A 28-year-old primigravida at 32 weeks develops severe pre-eclampsia with headache, visual blurring, BP 168/112 mmHg, proteinuria 3+, and platelet count 95,000/µL. She is started on magnesium sulfate and labetalol. Six hours later, her ALT is 180 U/L, AST 210 U/L, LDH 920 U/L, and she develops right upper quadrant pain. Which of the following haematological parameters most reliably distinguishes HELLP syndrome from thrombotic thrombocytopenic purpura (TTP) in this setting?

• A Platelet count nadir below 50,000/µL
• B Presence of schistocytes on peripheral smear
• C Elevated LDH and low haptoglobin
• D ADAMTS13 activity less than 10% of normal ✓

Explanation

ADAMTS13 (a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13) activity less than 10% is diagnostic of TTP — in HELLP syndrome, ADAMTS13 activity is normal or only mildly reduced (>10%). Both HELLP and TTP present with thrombocytopenia, microangiopathic haemolytic anaemia (schistocytes), and elevated LDH, making these features non-discriminatory. Platelet nadir and LDH elevation occur in both conditions. This distinction is clinically critical because TTP mandates plasma exchange, whereas HELLP requires delivery.

Reference: Williams Obstetrics, 26th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.