Nursing lab values cheat sheet: normal ranges and clinical significance

Lab values are the language of clinical nursing. Every morning assessment, every provider call, every charting entry is built around numbers — and knowing which numbers matter, what they mean, and when to act is a core nursing competency from day one.

This cheat sheet covers the most commonly ordered lab panels in adult inpatient and outpatient settings. Each section includes a reference table with normal ranges and units, followed by explanations of clinical significance and nursing priorities. For a full listing of the abbreviations used throughout — CBC, BMP, ABG, and others — see the nursing abbreviations reference tool.

Use this as a study guide, a quick bedside reference, and an NCLEX review tool. Values here reflect standard adult reference ranges; always confirm against your facility’s laboratory-specific reference intervals, which may vary slightly by analyzer and population.

CBC: complete blood count

The CBC is one of the most frequently ordered lab panels in nursing. It gives a snapshot of red blood cell function, oxygen-carrying capacity, immune status, and clotting potential.

WBC: what high and low values mean

An elevated WBC (leukocytosis) most often signals infection, inflammation, or physiologic stress. Sepsis, pneumonia, appendicitis, and steroid use can all drive the count up. A critically high WBC (>30 × 10³/μL) may indicate leukemia or severe sepsis.

A low WBC (leukopenia, <4.5 × 10³/μL) signals immunosuppression — common after chemotherapy, in bone marrow disorders, or with certain medications (methotrexate, clozapine). Patients with a neutrophil count below 1.0 × 10³/μL are considered neutropenic and require protective isolation precautions.

Nursing action: Report WBC outside reference range to the provider, especially if fever, infection signs, or active chemotherapy are present. A critical WBC (>30 or <2.0 × 10³/μL) requires immediate notification.

Hemoglobin and hematocrit

Hemoglobin (Hgb) and hematocrit (Hct) move together — the Hct is roughly three times the Hgb value. Both are used to assess anemia and bleeding.

Anemia thresholds for transfusion consideration vary, but most facilities use Hgb <7–8 g/dL as a trigger in stable patients. Symptoms of anemia — fatigue, pallor, dyspnea on exertion, tachycardia — often precede lab threshold crossings.

A high hemoglobin and hematocrit (polycythemia) can result from dehydration (hemoconcentration), chronic hypoxia (COPD, altitude), or polycythemia vera. Dehydration is the most common cause on an inpatient unit.

Nursing action: Assess for signs of active bleeding with any acute drop. Check volume status before attributing a high Hct to polycythemia.

MCV: classifying anemia

MCV tells you the size of red blood cells and helps identify the cause of anemia:

• Microcytic (MCV <80 fL): Iron deficiency anemia, thalassemia, chronic disease anemia
• Normocytic (MCV 80–100 fL): Acute blood loss, hemolytic anemia, early combined deficiency
• Macrocytic (MCV >100 fL): B12 or folate deficiency, liver disease, hypothyroidism, alcohol use

Platelets

Low platelets (thrombocytopenia, <150 × 10³/μL) increase bleeding risk. Critical threshold is typically <50 × 10³/μL for procedures and <20 × 10³/μL for spontaneous hemorrhage risk. Common causes include ITP, heparin-induced thrombocytopenia (HIT), DIC, and bone marrow suppression.

High platelets (thrombocytosis, >400 × 10³/μL) can indicate reactive thrombocytosis (infection, inflammation, iron deficiency) or, rarely, a myeloproliferative disorder.

Nursing action: Apply pressure to all venipuncture sites in thrombocytopenic patients. Report platelets <100 × 10³/μL in patients scheduled for invasive procedures.

BMP/CMP: metabolic panels

The basic metabolic panel (BMP) and comprehensive metabolic panel (CMP) assess electrolyte balance, kidney function, blood sugar, and — in the CMP — liver function. For a deeper look at what happens when these electrolytes are out of balance, see the guide to electrolyte imbalances in nursing.

Electrolytes and kidney function

Sodium is the primary extracellular cation and the key driver of plasma osmolality. Hyponatremia (<136 mEq/L) causes cellular swelling — neurological symptoms range from headache and confusion to seizures. Hypernatremia (>145 mEq/L) causes cellular dehydration, presenting as lethargy, irritability, and thirst.

Potassium is critical for cardiac conduction. Both hypokalemia (<3.5 mEq/L) and hyperkalemia (>5.0 mEq/L) can cause life-threatening dysrhythmias. Always check the EKG in patients with potassium outside the normal range. See the EKG interpretation cheat sheet for the characteristic changes associated with potassium imbalances (peaked T waves in hyperkalemia; U waves and flat T waves in hypokalemia).

BUN and creatinine are both markers of kidney function, but they behave differently. Creatinine is a more reliable indicator of glomerular filtration rate (GFR) because it is produced at a relatively constant rate by muscle metabolism and is filtered without reabsorption. BUN can be elevated by factors unrelated to kidney function — high protein intake, GI bleeding, dehydration, and catabolic states all raise BUN without affecting creatinine proportionally. See the Common Confusions section below for more on the BUN:creatinine ratio.

Glucose

Fasting glucose 70–100 mg/dL is normal. Pre-diabetes is 100–125 mg/dL. Diabetes is diagnosed at ≥126 mg/dL on two separate occasions, or ≥200 mg/dL with symptoms. In hospitalized patients, blood glucose is often targeted at 140–180 mg/dL, balancing glycemic control against hypoglycemia risk.

Nursing action: Critical glucose thresholds typically trigger immediate intervention — hypoglycemia (<70 mg/dL) requires prompt glucose administration; severe hyperglycemia (>400–500 mg/dL) requires provider notification and assessment for DKA or HHS.

Additional electrolytes

Calcium and phosphorus have an inverse relationship — as one rises, the other tends to fall. This relationship is regulated by parathyroid hormone (PTH) and vitamin D. Low calcium (hypocalcemia) manifests as neuromuscular irritability — Chvostek’s sign (facial twitch on tapping the facial nerve) and Trousseau’s sign (carpal spasm with blood pressure cuff inflation) are classic clinical findings.

Liver function tests (CMP)

ALT is more liver-specific than AST — when ALT is markedly elevated, the liver is the primary source. AST is also found in cardiac and skeletal muscle, so it can rise in myocardial infarction or rhabdomyolysis. An AST:ALT ratio >2:1 is suggestive of alcoholic liver disease.

Albumin reflects both nutritional status and liver synthetic function. A low albumin (<3.5 g/dL) is seen in malnutrition, liver failure, nephrotic syndrome, and chronic inflammatory states. It also affects drug distribution — many medications are albumin-bound, so low albumin increases free drug levels and risk of toxicity.

ABG: arterial blood gas

Arterial blood gas values assess oxygenation and acid-base status. ABG interpretation is essential for managing respiratory failure, metabolic emergencies, and mechanical ventilation.

The ROME mnemonic for ABG interpretation

A reliable memory tool for ABG interpretation is ROME:

• Respiratory Opposite: in respiratory disorders, pH and PaCO₂ move in opposite directions (pH↓ with PaCO₂↑ = respiratory acidosis; pH↑ with PaCO₂↓ = respiratory alkalosis)
• Metabolic Equal: in metabolic disorders, pH and HCO₃⁻ move in the same direction (pH↓ with HCO₃⁻↓ = metabolic acidosis; pH↑ with HCO₃⁻↑ = metabolic alkalosis)

Four primary acid-base disorders

PaO₂ and oxygenation

PaO₂ reflects dissolved oxygen in arterial blood. A PaO₂ of 80–100 mmHg is normal at sea level on room air. Hypoxemia is defined as PaO₂ <80 mmHg. SaO₂ (pulse oximetry equivalent: SpO₂) reflects hemoglobin oxygen saturation — target SpO₂ ≥95% in most patients, with some COPD patients intentionally maintained at 88–92% to preserve their hypoxic drive.

Coagulation studies

Coagulation panels assess the clotting cascade and are essential for monitoring anticoagulation therapy.

PT and INR

PT measures the extrinsic and common coagulation pathways and is primarily used to monitor warfarin therapy. Because PT values vary by laboratory reagent, INR was developed to standardize reporting. For patients on warfarin for atrial fibrillation or VTE, a therapeutic INR is typically 2.0–3.0. For mechanical heart valves, the target is often higher (2.5–3.5). An INR >4.0 carries significant bleeding risk and warrants provider notification.

aPTT and heparin

aPTT measures the intrinsic and common pathways and is used to monitor unfractionated heparin (UFH) therapy. A therapeutic aPTT for heparin is typically 60–100 seconds (1.5–2.5 times the normal range), though this varies by facility protocol. Low-molecular-weight heparins (enoxaparin, dalteparin) do not require routine aPTT monitoring.

Fibrinogen and DIC

A falling fibrinogen (below 200 mg/dL) combined with elevated PT, aPTT, and low platelets is the classic pattern of disseminated intravascular coagulation (DIC) — a life-threatening consumptive coagulopathy. Report all critical coagulation values immediately.

Thyroid and cardiac markers

Thyroid function

TSH is the first-line test for thyroid function. An elevated TSH (>4.0 mIU/L) suggests hypothyroidism — the pituitary is working harder to stimulate an underactive thyroid. A suppressed TSH (<0.4 mIU/L) suggests hyperthyroidism. Free T4 is measured alongside TSH to confirm and grade the disorder.

Cardiac markers

Troponin I is the most sensitive and specific marker for myocardial injury. Any value above 0.04 ng/mL in the appropriate clinical context (chest pain, EKG changes) is considered elevated until proven otherwise. Serial troponin measurements (at 0, 3, and 6 hours) are used to identify rising or falling patterns characteristic of acute MI. A delta troponin (rising value) is more diagnostic than a single elevated reading.

BNP is released by ventricular cardiomyocytes in response to stretch and volume overload. Values >100 pg/mL support a diagnosis of heart failure; values >400 pg/mL indicate moderate-to-severe heart failure. BNP is also useful for distinguishing cardiac from pulmonary causes of dyspnea. See the EKG interpretation cheat sheet for the cardiac rhythm findings that accompany these clinical states.

Clinical applications: using lab values in practice

Morning assessment

Most inpatient facilities report overnight labs before the morning shift. The morning lab review is a structured part of the nursing assessment:

1. Compare today’s values to yesterday’s — trending matters as much as a single result
2. Flag any values outside normal range and cross-reference with the patient’s condition and current medications
3. Note critical values (those reported by the lab immediately) — these require immediate provider notification and documentation of the notification time
4. Anticipate orders: low potassium may prompt a replacement order; elevated creatinine may trigger a nephrology consult or medication dose adjustment

Notifying providers

When calling a provider about an abnormal lab value, use SBAR communication to structure the report: Situation (which value, how abnormal), Background (relevant history, current medications), Assessment (your clinical interpretation), Recommendation (what you think is needed). Document the call, the provider’s name, time of notification, and any orders received.

Critical values — those outside ranges defined as immediately life-threatening — require notification within minutes. Each facility sets its own critical value thresholds, but common examples include: potassium <2.5 or >6.5 mEq/L, sodium <120 or >160 mEq/L, glucose <40 or >500 mg/dL, pH <7.20 or >7.60, platelet count <20 × 10³/μL.

Charting lab values

Document abnormal findings in your nursing note, your response, and the provider notification. For critical values, include the exact time the lab was reported, the time you notified the provider, the provider’s response, and any nursing interventions initiated. When reviewing medications, cross-check dosing against renal function (creatinine clearance) and coagulation status — many medications require dose adjustment or hold decisions based on lab results. See the overview of medication rights in nursing for the broader framework of safe medication administration.

Common confusions

BUN vs. creatinine: which is the better kidney marker?

Both rise in kidney dysfunction, but creatinine is more specific. BUN is elevated by anything that increases protein catabolism — GI bleeding, high protein intake, steroids, dehydration — regardless of kidney function. The BUN:creatinine ratio can help interpret results: a ratio >20:1 in the setting of normal creatinine suggests a prerenal cause (dehydration, GI bleed) rather than intrinsic renal failure. A ratio 10–20:1 is typical with true renal impairment.

PT vs. aPTT: which pathway are you testing?

PT (and INR) tests the extrinsic pathway — affected by warfarin and vitamin K deficiency. aPTT tests the intrinsic pathway — affected by heparin and factor deficiencies (hemophilia A and B). In DIC, both are prolonged because the common pathway is consumed. Remembering “warfarin = PT, heparin = aPTT” covers the majority of clinical scenarios.

Hemoglobin vs. hematocrit: reading the trend

Because Hct is approximately three times the Hgb value (a useful bedside estimation), a Hgb of 10 g/dL corresponds to a Hct of roughly 30%. Disproportionate discrepancy between these values — for example, a Hct that is much less than 3× the Hgb — may signal a lab error or an unusual condition (severe microcytosis, lipemia) and warrants repeat testing.

SaO₂ vs. SpO₂

SaO₂ is measured directly from arterial blood (as part of an ABG). SpO₂ is the non-invasive pulse oximetry estimate. They correlate closely in most patients, but SpO₂ overestimates saturation in the presence of carbon monoxide (carboxyhemoglobin), methemoglobinemia, and severe anemia. An ABG is required when clinical presentation does not match the SpO₂ reading.

Related references

• Electrolyte imbalances nursing mnemonics — signs, symptoms, and mnemonics for sodium, potassium, calcium, and magnesium imbalances
• EKG interpretation cheat sheet — normal intervals, waveform analysis, and common rhythm patterns
• Nursing abbreviations reference tool — searchable database of 500+ nursing abbreviations
• SBAR communication — structured handoff communication for provider notification
• Nursing cheat sheet library — all cheat sheets, mnemonics, and reference guides in one place