🩸 Thrombocytopenia

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 🩸 Thrombocytopenia

🔹 Definition

Thrombocytopenia is defined as a platelet count below the normal range (<150,000/mm³).

It is most commonly caused by either:

  1. Impaired platelet production in the bone marrow

  2. Increased platelet destruction or turnover in the periphery

It may also result from redistribution, dilution, or laboratory artifact (pseudothrombocytopenia).

🔹 Etiology

1. Impaired Platelet Production (Bone Marrow Causes)

Mechanism: ↓ megakaryocytes → ↓ thrombopoiesis

Common causes:

Category Examples
Bone marrow failure Aplastic anemia, paroxysmal nocturnal hemoglobinuria
Bone marrow suppression Drugs (linezolid, daptomycin, valproic acid, valacyclovir), chemotherapy, radiation
Congenital / hereditary thrombocytopenias Wiskott-Aldrich syndrome, Alport syndrome, Bernard-Soulier syndrome, Fanconi anemia, von Willebrand disease, Gaucher disease
Infections CMV, EBV, HIV, hepatitis C, parvovirus B19, dengue, mumps, rubella, rickettsia, VZV
Malignancy / infiltration Leukemia, lymphoma, myelodysplastic syndromes, bone marrow infiltration by metastatic tumors
Nutritional deficiency Vitamin B12 and folate deficiency (e.g., chronic alcohol abuse)
Other Necrotizing enterocolitis (in neonates)

Key point: Bone marrow biopsy in impaired platelet production typically shows reduced megakaryocytes.

2. Increased Peripheral Platelet Turnover / Destruction

Mechanism: accelerated consumption or immune-mediated destruction → thrombocytopenia

Causes include:

Category Examples
Autoimmune Immune thrombocytopenia (ITP), SLE, RA
Thrombotic microangiopathies Thrombotic thrombocytopenic purpura (TTP), hemolytic uremic syndrome (HUS)
Consumptive coagulopathy Disseminated intravascular coagulation (DIC), sepsis
Drug-induced immune thrombocytopenia (DITP) Quinine, quinidine, valproate, carbamazepine, amlodipine, linezolid, vancomycin, TMP-SMX, penicillin, ceftriaxone, rifampin, ganciclovir, protease inhibitors, zidovudine, abciximab, heparin, oxaliplatin, suramin, ibuprofen, mirtazapine
Pregnancy-related HELLP syndrome, preeclampsia
Mechanical destruction Artificial cardiac valves, extracorporeal circulation (dialysis)
Post-transfusion Post-transfusion thrombocytopenia

Key point: Bone marrow in these conditions often shows increased megakaryocytes due to compensatory response.

3. Redistribution / Dilutional Causes

  • Liver disease / chronic alcohol use → decreased thrombopoietin

  • Splenomegaly → platelet sequestration

  • Gestational thrombocytopenia → usually mild, second half of pregnancy

  • Transfusion / fluid resuscitation → dilutional effect

  • Pulmonary embolism / pulmonary hypertension → rare redistribution

🔹 Clinical Features

Symptoms are usually correlated with platelet count:

Platelet count Clinical features
>70,000/mm³ Usually asymptomatic
20,000–70,000/mm³ Prolonged bleeding after trauma or surgery, easy bruising, occasional petechiae/purpura
<20,000/mm³ Spontaneous bruising, petechiae, mucosal bleeding (gums, epistaxis), high risk of life-threatening hemorrhage

Other features:

  • Patients with multisystem disease (TTP, DIC, sepsis, liver disease) may have systemic signs: fever, neurological symptoms, renal impairment, jaundice, organomegaly.

🔹 Diagnosis

1. Confirm thrombocytopenia

  • Repeat CBC to confirm persistent thrombocytopenia

  • Check peripheral smear to rule out pseudothrombocytopenia (platelet clumping artifact)

2. Laboratory evaluation

  • CBC with differential → assess for pancytopenia

  • Peripheral blood smear → platelet morphology, schistocytes (TTP/HUS), abnormal WBCs

  • Coagulation studies → bleeding time, PT/PTT (especially in DIC)

  • Renal and liver function tests

  • Other tests → LDH, bilirubin, haptoglobin, urinalysis depending on suspected etiology

3. Etiology-specific workup

Suspected cause Supporting features Diagnostic tests
Infections Fever, travel, vector exposure Serology, PCR, blood cultures
Autoimmune Rash, arthralgia, known autoimmune disease ANA, antiphospholipid antibodies
HIT Recent heparin exposure PF4 antibodies, functional platelet assays
HELLP Pregnancy, abnormal LFTs, ↑LDH, proteinuria Liver panel, CBC, urinalysis
Malignancy B-symptoms, age >60, abnormal smear Bone marrow biopsy, imaging (CT chest/abdomen/pelvis)
Thrombotic microangiopathy Neurologic symptoms, purpura, GI illness Peripheral smear (schistocytes), LDH, bilirubin, renal function, urine protein
Liver disease / hypersplenism Chronic liver disease stigmata, hepatosplenomegaly LFTs, abdominal US, TPO levels

4. Special Considerations

  • Gestational thrombocytopenia → mild (100–150k), benign, usually does not require treatment

  • Pseudothrombocytopenia → falsely low count due to EDTA-induced clumping or lab artifact

  • Dilutional thrombocytopenia → typically after transfusion or fluid resuscitation, affects other cell lines

🔹 Management

Management depends on severity, symptoms, and underlying etiology.

1. All patients

  • Treat active bleeding

  • Address underlying cause

  • Stop medications that impair platelet function (NSAIDs, antiplatelets)

2. Asymptomatic or mild thrombocytopenia

  • Platelet count >50,000/mm³ → monitor, repeat CBC in 1–4 weeks

  • Platelet count <50,000/mm³ but stable → hematology consult

3. Suspected Immune Thrombocytopenia (ITP)

  • Platelet count <30,000/mm³ → consider:

    • Corticosteroids (prednisone, dexamethasone)

    • IVIG (for rapid response or bleeding)

    • Splenectomy (refractory cases)

4. Emergency management

Indications:

  • Neurological symptoms

  • Active, significant bleeding

  • Urgent surgery/invasive procedures

Treatment:

  • Hemostatic control

  • Immediate platelet transfusion (1 unit IV; repeat as needed)

  • If immune-mediated: administer IVIG prior to transfusion

Note: Do not delay treatment for diagnostic testing in cases of life-threatening bleeding or neurological compromise.

🔹 Summary Table: Clinical Approach

Step Action
Confirm Repeat CBC, smear to rule out pseudothrombocytopenia
Assess severity Platelet count, bleeding risk, systemic symptoms
Identify etiology History, meds, infection, autoimmune disease, pregnancy, liver disease
Immediate treatment Active bleeding → platelet transfusion, IVIG if immune cause suspected
Specific treatment ITP → steroids, IVIG, splenectomy; TTP/HUS → plasma exchange; DIC → treat underlying cause
Follow-up Stable, asymptomatic → repeat CBC and monitoring

🔹 Key Points / High-Yield Facts

  • Platelet count <20,000/mm³ → high risk spontaneous bleeding

  • Peripheral smear is crucial to exclude pseudothrombocytopenia or microangiopathic processes

  • Bone marrow biopsy differentiates production vs destruction causes

  • Drugs are a common reversible cause of thrombocytopenia

  • Gestational thrombocytopenia is usually benign, mild, and requires no intervention

  • Severe or symptomatic thrombocytopenia → emergency platelet transfusion and targeted therapy

🔹 References

  1. Hoffman R et al., Hematology: Basic Principles and Practice, 7th ed.

  2. McCrae KR, Platelet Disorders, NEJM 2021

  3. George JN, Immune Thrombocytopenia, NEJM 2000

  4. Kaushansky K, Thrombopoiesis and Platelet Physiology, Blood 2016

  5. AABB Guidelines, Platelet Transfusion, 2025


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