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Hussnain Javaid: MCQ – Based on the Recent BSH’s Guideline on TTP Diagnosis
Hussnain Javaid/LinkedIn
Sep 9, 2026, 12:59

Hussnain Javaid: MCQ – Based on the Recent BSH’s Guideline on TTP Diagnosis

Hussnain Javaid, Consultant Haematologist at NHS UK, Founder of ClinHaem, shared a post on LinkedIn:

“MCQ – Based on the recent BSH’s guideline on TTP diagnosis (released 16/Aug/26)

A 67-year-old man with metastatic gastric adenocarcinoma presents with worsening fatigue and bruising.

His blood results show:

  • Hb 71 g/L
  • Platelets 38 × 10⁹/L
  • Reticulocytes 165 × 10⁹/L
  • LDH 3,850 U/L (120–250 U/L)
  • Blood film: schistocytes present
  • DAT negative
  • Creatinine 156 μmol/L
  • PT 16.8 s (11–14 s)
  • APTT 38 s (25–35 s)
  • D-dimer 8,400 ng/mL FEU (less than 500 ng/mL FEU)
  • ADAMTS13 activity 6 IU/dL (HemosIL CLEIA assay)

He has recently developed rapidly progressive metastatic disease with extensive bone and bone-marrow involvement.

Which one of the following statements is most accurate?

  1. Start caplacizumab
  2. Commence urgent plasma exchange and rituximab.
  3. ADAMTS13 activity less than 20 IU/dL equals near 100% confirmation of iTTP
  4. Send for alternative ADAMTS13 activity testing.
  5. Schistocytes must always be seen in TTP

The correct answer is indeed D: Send for alternative ADAMTS13 activity testing. i.e. via another assay eg FRET or ELISA

Explanation:

The patient clear has MAHA and thrombocytopenia, but has a strong alternative explanation to TTP: rapidly progressive metastatic gastric cancer with marrow involvement and abnormal coagulation markers.

An ADAMTS13 activity of 6 IU/dL would usually strongly support TTP. However, HemosIL CLEIA assay can occasionally give spuriously low ADAMTS13 results (less than 10 IU/dL) when other assays give values above this threshold. In a clinically discordant case, confirmation using an alternative assay is therefore most appropriate.

A quick guide to ADAMTS13 Assays:

All ADAMTS13 activity assays assess the ability of the patient’s ADAMTS13 to cleave a VWF-derived substrate, and they differ in how this cleavage is detected.

  1. FRET (VWF73-FRET): A VWF73 peptide is labelled with fluorescent molecules. Cleavage by ADAMTS13 generates a fluorescent signal, which is proportional to ADAMTS13 activity. This is a manual functional assay.
  2. ELISA: ADAMTS13 cleaves a VWF-derived substrate and the resulting cleavage product is detected using an antibody-based enzyme immunoassay. This is also generally a manual method.
  3. CLEIA (e.g. HemosIL AcuStar): An automated chemiluminescent immunoassay in which ADAMTS13-mediated substrate cleavage ultimately generates a light signal. Its major advantage is rapid, automated testing

Important caveats for ADAMTS13 activity assays:

  1. As you know most guidelines would take ADAMTS13 activity levels of less than 10iu/dl as diagnostic of TTP. Sensitivity or specificity of approximately 97%/100% using ADAMTS13 activity less than 10 IU/dL for confirmation of TTP were established from studies using the manual VWF73-FRET assay.
  2. ⁠For manual FRET and ELISA, ADAMTS13 activity of 10–20 IU/dL is considered a diagnostic grey zone as levels in this range can also be consistent with TTP. (The updated guideline algorithm gives a pathway to navigate this). A comparable grey zone has not yet been established for automated assays.
  3. The current HemosIL CLEIA has also been reported to occasionally produce spuriously low results (less than 10 IU/dL) when alternative assays give results more than 10 IU/dL.

Bottom line: Always interpret ADAMTS13 activity in the context of the assay used and the clinical presentation, rather than relying on the numerical result alone.”

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ADAMTS13 aPTT Blood BSH cancer Caplacizumab Creatinine D dimer DAT ELISA FRET gastric cancer Hb Health Hematology Hemostasis Hemostasis News Hemostasis Today Hussnain Javaid LDH MAHA Medicine platelets PT Reticulocytes Schistocytes thrombocytopenia TTP VWF
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