Question regarding LMW Heparin - USMLE Forums
USMLE Forums Logo
USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
USMLE Articles
Go Back   USMLE Forums > USMLE Step 1 Forum

USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam

Thread Tools Search this Thread Display Modes
Old 11-06-2009
USMLE Forums Veteran
Steps History: ---
Posts: 238
Threads: 56
Thanked 197 Times in 60 Posts
Reputation: 227
Blood Question regarding LMW Heparin

I faced this question on USMLERx stating that LMW Heparin acts primarily on AT III whereas unfractionated heparin targets both factors Xa and IIa.

Is that correct? Why is it that FA pg 341 mention that LMW Heparin act more on Xa then?
Reply With Quote Quick reply to this message

Old 11-06-2009
USMLE Forums Master
Steps History: 1+CK+CS+3
Posts: 3,318
Threads: 170
Thanked 4,844 Times in 1,808 Posts
Reputation: 4897

To inhibit Thrombin (factor IIa) the heparin molecule has to bind to Anti-Thrombin III and Thrombin simultaneously.
The binding to to ATIII is via a high affinity penta-saccharide sequence while the binding to Thrombin is via additional 13 saccharides.

To inhibit factor Xa the heparin molecule need only the pentasaccharide sequence and no need for binding the Xa molecule.

Therefore, heparin molecules (less than 18 saccharides in length) i.e. LMW heparin will act more by inhibiting factor Xa than on thrombin (IIa).

Have a look at this illustration
Question regarding LMW Heparin-atiii.jpg
click to enlarge

Image Referenced from <a href="">10.1378/chest.119.1_suppl.64S <cite> <abbr title="CHEST" class="slug-jnl-abbrev"> CHEST</abbr> January 2001 vol. 119 no. 1 suppl 64S-94S </cite>
Reply With Quote Quick reply to this message
The above post was thanked by:
smile135 (11-08-2009), tima (11-07-2009)


Figures-, Hematology-, Pharmacology-

Quick Reply

Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

Favorite USMLE Books
What USMLE books you really think are useful. Leave blank if you don't want to tell.
Where you live. Leave blank if you don't want to tell.


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Similar Threads
Thread Thread Starter Forum Replies Last Post
question help: diabetic foot related question dezirablize USMLE Step 2 CK Forum 5 01-15-2015 02:42 PM
How Warfarin can cause hypercoagulation if given without Heparin? donofitaly USMLE Step 1 Forum 4 12-04-2010 02:12 AM

RSS Feed
Find Us on Facebook
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.

USMLE® & other trade marks belong to their respective owners, read full disclaimer
USMLE Forums created under Creative Commons 3.0 License. (2009-2014)