HELLP Syndrome: Hemolysis, Elevated Liver Enzymes, and the Falling Platelet Count

What HELLP Is and Why It Matters

HELLP syndrome is a thrombotic microangiopathy of pregnancy and is best understood as a severe end of the preeclampsia spectrum rather than a wholly separate disease. The acronym, coined by Louis Weinstein in 1982, names its defining laboratory triad: Hemolysis (intravascular red-cell destruction), Elevated Liver enzymes, and Low Platelets.

It matters because it is both common enough to be seen regularly and lethal enough to demand urgent action. HELLP complicates about 0.5-0.9% of pregnancies and 10-20% of severe preeclampsia. Maternal mortality runs roughly 1%, but morbidity is high: DIC (~20%), abruptio placentae, acute kidney injury, pulmonary edema, and hepatic hematoma.

• Up to 15-20% of patients are normotensive or lack proteinuria at presentation — the classic 'atypical' HELLP that fools clinicians.
• Roughly 30% of cases present postpartum, usually within 48 hours of delivery.

The Mechanism, Step by Step

HELLP shares its origin with preeclampsia: defective placentation. In early pregnancy, extravillous trophoblasts fail to remodel the maternal spiral arteries into low-resistance vessels, leaving the placenta chronically underperfused and ischemic.

• Angiogenic imbalance: the ischemic placenta releases anti-angiogenic factors — soluble fms-like tyrosine kinase-1 (sFlt-1), a decoy receptor that sequesters VEGF and PlGF, plus soluble endoglin (sEng), which blocks TGF-β signaling. Loss of VEGF/PlGF tone strips the endothelium of its survival signals.
• Endothelial injury: damaged endothelium and exposed subendothelial collagen trigger platelet activation and consumption (thrombocytopenia) and lay down fibrin microthrombi.
• Microangiopathic hemolysis: red cells are sheared as they force through fibrin-narrowed microvessels, generating schistocytes, releasing LDH and free hemoglobin, and consuming haptoglobin.
• Hepatic injury: periportal fibrin deposition and sinusoidal obstruction cause hepatocyte necrosis (rising AST/ALT) and can distend Glisson's capsule.

Uncontrolled alternative-complement activation amplifies the whole cascade, placing HELLP mechanistically alongside the complement-mediated microangiopathies.

Clinical Presentation and Classic Signs

The presentation is often deceptively vague, which is precisely the trap. The most common and characteristic complaint is right-upper-quadrant or epigastric pain (present in ~90%), from hepatic capsular stretch — frequently mistaken for reflux, gallbladder disease, or 'the flu.'

• Constitutional symptoms: malaise (up to 90%), nausea and vomiting (~50%), a general sense of being unwell days before diagnosis.
• Preeclampsia features when present: hypertension (~85%) and proteinuria (~85%) — but remember a meaningful minority lack these.
• Red-flag symptoms of severe/impending catastrophe: severe headache, visual disturbance, and shoulder-tip pain or sudden shock — the latter suggesting subcapsular liver hematoma rupture with hemoperitoneum.

On exam look for RUQ tenderness, hyperreflexia and clonus (neurologic irritability presaging eclampsia), edema, and jaundice in advanced hemolysis. Because symptoms peak in the third trimester and can debut postpartum, any peripartum woman with epigastric pain deserves a HELLP screen.

Diagnosis: The Specific Tests, Criteria, and Cutoffs

HELLP is a laboratory diagnosis. The most widely used framework is the Tennessee (Sibai) complete criteria, requiring all three: hemolysis (peripheral smear with schistocytes, LDH >600 U/L, or total bilirubin ≥1.2 mg/dL and low haptoglobin), AST ≥70 U/L, and platelets <100 ×10⁹/L. Meeting only one or two defines partial/incomplete HELLP, which still requires vigilance.

• Mississippi (Martin) system grades severity by platelet nadir — Class I ≤50, Class II 50-100, Class III 100-150 ×10⁹/L — and predicts maternal morbidity; Class I carries the highest risk.
• Confirmatory hemolysis labs: undetectable haptoglobin is highly specific; a rising indirect bilirubin and reticulocytosis support it.
• Coagulation: check PT/aPTT/fibrinogen and D-dimer to catch DIC.
• Imaging: RUQ ultrasound or CT/MRI if hepatic hematoma, infarction, or rupture is suspected.

An adjunct sFlt-1/PlGF ratio can support the placental etiology — a ratio ≤38 has a ~99% negative predictive value for preeclampsia within one week (PROGNOSIS study).

Management at a Mechanism Level and Key Complications

Because the disease is driven by the placenta, delivery is the only definitive cure — it removes the source of sFlt-1/sEng, allowing endothelium to recover. Timing balances maternal risk against fetal maturity:

• ≥34 weeks, or maternal/fetal instability, DIC, or hepatic rupture: deliver promptly after stabilization.
• <34 weeks and stable: a brief 24-48 h delay for antenatal corticosteroids (betamethasone) to accelerate fetal lung maturity may be reasonable.

Supportive pillars target the downstream physiology:

• Magnesium sulfate for seizure (eclampsia) prophylaxis — a 4-6 g load then 1-2 g/hr, continued 24 h postpartum. Mg competes at neuronal calcium channels and NMDA receptors to raise the seizure threshold.
• Antihypertensives (IV labetalol, hydralazine, or oral nifedipine) for BP ≥160/110 to prevent maternal stroke.
• Transfusion of platelets/FFP/cryoprecipitate for active bleeding, severe thrombocytopenia before surgery, or DIC.

Do-not-miss complications: subcapsular liver hematoma (<2%, rupture mortality 18-86%), DIC, abruption, AKI, and pulmonary edema. High-dose corticosteroids do not improve maternal outcomes and are not recommended solely to raise platelets.

Mimics, Pitfalls, and Clinical Significance

HELLP's greatest danger is misdiagnosis, because several conditions share the microangiopathic-thrombocytopenia picture. Distinguishing them changes treatment: HELLP resolves with delivery, whereas TTP needs plasma exchange and aHUS needs complement blockade (eculizumab).

• Acute fatty liver of pregnancy (AFLP): more marked hypoglycemia, hyperammonemia, elevated INR/coagulopathy out of proportion, and less thrombocytopenia; Swansea criteria help.
• TTP: pentad with prominent neurologic signs, near-normal liver enzymes, and severely low ADAMTS13 activity (<10%).
• aHUS: AKI dominates, often postpartum, driven by alternative-complement dysregulation.
• Other mimics: antiphospholipid syndrome, SLE flare, viral hepatitis, and DIC from sepsis.

Key pitfalls: anchoring on 'gastritis' in a woman with epigastric pain; dismissing HELLP because BP is normal; and forgetting the postpartum window. Counsel patients that HELLP recurs in ~2-19% of future pregnancies and confers long-term cardiovascular and hypertensive risk — making it a lifelong health signal, not just an obstetric event.

HELLP diagnostic criteria and severity classification (Tennessee complete criteria vs. Mississippi triple-class system)

Class / System	Platelet count	AST (or AST/ALT)	LDH
Tennessee (complete HELLP)	<100 ×10⁹/L	AST ≥70 U/L	≥600 U/L (with hemolysis on smear / low haptoglobin)
Mississippi Class I (severe)	≤50 ×10⁹/L	AST ≥70 U/L	≥600 U/L
Mississippi Class II (moderate)	50-100 ×10⁹/L	AST ≥70 U/L	≥600 U/L
Mississippi Class III (mild)	100-150 ×10⁹/L	AST ≥40 U/L	≥600 U/L
Partial / incomplete HELLP	Only 1-2 of the 3 criteria met — still warrants close monitoring, can progress	—	—