BloodGross hematuria — UTI, stones, trauma, cancer. Always warrants investigation.
Nitrites + WBCsUTI — most commonly E. coli. Treat with antibiotics.
RBC castsPathognomonic for glomerulonephritis — RBCs squeezed through damaged glomeruli.
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Anemia Classification
MCV tells the story — Small · Normal · Large
Microcytic (MCV <80) · Normocytic (80–100) · Macrocytic (MCV >100)
Three types of anemia by MCV — the fastest way to narrow the diagnosis
MCV (mean corpuscular volume) is the key to classifying anemia. Microcytic (MCV <80): small red cells. Causes: iron deficiency (most common), thalassemia, lead poisoning, chronic disease. Remember: ITS MCV — Iron deficiency, Thalassemia, Sideroblastic, Microcytic. Normocytic (MCV 80–100): normal size. Causes: acute blood loss, hemolysis, anemia of chronic disease, early iron deficiency. Macrocytic (MCV >100): large red cells. Causes: B12 deficiency, folate deficiency, liver disease, hypothyroidism, alcohol.
Microcytic <80
Iron deficiency (most common globally). Low ferritin. High TIBC.
Normocytic 80–100
Acute blood loss, hemolysis, chronic disease, CKD (low EPO).
Macrocytic >100
B12 deficiency (neurological symptoms), folate deficiency, alcohol, liver disease.
Iron deficiency
Low ferritin, low iron, high TIBC. Most common anemia worldwide.
B12 deficiency
Low B12, elevated MMA and homocysteine. Neurological damage if untreated.
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🃏 Anemia Classification
Anemia — how does MCV classify it?
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MCV tells the story — Small · Normal · Large
Microcytic <80Iron deficiency (most common globally). Low ferritin. High TIBC.
Normocytic 80–100Acute blood loss, hemolysis, chronic disease, CKD (low EPO).
Macrocytic >100B12 deficiency (neurological symptoms), folate deficiency, alcohol, liver disease.
Iron deficiencyLow ferritin, low iron, high TIBC. Most common anemia worldwide.
B12 deficiencyLow B12, elevated MMA and homocysteine. Neurological damage if untreated.
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🎓 Common Exam Questions
📋 Study note: Lab value ranges shown here are standard reference ranges used in medical education. Normal ranges can vary slightly between laboratories and institutions. These values are for learning purposes — always refer to your course materials and institutional references for clinical application.