Nonblanching rash is not a single diagnosis — it is a finding that demands immediate assessment. The blanch test takes seconds and changes the entire clinical approach. The differential ranges from benign mechanical petechiae to immediately life-threatening meningococcemia, TTP, and vasculitis.
CLINICAL PRINTABLE
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1 · Recognition
- Petechiae: pinpoint (< 2 mm), flat, nonblanching red or purple spots caused by extravasation of red blood cells into the dermis. Do not blanch with pressure. Caused by thrombocytopenia, platelet dysfunction, increased intravascular pressure, or vasculitis.
- Purpura: larger (2 mm – 1 cm) nonblanching red-purple lesions. Palpable purpura (raised) indicates vasculitis — immune complex deposition in vessel walls. Non-palpable purpura indicates thrombocytopenia or coagulopathy.
- Ecchymosis: bruising — larger areas of purpura from blunt trauma or coagulopathy. Petechiae and purpura are not bruises — they are caused by different mechanisms.
- The blanch test: press firmly with a glass or finger. Blanching (color disappears) = vascular dilation (inflammatory, reactive). Nonblanching = extravasated red blood cells in the dermis. Nonblanching rash requires immediate assessment regardless of the patient's apparent stability.
- Distribution matters: petechiae above the nipple line (face, neck, upper chest) after Valsalva (coughing, vomiting, crying) are benign mechanical petechiae. Petechiae below the nipple line, on the lower extremities, or with systemic symptoms require urgent evaluation.
2 · Differential / Common Traps
- Assuming petechiae are benign without checking the platelet count: thrombocytopenic purpura (ITP, TTP, HUS, drug-induced) can present with petechiae and purpura. Always check CBC with platelet count in a patient with nonblanching rash.
- Missing meningococcemia: the petechial/purpuric rash of meningococcemia can initially appear as a few petechiae that rapidly progress to widespread purpura fulminans. Any patient with fever + nonblanching rash + headache or neck stiffness requires immediate evaluation and empiric antibiotics.
- Confusing palpable purpura with non-palpable purpura: palpable purpura (raised, firm) indicates vasculitis — immune complex deposition in vessel walls. Non-palpable purpura is flat and indicates thrombocytopenia or coagulopathy. The distinction changes the differential and workup.
- Missing TTP: thrombotic thrombocytopenic purpura presents with the pentad of thrombocytopenia, microangiopathic hemolytic anemia, neurological symptoms, renal dysfunction, and fever. Not all five features are required. Schistocytes on peripheral smear + thrombocytopenia + elevated LDH should prompt urgent hematology consultation.
- Attributing petechiae to trauma without adequate workup: while traumatic petechiae exist, petechiae in unusual locations (non-trauma-exposed areas), with systemic symptoms, or in a patient on anticoagulants require platelet count and coagulation studies before attributing to trauma.
3 · Workup and Interpretation
- CBC with differential and platelet count: essential in all patients with nonblanching rash. Thrombocytopenia, leukocytosis, or leukopenia changes the differential immediately.
- Peripheral blood smear: look for schistocytes (TTP/HUS), blast cells (leukemia), or platelet clumping (pseudothrombocytopenia).
- Coagulation studies (PT, PTT, fibrinogen, D-dimer): for suspected DIC, coagulopathy, or anticoagulant effect.
- Blood cultures + LP (if meningococcemia or meningitis is suspected): do not delay empiric antibiotics for LP if the patient is unstable.
- ADAMTS13 activity: for suspected TTP (thrombocytopenia + microangiopathic hemolytic anemia + neurological symptoms). Severely reduced ADAMTS13 activity (< 10%) confirms TTP.
- Skin biopsy: for suspected vasculitis (palpable purpura) — direct immunofluorescence and histopathology identify the type of vasculitis and guide systemic workup.
4 · Treatment / Management
Meningococcemia
Empiric IV antibiotics immediately (ceftriaxone 2 g IV). Do not delay for LP if the patient is unstable. Dexamethasone before or with first antibiotic dose. ICU transfer. Notify public health for contact prophylaxis.
ITP (immune thrombocytopenic purpura)
Platelet count > 30,000 without bleeding: observation may be appropriate. Platelet count < 30,000 or significant bleeding: IVIG, corticosteroids (prednisone), or both. Platelet transfusion for life-threatening bleeding (temporary effect). Hematology consultation.
TTP
Urgent plasma exchange (plasmapheresis) is the definitive treatment — do not delay. Corticosteroids as adjunct. Rituximab for refractory or relapsing TTP. Platelet transfusion is relatively contraindicated (can worsen thrombosis). Hematology consultation is urgent.
IgA vasculitis (Henoch-Schönlein purpura)
Supportive care for mild disease. NSAIDs for arthralgia. Corticosteroids for severe GI involvement or nephritis. Monitor renal function (urinalysis, creatinine) — nephrology consultation for significant renal involvement.
Drug-induced thrombocytopenia
Identify and discontinue the offending drug. Platelet count typically recovers within 5–10 days after drug discontinuation. IVIG or corticosteroids for severe thrombocytopenia with bleeding. Heparin-induced thrombocytopenia (HIT) requires immediate heparin cessation and alternative anticoagulation.
5 · Expected Course / Reassessment
- Mechanical petechiae (Valsalva) resolve within days without treatment.
- ITP: acute ITP in children often resolves spontaneously. Chronic ITP in adults requires ongoing management. Most patients achieve remission with treatment.
- TTP: mortality without treatment approaches 90%. With plasma exchange, survival exceeds 80%. Relapse occurs in approximately 30–40% of cases.
- Meningococcemia: mortality is 10–15% even with treatment. Survivors may have significant sequelae (limb loss from purpura fulminans, hearing loss, neurological deficits).
- IgA vasculitis: most cases in children resolve spontaneously. Renal involvement (IgA nephropathy) can persist and requires long-term monitoring.
6 · Escalation
- Fever + nonblanching rash + headache or neck stiffness — meningococcemia. Empiric IV antibiotics immediately. Do not wait for LP.
- Thrombocytopenia + schistocytes + elevated LDH + neurological symptoms — TTP. Urgent plasma exchange. Hematology consultation immediately.
- Platelet count < 10,000 or active bleeding with thrombocytopenia — urgent hematology consultation, consider platelet transfusion for life-threatening bleeding.
- Purpura fulminans (rapidly spreading purpura with skin necrosis and systemic toxicity) — ICU transfer, empiric antibiotics, hematology/infectious disease consultation.
Apply It · Patient Cases
CASE 1
A 4-year-old presents with petechiae on the face and neck after a prolonged coughing episode. The petechiae are above the nipple line, the child is afebrile, and CBC is normal. Mechanical petechiae from increased intrathoracic pressure during coughing. No treatment required — parents are reassured and instructed to return if new petechiae appear below the nipple line or if fever develops.
CASE 2
A 19-year-old presents with fever, headache, and a rapidly spreading petechial rash on the lower extremities and trunk. He appears ill. Meningococcemia is suspected. Blood cultures are drawn, ceftriaxone 2 g IV is given immediately, and he is transferred to the ICU. LP is deferred until he is stabilized.
NOW CHANGE ONE DETAIL
Same patient as Case 2, but the rash is palpable purpura on the lower extremities, and he has arthralgia and abdominal pain. CBC shows normal platelet count. IgA vasculitis (Henoch-Schönlein purpura) is suspected. Urinalysis shows hematuria. Nephrology is consulted for renal involvement.
Bottom Line
Nonblanching rash demands immediate assessment. Fever + petechiae = meningococcemia until proven otherwise. Palpable purpura = vasculitis. Thrombocytopenia + schistocytes = TTP. The appearance changes the urgency.
EVIDENCE & REFERENCES
- Briere J, et al. Purpura and petechiae. In: UpToDate. Wolters Kluwer; 2024. https://www.uptodate.com
- George JN, Nester CM. Syndromes of thrombotic microangiopathy. N Engl J Med. 2014;371(7):654–666. doi:10.1056/NEJMra1312353
- Jennette JC, Falk RJ. Small-vessel vasculitis. N Engl J Med. 1997;337(21):1512–1523. doi:10.1056/NEJM199711203372106