What are the common causes of an abnormal platelet count (thrombocytosis or thrombocytopenia) in a 21‑year‑old Black female?

Causes of Abnormal Platelet Count in a 21-Year-Old Black Female

In a 21-year-old Black woman with an abnormal platelet count, the most common causes are primary immune thrombocytopenia (ITP) following viral infection if the count is low, or reactive thrombocytosis secondary to infection, inflammation, or iron deficiency if the count is elevated. 1

Initial Critical Step: Confirm True Thrombocytopenia

Before pursuing any workup, you must exclude pseudothrombocytopenia by obtaining a peripheral blood smear reviewed by a hematopathologist, as EDTA-dependent platelet clumping occurs in approximately 0.1% of adults and will falsely lower automated counts. 2, 3 If pseudothrombocytopenia is suspected, redraw blood in a heparin or citrate tube and repeat the platelet count. 4

Common Causes of Thrombocytopenia in This Population

Primary Immune Thrombocytopenia (ITP)

• ITP is the most likely diagnosis in a young, otherwise healthy woman with isolated thrombocytopenia, particularly if preceded by a viral illness. 1, 5 In young adults, ITP typically presents with insidious onset and follows a chronic course, unlike the acute self-limited pattern seen in children. 1

Mandatory Infectious Disease Screening

• Test for HIV and hepatitis C virus in every adult with suspected ITP, regardless of perceived risk factors, as these infections can be clinically indistinguishable from primary ITP and may precede other manifestations by years. 1, 5 HIV-associated thrombocytopenia is particularly common and may be the presenting feature. 2
• Consider H. pylori testing, as eradication therapy can normalize platelet counts in 40-60% of infected ITP patients. 1

Drug-Induced Thrombocytopenia

• Obtain a comprehensive medication history including prescription drugs, over-the-counter medications, herbal supplements, and quinine-containing beverages. 2, 3 Common culprits include sulfonamides, quinidine, heparin, and alcohol. 2

Ethnicity-Specific Considerations

• African-American women may have physiologically lower baseline platelet counts, and a threshold of <125,000/μL (rather than <150,000/μL) may be more appropriate for defining clinically significant thrombocytopenia in this population. 6 This ethnic variation must be considered before labeling a mildly reduced count as pathologic.

Common Causes of Thrombocytosis in This Population

Reactive (Secondary) Thrombocytosis

• Reactive thrombocytosis is far more common than primary thrombocythemia in young adults and rarely causes vascular complications. 7, 8 Common triggers include:
  • Acute or chronic infection 7
  • Iron deficiency anemia (particularly relevant in menstruating women) 1
  • Inflammatory conditions 7
  • Tissue damage or recent surgery 9

Essential Thrombocythemia (Primary)

• Essential thrombocythemia is a myeloproliferative neoplasm that is rare in patients under 40 years but must be excluded if the platelet count exceeds 450,000/μL persistently. 8, 9 Diagnosis requires bone marrow biopsy and detection of JAK2, MPL, or CALR mutations. 9

Diagnostic Algorithm

Step 1: Verify the Abnormality

• Repeat CBC with peripheral smear reviewed by a hematopathologist to exclude pseudothrombocytopenia and identify platelet size, red cell morphology, and white cell abnormalities. 1, 5

Step 2: Determine Isolated vs. Multi-Lineage Involvement

• If anemia or leukopenia coexist with thrombocytopenia, bone marrow examination is mandatory to exclude myelodysplastic syndrome, leukemia, or aplastic anemia. 1, 5

Step 3: Physical Examination Red Flags

• The presence of splenomegaly, hepatomegaly, or lymphadenopathy excludes primary ITP and mandates evaluation for HIV, systemic lupus erythematosus, lymphoproliferative disorders, or chronic liver disease. 2, 1

Step 4: Mandatory Laboratory Testing for Thrombocytopenia

• HIV antibody 1, 5
• Hepatitis C virus antibody 1, 5
• H. pylori testing (urea breath test or stool antigen preferred over serology) 1
• Pregnancy test in women of childbearing age to exclude gestational thrombocytopenia, preeclampsia, or HELLP syndrome 1

Step 5: When to Perform Bone Marrow Examination

• Bone marrow examination is NOT routinely required in young patients with typical ITP features (isolated thrombocytopenia, normal physical exam, no systemic symptoms). 1, 5
• Bone marrow IS mandatory if:
  • Age ≥60 years 1
  • Systemic symptoms (fever, weight loss, bone pain) 1
  • Abnormal CBC beyond isolated thrombocytopenia 1
  • Atypical smear findings (schistocytes, giant platelets, immature cells) 1
  • Splenomegaly or lymphadenopathy 1

Critical Pitfalls to Avoid

• Never diagnose ITP without personal review of the peripheral blood smear, as automated counters miss pseudothrombocytopenia, giant platelets (suggesting inherited thrombocytopenia), and schistocytes (suggesting thrombotic microangiopathy). 1
• Never omit HIV and HCV testing in adults, even in patients without traditional risk factors, as these infections can masquerade as primary ITP for years. 1, 5
• Do not overlook inherited thrombocytopenias such as MYH9-related disease or Bernard-Soulier syndrome, which present with giant platelets on smear and may have a family history. 1
• Missing thrombotic microangiopathy (TTP/HUS) or heparin-induced thrombocytopenia carries catastrophic mortality risk; if schistocytes are present or the patient has received heparin within 3 months, urgent specialized testing is required. 1, 4

Bleeding Risk Stratification

• Platelet counts >50,000/μL: Generally asymptomatic, no activity restrictions needed 4
• Platelet counts 20,000-50,000/μL: Mild skin manifestations (petechiae, purpura); avoid contact sports and antiplatelet medications 2, 4
• Platelet counts <10,000/μL: High risk of serious bleeding; hospitalization and treatment indicated 2, 4