Initial Bloodwork for Pediatric Petechiae

Core Laboratory Evaluation

The American Society of Hematology recommends a complete blood count (CBC) with differential and peripheral blood smear review as the essential initial bloodwork for a pediatric patient presenting with petechiae, to identify isolated thrombocytopenia versus other cytopenias and evaluate hemoglobin, white blood cell count, and platelet count 1, 2, 3
A complete blood count (CBC) with differential is a fundamental test that evaluates hemoglobin, white blood cell count, and platelet count, and is critical for assessing platelet size and confirming true thrombocytopenia 1, 2, 4
Peripheral blood smear examination is critical for assessing platelet size, confirming true thrombocytopenia, evaluating red and white cell morphology, and identifying schistocytes 1, 4

The presence of fever, bone or joint pain, family history of thrombocytopenia or easy bruising, lymphadenopathy or hepatosplenomegaly, abnormal hemoglobin level, white blood cell count, or white cell morphology, non-petechial rash, or skeletal or soft-tissue morphologic abnormalities requires additional testing beyond CBC and smear 1, 3, 4
The American Society of Hematology specifically recommends against routine testing for antiplatelet antibodies, antiphospholipid antibodies, antinuclear antibodies, thrombopoietin levels, or platelet parameters from automated analyzers in children with suspected immune thrombocytopenia (ITP) 1, 2

For multisystem inflammatory syndrome in children (MIS-C) evaluation, tier 1 testing includes CBC, comprehensive metabolic panel (CMP), ESR, CRP, and SARS-CoV-2 PCR and/or serologies, with tier 2 testing if platelet count <150,000/µL, absolute lymphocyte count <1,000/µL, or sodium <135 mmol/L 7

The American Society of Hematology recommends not delaying diagnosis waiting for antibody testing, as ITP is a clinical diagnosis based on history, examination, CBC, and smear 1, 2
Bone marrow examination is not necessary in children with typical features of ITP, according to the American Society of Hematology, as a retrospective study of 332 children with typical ITP features found no cases of acute leukemia and only one case of bone marrow aplasia 1, 5, 6
Broad-spectrum antibiotics (penicillins, cephalosporins, aminoglycosides) are ineffective against rickettsial diseases, and Rocky Mountain spotted fever should be considered throughout the contiguous United States, not just endemic regions 8