Dr Abdul Mannan Comments Raheel Moazzam’s Thesis: Why are Left-Sided DVTs More Common Than Right?
Dr Abdul Mannan, Consultant Haematologist at Betsi Cadwaladr University Health Board, shared a post on LinkedIn:
“Why are left-sided DVTs more common than right?
We’ve known this pattern for decades. But the reason wasn’t clear.
Until now.
Dr Raheel Moazzam ‘s thesis at Imperial College London answers this question. Her work discovered something we didn’t know before: the left common iliac vein (LCIV) is anatomically narrower than the right. Not because of compression. Not because of disease. Just normal human anatomy.
This is a genuine anatomical finding.
Here’s why it matters:
- Narrower vein = slower blood flow (Poiseuille’s Law)
- Slower flow = baseline venous stasis
- Stasis is one leg of Virchow’s Triad
- The LCIV sits in a state of “primed risk.” Like a loaded gun.
But stasis alone doesn’t cause clots. You need triggers:
- Hypercoagulability (genetics, hormones)
- Immobility (flights, surgery, bed rest)
- Dehydration (increased blood viscosity)
When these hit someone with a narrow LCIV, they cross the thrombosis threshold. That’s the multi-hit hypothesis.
Someone with a wide vein tolerates these triggers. Someone with a narrow vein doesn’t.
This explains the left-right difference we see in clinical practice.
I’ve created a visual to summarise this concept for teaching. Credit goes to Dr Moazzam for this elegant piece of work connecting anatomy to clinical reality.
What do you think? Does this change how you explain DVT risk to patients?”

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