What are the diagnostic criteria for HELLP syndrome (Hemolysis, Elevated Liver enzymes, Low Platelet count)?

HELLP Syndrome Diagnostic Criteria

HELLP syndrome is diagnosed by the presence of three laboratory findings: hemolysis (evidenced by peripheral blood smear showing microangiopathic changes, elevated LDH, or low haptoglobin), elevated liver enzymes (AST ≥70 U/L), and thrombocytopenia (platelets <100,000/mm³). 1

Core Diagnostic Components

The diagnosis requires all three of the following laboratory abnormalities 2:

1. Hemolysis - Evidence includes:

• Microangiopathic hemolytic anemia on peripheral blood smear 1
• Elevated lactate dehydrogenase (LDH) >600 U/L 3
• Elevated indirect bilirubin 2
• Low serum haptoglobin levels 2

2. Elevated Liver Enzymes:

• Aspartate aminotransferase (AST) ≥70 U/L 3
• Alanine aminotransferase (ALT) typically elevated (>45 U/L) 1
• LDH >600 U/L 3

3. Low Platelet Count:

• Platelets <100,000/mm³ (100 × 10⁹/L) 1, 3, 2

Classification Systems

Tennessee Classification System

The most widely used diagnostic criteria require 3:

• Hemolysis with LDH >600 U/L
• AST ≥70 U/L
• Platelets <100 × 10⁹/L

Mississippi Triple-Class System

Further stratifies HELLP syndrome by severity based on platelet nadir 3:

• Class 1: Platelets ≤50,000/mm³
• Class 2: Platelets >50,000 to ≤100,000/mm³
• Class 3: Platelets >100,000 to ≤150,000/mm³

Complete vs. Partial HELLP Syndrome

Complete HELLP syndrome requires all three diagnostic criteria to be met 4. Partial HELLP syndrome is diagnosed when only one or two (but not all three) features are present 4. This distinction is clinically important because complete HELLP syndrome carries significantly higher maternal morbidity, including increased rates of disseminated intravascular coagulation, need for transfusion, and cesarean delivery compared to partial HELLP or severe preeclampsia alone 4.

Clinical Context and Associated Features

Typical Clinical Presentation 1:

• Epigastric or right upper quadrant pain (most common presenting symptom) 5
• Nausea and vomiting 1
• Malaise
• Hypertension (blood pressure typically >160/90 mmHg) 1
• Proteinuria (>5 g/24 hours in severe cases) 1

Important Caveats:

• Blood pressure levels do NOT correlate with disease severity 6. Diagnosis must be based on biochemical laboratory evidence, not blood pressure readings alone 6.
• Approximately 70% of cases develop antepartum (most commonly between 27-37 weeks gestation), while 30% occur within 48 hours postpartum 3
• HELLP syndrome can be misdiagnosed initially as acute cholecystitis, drug reaction, or idiopathic thrombocytopenia 1

Additional Laboratory Findings

Supportive laboratory abnormalities that should be checked 1:

• Elevated fibrin degradation products (>10 µg/L suggests DIC)
• Normal or mildly prolonged PT/PTT (unless DIC develops)
• Normal fibrinogen (unless DIC develops)
• Elevated creatinine, urea, and uric acid (renal involvement)
• Decreased total protein and albumin

Differential Diagnosis Considerations

Rule out other causes of hemolysis and thrombocytopenia before confirming HELLP syndrome 2:

• Acute fatty liver of pregnancy (may have overlapping features) 7
• Thrombotic thrombocytopenic purpura (TTP)
• Hemolytic uremic syndrome (HUS)
• Idiopathic thrombocytopenic purpura (ITP)
• Acute viral hepatitis
• Drug-induced liver injury

ELLP Syndrome Variant

A variant called ELLP syndrome (Elevated Liver enzymes, Low Platelets) has been described in patients with severe preeclampsia who meet criteria for elevated liver enzymes and thrombocytopenia but have no evidence of hemolysis (normal bilirubin, absence of schistocytes, normal reticulocyte count) 8. These patients should be managed similarly to HELLP syndrome but studied separately in research contexts 8.

Key Clinical Pitfalls

• Do not rely on blood pressure alone to assess severity—laboratory values are the definitive diagnostic criteria 6
• Do not delay diagnosis waiting for all three criteria to become severely abnormal—the syndrome is progressive and early recognition is critical 1, 3
• Do not overlook postpartum presentation—30% of cases occur after delivery, so maintain high suspicion in the immediate postpartum period 3
• The degree of thrombocytopenia correlates well with the degree of liver dysfunction and overall disease severity 1