Neonatal Thrombocytopenia

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Definition And Baseline Values

Thrombocytopenia in neonates is defined as a platelet count less than 150,000 per cubic millimeter.
The mean platelet count is greater than or equal to 200,000 per cubic millimeter in most preterm infants.
The fifth centile may be as low as 104,000 per cubic millimeter for neonates born at 32 weeks of gestation or less.
The fifth centile is 123,000 per cubic millimeter for late preterm and term neonates.
Regardless of gestation, a platelet count of less than 100,000 per cubic millimeter mandates a thorough clinical evaluation.

Etiological Classification

Disorders of primary hemostasis are predominantly caused by abnormalities in the number or function of platelets.
The causes of low platelets are broadly classified into increased destruction and decreased production.

Increased Destruction Of Platelets

Mechanism

Common Causes

Nonimmune Destruction

Infections: Gram-negative sepsis (Klebsiella, Acinetobacter). Fungal sepsis (Invasive candidiasis). Viral infections (Cytomegalovirus, Rubella, Herpes simplex virus, Enterovirus, Dengue, Chikungunya). Systemic Illness: Necrotizing enterocolitis (NEC), severe birth asphyxia, disseminated intravascular coagulation (DIC). Vascular/Sequestration: Hemangioma (Kasabach-Merritt syndrome), Hypersplenism. Iatrogenic/Microangiopathic: Massive transfusion, extracorporeal membrane oxygenation (ECMO), Thrombotic thrombocytopenic purpura (TTP), Neonatal hemolytic-uremic syndrome (HUS).

Immune Destruction

Fetal and neonatal alloimmune thrombocytopenia (FNAIT). Mother with Idiopathic thrombocytopenic purpura (ITP) or systemic lupus erythematosus.

Decreased Production Of Platelets

Mechanism	Common Causes
Maternal Factors	Pregnancy-induced hypertension (PIH), Fetal growth restriction (FGR), Polycythemia. Low platelets occur due to cell line steal, where bone marrow redirects production to red blood cells.
Bone Marrow Infiltration	Osteopetrosis, Congenital leukemia, Hemophagocytic lymphohistiocytosis (HLH).
Bone Marrow Failure	Congenital amegakaryocytic thrombocytopenia, Thrombocytopenia absent radius (TAR) syndrome.

Platelet Function Disorders

Adhesion defects: Bernard-Soulier syndrome, von Willebrand disease.
Aggregation defects: Glanzmann's thrombasthenia.
Cytoskeleton defects: Wiskott-Aldrich syndrome, MYH9-related disorders.

Clinical Presentation

Neonates with platelet disorders typically present with petechiae, small mucosal bleeds, and ecchymosis.
Immune thrombocytopenia can manifest with mild bleeding that resolves within a week.
Severe cases can present with intracranial hemorrhage (ICH) leading to death or severe neurodevelopmental sequelae.
Untreated immune cases have a 10% to 20% risk of developing ICH.

Fetal And Neonatal Alloimmune Thrombocytopenia (FNAIT)

FNAIT is the most common cause of severe, life-threatening thrombocytopenia in neonates.
The mother lacks a specific human platelet antigen (commonly HPA 1a or HPA 5b) that the fetus possesses.
Maternal antibodies cross the placenta and destroy the fetal platelets.
The mother is completely asymptomatic and has a normal platelet count.
The clinical presentation in the neonate is highly variable.
It ranges from asymptomatic thrombocytopenia to major organ bleeds, transient hematuria, bloody stools, and ICH.

Diagnostic Approach

First-Line Investigations

A complete blood count with a platelet count is the primary investigation.
A peripheral blood smear is crucial to evaluate the differential diagnosis.
In a peripheral smear, 1 platelet per oil immersion field corresponds to a count of 10,000 to 15,000 per cubic millimeter.
Giant platelets on the smear indicate hyperutilization or increased destruction.
Fragmented red blood cells or schistocytes (greater than 10%) strongly suggest DIC.
Prothrombin time, activated partial thromboplastin time, and fibrinogen levels should be checked to rule out consumptive coagulopathies like DIC.

Specific Diagnostic Tests

Human Platelet Antigen (HPA) Analysis: This is indicated if FNAIT is suspected. It tests for the presence of maternal antiplatelet antibodies directed against fetal antigens.
Cranial Ultrasound: An urgent cranial ultrasound is mandatory to rule out intracranial bleeding in any neonate with a platelet count less than 50,000 per cubic millimeter.

Management Strategies

Platelet Transfusion Guidelines

Platelet transfusions are indicated based on strict threshold guidelines and the clinical condition of the neonate.
Random donor platelets are typically used; single donor platelets are reserved for expected prolonged severe thrombocytopenia.
High-risk neonates have favorable outcomes when restrictive thresholds are utilized.

Target Platelet Count	Clinical Indication
< 25,000 / mm³	Asymptomatic neonates with no active bleeding. Neonates with NAIT if there is no bleeding and no family history of ICH.
< 50,000 / mm³	Neonates with active bleeding. Neonates with current coagulopathy. Prior to any surgical procedure. Neonates with NAIT if a previously affected sibling had an ICH.
< 100,000 / mm³	Major life-threatening bleeding (e.g., significant intraventricular hemorrhage). Prior to major surgery. Neonates with NAIT who have developed an ICH.

Transfusion Administration And Practical Tips

The recommended volume for a platelet transfusion is 10 to 20 mL/kg.
The recommended rate of administration is 10 to 20 mL/kg/hour.
A 10 mL/kg dose can increase the platelet count by approximately 100,000 per liter.
Platelet components must be irradiated and leuko-reduced to prevent transfusion-associated graft-versus-host disease and cytomegalovirus transmission.
Group O platelets should be avoided for non-O patients whenever possible.

Management Of Fetal And Neonatal Alloimmune Thrombocytopenia (FNAIT)

Washed maternal platelets or platelets from an antigen-negative donor are the ideal treatment.
If antigen-negative platelets are unavailable, random donor platelets must be transfused immediately in emergencies.
Intravenous immunoglobulin (IVIG) is administered concurrently at a dose of 1 g/kg/day for 2 days.
If the platelet count is less than 25,000 per cubic millimeter, use random donor platelets and IVIG.
If the platelet count is between 25,000 and 50,000 per cubic millimeter, IVIG alone is indicated.
In neonates with active bleeding or ICH, the target platelet count must be kept at 100,000 per cubic millimeter.
Following stabilization, the count should be maintained at 50,000 per cubic millimeter for 7 days.

Management Of Autoimmune Thrombocytopenia (Maternal ITP)

Perform a platelet count on day one from the cord blood.
If the count is normal, repeat it on day three.
If the count is between 100,000 and 150,000 per cubic millimeter, repeat it between days 3 and 5 of life.
If the count drops below 100,000 per cubic millimeter, monitor daily.
Unlike FNAIT, random donor platelets are rapidly destroyed by circulating maternal antibodies.
Platelet transfusions serve only as a temporary measure in autoimmune etiologies.
IVIG remains the definitive treatment of choice and rapidly raises the platelet count.