Lab Values Nursing Guide 2026
⚕️ Medical Disclaimer: This content is for educational purposes only and is intended for licensed healthcare professionals. It does not constitute medical advice and should not replace clinical judgment, facility protocols, or physician orders. Always verify medications, doses, and procedures with your institution's guidelines.
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Normal reference ranges, critical/panic values, and clinical interpretation for every major lab panel — the essential nursing reference for interpreting results and knowing when to call the provider.
1. Complete Blood Count (CBC)
| Lab | Normal Range | Critical Low | Critical High | Clinical Pearls |
|---|
| Hemoglobin (Hgb) | Male: 13.5–17.5 g/dL; Female: 12.0–15.5 g/dL | <7 g/dL | >20 g/dL | Transfuse threshold typically <7 g/dL (8 g/dL with cardiac disease); Hgb drops 1g/dL per unit lost but may not reflect acute bleed for hours |
| Hematocrit (Hct) | Male: 41–53%; Female: 36–46% | <21% | >60% | Hct = ~3× Hgb; high Hct (polycythemia) → increased viscosity, clot risk |
| WBC | 4.5–11.0 × 10³/mcL | <2.0 | >30 | Neutropenia: ANC <1,500 (mild), <500 (severe) → infection risk; leukocytosis >11k → infection, stress, steroids, leukemia |
| Platelets (PLT) | 150–400 × 10³/mcL | <50 (bleeding risk); <20 (spontaneous bleed) | >1,000 | <50k: avoid invasive procedures; <100k: modify anticoagulation; Heparin (HIT): drop >50% day 5–14 |
| MCV (Mean Corpuscular Volume) | 80–100 fL | <70 | >115 | Low MCV = microcytic (iron deficiency, thalassemia); High MCV = macrocytic (B12/folate deficiency, liver disease, alcohol, hypothyroidism) |
2. ANC Calculation
ANC = WBC × (% Segs + % Bands) / 100
Example: WBC 3.0, 40% segs, 10% bands → ANC = 3.0 × (40+10)/100 = 1.5 (borderline neutropenia)
ANC <500 = severe neutropenia → neutropenic precautions, reverse isolation, no fresh flowers/plants, avoid raw foods
3. Basic Metabolic Panel (BMP) / Comprehensive Metabolic Panel (CMP)
| Lab | Normal Range | Critical Values | Key Clinical Notes |
|---|
| Sodium (Na+) | 136–145 mEq/L | <120 or >160 | Hyponatremia: seizures if <120 or rapid drop; correct <8–10 mEq/L per 24h to prevent osmotic demyelination. Hypernatremia: brain shrinkage, lethargy, seizures. Correct slowly. |
| Potassium (K+) | 3.5–5.0 mEq/L | <2.5 or >6.5 | Hypokalemia: muscle weakness, EKG changes (U waves, flat T waves, ST depression); replace PO or IV (max 10–20 mEq/hr IV with cardiac monitoring). Hyperkalemia: peaked T waves → widened QRS → sine wave → VF; causes: renal failure, ACEi, MRA, cell lysis |
| Chloride (Cl-) | 98–106 mEq/L | <80 or >115 | Low: metabolic alkalosis (vomiting), hyperaldosteronism; High: metabolic acidosis (hyperchloremic), NS overuse |
| Bicarbonate (HCO3-) | 22–28 mEq/L | <10 or >40 | Low: metabolic acidosis; High: metabolic alkalosis. Correlates with ABG bicarbonate. |
| BUN (Blood Urea Nitrogen) | 7–20 mg/dL | >100 | High: dehydration, GI bleeding, renal failure, high protein diet, catabolism; BUN/Cr >20:1 = prerenal or upper GI bleed |
| Creatinine (Cr) | 0.6–1.2 mg/dL (varies by age/sex/muscle mass) | >10 (anuria risk) | Best single marker of renal function; a doubling of Cr = ~50% loss of GFR; rises slowly — early AKI may not show for 24–48 hr |
| Glucose | 70–100 mg/dL (fasting); 70–180 mg/dL (ICU) | <40 or >500 | <70 = hypoglycemia; treat <60 aggressively. DKA: usually >250 but can be euglycemic. HHS: >600 with minimal ketones. |
| Calcium (Ca2+) | 8.5–10.5 mg/dL (total); ionized 1.1–1.35 mmol/L | <7 or >13 | Correct for albumin: corrected Ca = measured Ca + 0.8 × (4.0 − albumin). Hypocalcemia: Trousseau, Chvostek, tetany, seizures. Hypercalcemia: "Bones, Groans, Stones, Moans" (bone pain, GI symptoms, kidney stones, psych) |
| Magnesium (Mg2+) | 1.5–2.5 mEq/L | <0.5 or >9 | Hypomagnesemia: refractory hypokalemia and hypocalcemia (must replace Mg first), dysrhythmias, tremors; replace IV or PO. Hypermagnesemia (usually from renal failure or therapeutic): loss of DTRs (first sign) → respiratory depression → cardiac arrest; antidote: calcium gluconate |
| Phosphorus (PO4) | 2.5–4.5 mg/dL | <1.0 or >7 | Hypophosphatemia: refeeding syndrome, DKA recovery, muscle weakness, respiratory failure; replace PO or IV. Hyperphosphatemia: renal failure; binds calcium (hypocalcemia) |
4. Liver Function Tests (LFTs)
| Lab | Normal Range | Clinical Interpretation |
|---|
| ALT (Alanine Aminotransferase) | 7–56 units/L | Liver-specific marker; elevated in hepatocellular injury (viral hepatitis, NASH, drug toxicity); >3× ULN = significant; >10× = acute hepatitis |
| AST (Aspartate Aminotransferase) | 10–40 units/L | Less liver-specific (also in heart, muscle); AST:ALT ratio >2:1 suggests alcoholic liver disease |
| Alkaline Phosphatase (ALP) | 44–147 units/L | Cholestatic/biliary disease; also elevated in bone disease, pregnancy; if elevated with GGT = hepatic origin |
| GGT (Gamma-Glutamyl Transferase) | 0–30 units/L (M); 0–19 (F) | Sensitive marker for alcohol use, biliary disease, drug-induced liver injury; NOT elevated by bone disease (differentiates from ALP) |
| Total Bilirubin | 0.2–1.2 mg/dL | >1.2 = hyperbilirubinemia; >2–3 = jaundice visible. Direct (conjugated): hepatocellular/obstructive. Indirect (unconjugated): hemolysis, Gilbert's syndrome |
| Albumin | 3.5–5.0 g/dL | Marker of chronic liver disease and nutritional status; low = edema (decreased oncotic pressure); affects drug binding and corrected Ca calculation |
| Total Protein | 6.3–8.2 g/dL | Albumin + globulins; low = malnutrition, liver disease, protein-losing enteropathy |
5. Coagulation Studies
| Lab | Normal Range | Critical Value | Notes |
|---|
| PT (Prothrombin Time) | 11–13 seconds | >35 sec | Extrinsic pathway (VII) and common pathway (X, V, II, fibrinogen). Elevated by: warfarin, liver disease, vitamin K deficiency, DIC |
| INR | 0.8–1.2 (non-anticoagulated) | >5 (or >3.5 with symptoms) | Standardized PT ratio. Warfarin target 2–3 (or 2.5–3.5 for mechanical valves). INR >1.5 before invasive procedures |
| aPTT (Activated Partial Thromboplastin Time) | 25–35 seconds | >100 sec | Intrinsic pathway (XII, XI, IX, VIII) and common pathway. Monitored for UFH therapy (therapeutic: 60–100 sec) |
| Fibrinogen | 150–400 mg/dL | <100 mg/dL | Low in DIC (consumed), severe liver failure; replace with cryoprecipitate |
| D-dimer | <0.5 mcg/mL (or institution-specific) | N/A (not a critical value) | High sensitivity for VTE — useful to RULE OUT PE/DVT if low. Not specific — elevated in: infection, pregnancy, surgery, cancer, age >50 |
6. Cardiac Markers
| Lab | Normal | Rise | Peak | Normalization |
|---|
| Troponin I (hsTnI) | <0.04 ng/mL (lab-specific) | 1–6 hr | 12–24 hr | 5–10 days |
| Troponin T (hsTnT) | <0.01 ng/mL | 1–6 hr | 12–24 hr | Up to 14 days |
| CK-MB | <6 ng/mL (or <5% of total CK) | 4–8 hr | 18–24 hr | 36–48 hr |
| BNP | <100 pg/mL | With HF/pressure overload | Variable | With treatment |
| NT-proBNP | Age-adjusted (see HF guide) | With HF | Variable | With treatment |
7. Arterial Blood Gas (ABG)
| Parameter | Normal Range | Notes |
|---|
| pH | 7.35–7.45 | <7.35 = acidosis; >7.45 = alkalosis; critical: <7.20 or >7.60 |
| PaCO2 | 35–45 mmHg | High = hypoventilation (respiratory acidosis); Low = hyperventilation (respiratory alkalosis) |
| PaO2 | 80–100 mmHg | <60 = hypoxemia = respiratory failure; <80 at room air = impaired oxygenation |
| HCO3- | 22–26 mEq/L | Low = metabolic acidosis; High = metabolic alkalosis |
| SaO2 | 95–100% | Oxygen saturation in arterial blood; critical <90% |
| Base Excess/Deficit | -2 to +2 mEq/L | Metabolic component; <-2 = base deficit (metabolic acidosis); >+2 = base excess (metabolic alkalosis) |
4-Step ABG Interpretation
- Is pH acidosis or alkalosis?
- Is the primary disorder respiratory (look at PaCO2) or metabolic (look at HCO3)?
- Is there compensation? (Respiratory: quick; Metabolic: slower, days)
- Assess oxygenation: PaO2 and SaO2
ROME mnemonic: Respiratory Opposite, Metabolic Equal
In respiratory acidosis: pH↓, CO2↑ (OPPOSITE directions). In metabolic acidosis: pH↓, HCO3↓ (EQUAL direction).
8. Urinalysis (UA)
| Component | Normal | Abnormal Finding/Meaning |
|---|
| Color | Pale yellow to amber | Dark yellow/orange: concentrated/dehydration; pink/red: hematuria or myoglobinuria (rhabdo); brown: bilirubin (liver disease) or myoglobinuria; white/cloudy: pyuria (UTI) |
| Specific gravity | 1.003–1.030 | <1.005 = dilute (DI, overhydration); >1.030 = concentrated (dehydration) |
| pH | 4.5–8.0 | Acidic in infection with Staphylococcus; alkaline in Proteus UTI (urea splitter) |
| Protein | None to trace | >300 mg/day = significant proteinuria; nephrotic syndrome; preeclampsia; UTI |
| Glucose | None | Glycosuria: blood glucose >~180 mg/dL (renal threshold); SGLT2 inhibitors cause glycosuria at normal BG |
| Ketones | None | DKA, starvation, prolonged fasting, low-carb diet |
| WBCs (pyuria) | <5 WBCs/HPF | >5 = pyuria → UTI or kidney infection. Sterile pyuria: TB, interstitial nephritis |
| RBCs (hematuria) | <3 RBCs/HPF | Gross or microscopic hematuria: UTI, kidney stones, trauma, bladder cancer, anticoagulation |
| Bacteria | None | Significant bacteriuria + symptoms = UTI; asymptomatic bacteriuria = do NOT treat (except pregnancy) |
| Casts | Hyaline casts only (up to 0–5/LPF) | RBC casts = glomerulonephritis (hallmark); WBC casts = pyelonephritis; granular/muddy brown casts = ATN (AKI) |
9. Critical Values — Call the Provider Immediately
These laboratory values require IMMEDIATE notification of the ordering provider:
- Potassium: <2.5 mEq/L or >6.5 mEq/L
- Sodium: <120 mEq/L or >160 mEq/L
- Glucose: <40 mg/dL or >500 mg/dL
- Calcium: <7 mg/dL or >13 mg/dL (ionized <0.78 or >1.58 mmol/L)
- Magnesium: <0.5 mEq/L or >9 mEq/L
- Hemoglobin: <7 g/dL or >20 g/dL
- Platelets: <50,000/mcL
- WBC: <2,000/mcL or >30,000/mcL
- PT/INR: PT >35 sec or INR >5
- aPTT: >100 sec
- pH: <7.20 or >7.60
- PaO2: <50 mmHg
- Creatinine: >10 mg/dL (acute/new elevation)
- Troponin: Any significant elevation in right clinical context
Document: time value noted, time provider notified, name of provider, what was reported, provider response/orders received.
NCLEX High-Yield Lab Values Points
- Normal K+: 3.5–5.0 mEq/L; Hypokalemia EKG: U waves, flat T; Hyperkalemia EKG: peaked T waves first
- Normal Na+: 136–145 mEq/L; correct hyponatremia ≤8–10 mEq/day (osmotic demyelination risk)
- Correct Ca2+ for albumin: measured Ca + 0.8 × (4.0 − albumin)
- Normal INR: 0.8–1.2; warfarin goal 2–3; mechanical valve 2.5–3.5
- aPTT monitors UFH; INR monitors warfarin; anti-Xa monitors LMWH
- ABG pH <7.35 = acidosis; >7.45 = alkalosis; ROME = Respiratory Opposite, Metabolic Equal
- RBC casts in urine = glomerulonephritis; muddy brown casts = ATN (AKI)
- D-dimer: high sensitivity → rules OUT PE/DVT when low; not specific (many causes of elevation)
- Troponin rises at 3–6 hr, peaks 12–24 hr; stays elevated 5–14 days
- Critical K+: <2.5 (low) or >6.5 (high) → immediate provider notification
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