A platelet count of 22 × 10^9/L with schistocytes is not a vocabulary exercise. It is a thrombotic microangiopathy until proven otherwise, and the first clinical question is not simply, “Is this HELLP?” It is: what mechanism is consuming platelets and fragmenting red cells, and will delivery reverse it?
In the teaching case, ADAMTS13 activity of 6%—if the sample was obtained before plasma infusion or plasma exchange—moves thrombotic thrombocytopenic purpura (TTP) to the top of the differential. The AST of 42 U/L, with an upper limit of 35 U/L, is only about 1.2 times normal and does not meet the transaminase threshold used in many complete-HELLP definitions. Creatinine of 124 µmol/L, approximately 1.4 mg/dL, is in the severe-feature range if preeclampsia has otherwise been established and there is no preexisting renal disease, but renal dysfunction does not identify the cause of the thrombotic microangiopathy.
Start with the syndrome, not the label
The shared syndrome is a triad:
- Microangiopathic hemolytic anemia: falling hemoglobin, schistocytes, elevated LDH, low haptoglobin, indirect hyperbilirubinemia, or reticulocytosis
- Thrombocytopenia: platelet consumption in the microvasculature
- End-organ injury: neurologic, renal, hepatic, cardiac, placental, or gastrointestinal involvement
That triad defines a clinical problem, not a diagnosis. HELLP, TTP, complement-mediated thrombotic microangiopathy, severe preeclampsia, disseminated intravascular coagulation, catastrophic antiphospholipid syndrome, infection, and other secondary TMAs can overlap.
Commonly used complete-HELLP criteria require evidence of hemolysis, elevated AST or ALT—often at least twice the upper limit of normal—and platelets below 100 × 10^9/L. Definitions vary, and partial HELLP or preeclampsia with severe features can still be dangerous. HELLP itself may occur without severe-range hypertension, whereas a diagnosis of preeclampsia still requires qualifying hypertension. The practical point is that a very low platelet count plus hemolysis should not be relabeled as HELLP merely because the patient is pregnant.
Before formulating a hypertensive-disease diagnosis, establish the blood-pressure trajectory, baseline creatinine, urine protein assessment, and whether new hypertension is present. Ask about persistent headache, visual symptoms, confusion, seizures, dyspnea, chest pain, right-upper-quadrant or epigastric pain, oliguria, bleeding, and reduced exercise tolerance. Also obtain prior pregnancy history, prior episodes of thrombocytopenia or hemolysis, known TTP or kidney disease, autoimmune disease, family history of TMA, recent infection or diarrhea, medications, transfusion, surgery, hemorrhage, and sepsis risk.
Why TTP can look like severe obstetric disease
TTP results from severe deficiency of ADAMTS13, the protease that cleaves ultra-large von Willebrand factor multimers. When ADAMTS13 activity is profoundly reduced, platelet-rich microthrombi form throughout the circulation, producing marked thrombocytopenia, hemolysis, and ischemic organ injury.
Pregnancy increases von Willebrand factor and changes the hemostatic balance, so it can precipitate either immune-mediated or congenital TTP. Neurologic findings such as headache, confusion, focal deficits, seizures, or fluctuating mental status should increase concern. Renal injury can occur, but very severe thrombocytopenia with comparatively modest kidney impairment is a pattern that favors TTP over complement-mediated TMA.
A pretreatment ADAMTS13 activity below 10% is the characteristic laboratory signal for TTP in a compatible TMA presentation. It should be sent urgently, ideally before plasma transfusion or plasma exchange, because replacement ADAMTS13 can raise the measured activity and obscure the result. A profoundly low result strongly supports TTP, but laboratory values must still be interpreted in clinical context; rare secondary conditions can complicate assay interpretation.
| Feature | HELLP or preeclampsia spectrum | TTP or complement-mediated TMA clues |
|---|---|---|
| Timing | Usually after 20 weeks or around delivery and early postpartum | TTP can occur in any trimester; complement-mediated TMA is often prominent postpartum |
| Dominant pattern | Hemolysis with meaningful liver injury and thrombocytopenia; hypertension may be absent or not severe | TTP: profound thrombocytopenia and neurologic features; aHUS: progressive, often severe kidney injury |
| Key discriminator | Obstetric context and evolution after delivery | TTP: ADAMTS13 activity below 10%; aHUS: persistent TMA with severe renal injury after other causes are excluded |
| Response to delivery | Usually shows a trend toward improvement within 48–72 hours, although early postpartum worsening can occur | TTP and aHUS do not reliably resolve with delivery alone |
These are patterns, not mandatory criteria. For example, TTP can coexist with hypertension, proteinuria, fetal growth restriction, or placental dysfunction. Conversely, HELLP can have substantial renal or neurologic complications. The goal is not to force every patient into one column; it is to identify the treatment that cannot safely wait.
Management is parallel, not sequential
First, stabilize the patient and evaluate both maternal and fetal status. Repeat the CBC and smear; obtain LDH, bilirubin, haptoglobin, reticulocyte count, creatinine, liver enzymes, urinalysis, urine protein assessment, coagulation studies, fibrinogen, and type-and-screen. Evaluate for pulmonary edema, neurologic injury, cardiac ischemia, and reduced urine output. Involve maternal-fetal medicine, hematology, nephrology, critical care, and neonatology early when the presentation is severe.
Second, treat obstetric emergencies without waiting for perfect diagnostic certainty. Acute severe blood pressure requires prompt treatment according to obstetric protocol. Magnesium sulfate may be indicated for seizure prevention in a patient with preeclampsia with severe features; it does not treat TTP. Delivery is definitive treatment for the placenta-driven component of HELLP and is guided by maternal instability, fetal status, gestational age, and the feasibility of safe prolongation.
Third, do not use delivery as a substitute for TTP treatment. If clinical probability of TTP is high—particularly when MAHA and severe thrombocytopenia are accompanied by neurologic features and/or relatively modest renal injury—start urgent hematology-directed plasma exchange and corticosteroids while ADAMTS13 testing is pending. A platelet count near or below 30 × 10^9/L alone is not diagnostic. Additional disease-specific therapy may also be needed. The exact regimen depends on whether the process is immune-mediated or congenital and on pregnancy-specific risk–benefit assessment.
If ADAMTS13 is not severely reduced and kidney injury is progressive—especially after delivery—consider complement-mediated TMA. There is no single confirmatory bedside test for pregnancy-associated aHUS; it is generally a diagnosis of exclusion supported by the clinical course, renal phenotype, and exclusion of TTP and other secondary causes. If complement-mediated TMA remains likely after TTP and other important causes have been evaluated, urgent nephrology and hematology consultation is needed to consider complement inhibition; delivery alone is not adequate treatment. Failure of the platelet count, hemolysis, or creatinine to show a trend toward improvement within 48–72 hours, or progressive renal injury, should trigger that reassessment rather than repeated reassurance that the patient has severe HELLP.
Apply the framework to the teaching case
The platelet count of 22, hemoglobin of 8.2 g/dL, LDH of 1,200 U/L, and numerous schistocytes establish a severe MAHA-thrombocytopenia picture. The mild AST elevation does not fulfill the usual complete-HELLP transaminase threshold. The vignette does not provide blood-pressure, urine-protein, neurologic, or abdominal findings, so it does not permit a complete formulation of the hypertensive disorder; HELLP itself cannot be diagnosed from thrombocytopenia and hemolysis alone.
If ADAMTS13 activity of 6% was measured before plasma therapy, the most important working diagnosis is TTP. Delivery may still be required for maternal or fetal indications, but it should occur alongside—not instead of—urgent TTP-directed therapy.
Practical takeaways
- Treat MAHA plus thrombocytopenia as a thrombotic microangiopathy syndrome before assigning an obstetric label.
- ADAMTS13 activity below 10% strongly supports TTP, especially from a pretreatment sample, but should be interpreted in clinical context.
- Mild transaminitis does not exclude TTP; it may argue against complete HELLP when the usual threshold is not met.
- Severe-feature thresholds describe organ dysfunction, not its cause.
- Delivery treats the placenta-driven component of HELLP but does not reliably treat TTP or aHUS.
- Failure of hemolysis, thrombocytopenia, or kidney injury to show expected improvement within 48–72 hours after delivery—or progressive renal injury—is a diagnostic alarm, not a reason for repeated reassurance.