Unilateral swollen/red/painful leg
A streamlined, differential-led presentation for rapid clinical review.
Twenty-second review
- A unilateral swollen painful leg may reflect venous thrombosis, cellulitis, trauma, ruptured cyst, or impaired lymphatic or venous drainage.
- Dyspnea, pleuritic pain, syncope, shock, threatened limb perfusion, rapidly spreading infection, or severe pain out of proportion is high risk.
- Keep dependent edema or musculoskeletal injury in the differential; overlapping or concurrent illness remains possible.
- For unilateral swollen/red/painful leg, trends and combinations of findings are more informative than one isolated vital sign.
Compare the clinical patterns
The repeated material is grouped inside each possibility. Open only the condition you need.
Pulmonary embolismTime-sensitive high-risk possibility
HPI
Clarify acute vs chronic; unilateral swelling, redness, warmth; calf/thigh pain.
Signs & symptoms
Cardiopulmonary symptoms, neurovascular change, toxicity, or disproportionate pain.
Focused exam
Assess perfusion, bleeding sites, limb symmetry, skin changes, respiratory findings, and neurologic status; Trend pain, swelling, oxygenation, and circulation.
Brief pathophysiology
Pulmonary embolism may cause unilateral swollen/red/painful leg through a time-sensitive process capable of rapid physiological deterioration.
What the trend may show
Pulmonary embolism may have normal observations. Tachycardia, tachypnea, or hypoxemia increase concern; hypotension identifies hemodynamic compromise rather than being required for diagnosis.
Heart rate (bpm)
May riseTachycardia is common but neither sensitive nor specific.
Respiratory rate (breaths/min)
May riseTachypnea may be an early sign of increased ventilatory demand.
Oxygen saturation (SpO₂)
May fallHypoxemia may occur, but a normal saturation does not exclude PE.
Blood pressure (mmHg)
Often preservedHypotension suggests high-risk PE with obstructive shock.
Front-load in the triage report
- Pulmonary embolism: Cardiopulmonary symptoms, neurovascular change, toxicity, or disproportionate pain.
- Acute vs chronic.
- Unilateral swelling, redness, warmth.
Compartment syndromeTime-sensitive high-risk possibility
HPI
Clarify unilateral swelling, redness, warmth; calf/thigh pain; chest pain/dyspnea suggesting pe.
Signs & symptoms
Cardiopulmonary symptoms, neurovascular change, toxicity, or disproportionate pain.
Focused exam
Trend pain, swelling, oxygenation, and circulation; Compare both legs for circumference, warmth, colour, tenderness, edema, wounds, pulses, distal function, and infection signs without forceful massage.
Brief pathophysiology
Compartment syndrome may cause unilateral swollen/red/painful leg through a time-sensitive process capable of rapid physiological deterioration.
What the trend may show
Hematologic differentials may affect oxygen delivery, thrombosis, bleeding, or infection risk. Rate, pressure, oxygenation, and temperature provide the most useful physiologic screen.
Heart rate (bpm)
May riseTachycardia may reflect anemia, pain, bleeding, fever, or hypoxia.
Blood pressure (mmHg)
May fallHypotension suggests significant bleeding, sepsis, or shock.
Oxygen saturation (SpO₂)
Interpret cautiouslySpO₂ measures saturation, not hemoglobin concentration or total oxygen content.
Temperature (°C)
Trend temperatureFever raises concern for infection, especially with immune compromise.
Front-load in the triage report
- Compartment syndrome: Cardiopulmonary symptoms, neurovascular change, toxicity, or disproportionate pain.
- Unilateral swelling, redness, warmth.
- Calf/thigh pain.
Necrotizing infectionTime-sensitive high-risk possibility
HPI
Clarify calf/thigh pain; chest pain/dyspnea suggesting pe; prior dvt/pe.
Signs & symptoms
Cardiopulmonary symptoms, neurovascular change, toxicity, or disproportionate pain.
Focused exam
Trend pain, swelling, oxygenation, and circulation; Compare both legs for circumference, warmth, colour, tenderness, edema, wounds, pulses, distal function, and infection signs without forceful massage.
Brief pathophysiology
Necrotizing infection may cause unilateral swollen/red/painful leg through a time-sensitive process capable of rapid physiological deterioration.
What the trend may show
Hematologic differentials may affect oxygen delivery, thrombosis, bleeding, or infection risk. Rate, pressure, oxygenation, and temperature provide the most useful physiologic screen.
Heart rate (bpm)
May riseTachycardia may reflect anemia, pain, bleeding, fever, or hypoxia.
Blood pressure (mmHg)
May fallHypotension suggests significant bleeding, sepsis, or shock.
Oxygen saturation (SpO₂)
Interpret cautiouslySpO₂ measures saturation, not hemoglobin concentration or total oxygen content.
Temperature (°C)
Trend temperatureFever raises concern for infection, especially with immune compromise.
Front-load in the triage report
- Necrotizing infection: Cardiopulmonary symptoms, neurovascular change, toxicity, or disproportionate pain.
- Calf/thigh pain.
- Chest pain/dyspnea suggesting PE.
DVTCommon presentation pattern
HPI
Clarify acute vs chronic; unilateral swelling, redness, warmth; calf/thigh pain.
Signs & symptoms
Risk factors, tenderness, edema, warmth, erythema, and skin source guide the differential.
Focused exam
Assess perfusion, bleeding sites, limb symmetry, skin changes, respiratory findings, and neurologic status; Trend pain, swelling, oxygenation, and circulation.
Brief pathophysiology
DVT may explain the presenting symptoms through a common clinical mechanism, while serial assessment checks for complications or an alternate cause.
What the trend may show
Pulmonary embolism may have normal observations. Tachycardia, tachypnea, or hypoxemia increase concern; hypotension identifies hemodynamic compromise rather than being required for diagnosis.
Heart rate (bpm)
May riseTachycardia is common but neither sensitive nor specific.
Respiratory rate (breaths/min)
May riseTachypnea may be an early sign of increased ventilatory demand.
Oxygen saturation (SpO₂)
May fallHypoxemia may occur, but a normal saturation does not exclude PE.
Blood pressure (mmHg)
Often preservedHypotension suggests high-risk PE with obstructive shock.
Front-load in the triage report
- Risk factors, tenderness, edema, warmth, erythema, and skin source guide the differential.
- Acute vs chronic.
- Unilateral swelling, redness, warmth.
CellulitisCommon presentation pattern
HPI
Clarify unilateral swelling, redness, warmth; calf/thigh pain; chest pain/dyspnea suggesting pe.
Signs & symptoms
Risk factors, tenderness, edema, warmth, erythema, and skin source guide the differential.
Focused exam
Trend pain, swelling, oxygenation, and circulation; Compare both legs for circumference, warmth, colour, tenderness, edema, wounds, pulses, distal function, and infection signs without forceful massage.
Brief pathophysiology
Cellulitis may explain the presenting symptoms through a common clinical mechanism, while serial assessment checks for complications or an alternate cause.
What the trend may show
Hematologic differentials may affect oxygen delivery, thrombosis, bleeding, or infection risk. Rate, pressure, oxygenation, and temperature provide the most useful physiologic screen.
Heart rate (bpm)
May riseTachycardia may reflect anemia, pain, bleeding, fever, or hypoxia.
Blood pressure (mmHg)
May fallHypotension suggests significant bleeding, sepsis, or shock.
Oxygen saturation (SpO₂)
Interpret cautiouslySpO₂ measures saturation, not hemoglobin concentration or total oxygen content.
Temperature (°C)
Trend temperatureFever raises concern for infection, especially with immune compromise.
Front-load in the triage report
- Risk factors, tenderness, edema, warmth, erythema, and skin source guide the differential.
- Unilateral swelling, redness, warmth.
- Calf/thigh pain.
Dependent edemaImportant alternative presentation
HPI
Clarify acute vs chronic; unilateral swelling, redness, warmth; calf/thigh pain.
Signs & symptoms
Bilateral pattern or clear injury may suggest alternatives.
Focused exam
Assess perfusion, bleeding sites, limb symmetry, skin changes, respiratory findings, and neurologic status; Trend pain, swelling, oxygenation, and circulation.
Brief pathophysiology
Dependent edema can resemble unilateral swollen/red/painful leg through overlapping symptoms or referred physiology despite a different primary mechanism.
What the trend may show
Hematologic differentials may affect oxygen delivery, thrombosis, bleeding, or infection risk. Rate, pressure, oxygenation, and temperature provide the most useful physiologic screen.
Heart rate (bpm)
May riseTachycardia may reflect anemia, pain, bleeding, fever, or hypoxia.
Blood pressure (mmHg)
May fallHypotension suggests significant bleeding, sepsis, or shock.
Oxygen saturation (SpO₂)
Interpret cautiouslySpO₂ measures saturation, not hemoglobin concentration or total oxygen content.
Temperature (°C)
Trend temperatureFever raises concern for infection, especially with immune compromise.
Front-load in the triage report
- Bilateral pattern or clear injury may suggest alternatives.
- Acute vs chronic.
- Unilateral swelling, redness, warmth.
Musculoskeletal injuryImportant alternative presentation
HPI
Clarify unilateral swelling, redness, warmth; calf/thigh pain; chest pain/dyspnea suggesting pe.
Signs & symptoms
Bilateral pattern or clear injury may suggest alternatives.
Focused exam
Trend pain, swelling, oxygenation, and circulation; Compare both legs for circumference, warmth, colour, tenderness, edema, wounds, pulses, distal function, and infection signs without forceful massage.
Brief pathophysiology
Musculoskeletal injury can resemble unilateral swollen/red/painful leg through overlapping symptoms or referred physiology despite a different primary mechanism.
What the trend may show
Isolated musculoskeletal injury often leaves central vital signs near baseline. Persistent abnormality should prompt reassessment for hemorrhage, thoracic injury, infection, or a medical cause.
Heart rate (bpm)
May rise with painTachycardia can reflect pain or distress; trend after treatment.
Blood pressure (mmHg)
May rise with painHypotension is not expected in an isolated minor injury.
Respiratory rate (breaths/min)
May rise with painPersistent tachypnea suggests more than a minor isolated injury.
Oxygen saturation (SpO₂)
Usually preservedDesaturation suggests thoracic injury or concurrent disease.
Front-load in the triage report
- Bilateral pattern or clear injury may suggest alternatives.
- Unilateral swelling, redness, warmth.
- Calf/thigh pain.
Findings that should escalate concern
- Dyspnea, pleuritic pain, syncope, shock, threatened limb perfusion, rapidly spreading infection, or severe pain out of proportion is high risk.
- Pulmonary embolism, compartment syndrome, or necrotizing infection: Cardiopulmonary symptoms, neurovascular change, toxicity, or disproportionate pain.
Medication recognition
Continue the clinical pathway
Clinical and academic sources
Curated clinical guidance and peer-reviewed evidence supporting this presentation. Current BCEHS guidance, medical direction, and local policy remain authoritative for practice.
BCEHS Handbook — specific CPGs
Supporting clinical and academic evidence
- CEDIS Presenting Complaint List updateCanadian Association of Emergency Physicians
Presenting-complaint terminology and categorization context. It does not establish a prehospital “top 100” ranking.
- ASH Clinical Practice GuidelinesAmerican Society of Hematology
Evidence-based guidance covering common hematologic emergencies, thrombosis, bleeding disorders, and sickle cell disease.
- Venous thromboembolismThe Lancet · 2021
DVT and pulmonary embolism risk factors, clinical assessment, diagnosis, and treatment context.