Factor IX assay
Quick answer: This test measures the activity of factor IX, a clotting protein that is low in haemophilia B. It is ordered for unexplained bleeding or a long APTT, to diagnose haemophilia B, and to check carriers.
- SampleBlood
- TakesAbout 5 minutes
- Before the testNo special preparation is usually needed; tell staff about any blood thinners or factor treatment you have had.
- In fertility careWomen who carry haemophilia may be tested before or during pregnancy to plan a safe delivery.
How the test is done
- 1Blood is drawn into a citrate tube filled to the line
- 2The tube is gently mixed
- 3The lab mixes your plasma with plasma that lacks factor IX
- 4The clotting time gives your factor IX activity
What your results can mean
Reading your report
Results are given as a percentage of normal activity; discuss them with your doctor.
If the result is outside the usual range
A low level can point to haemophilia B, carrier status, liver disease or vitamin K deficiency. High levels are not usually a concern.
Who usually has this test
People with a long APTT or a bleeding history, and relatives of people with haemophilia B.
Risks and aftercare
Bruising is possible; press firmly on the site if you have a bleeding tendency.
Names and options
Also called: factor 9 assay, FIX, haemophilia B test
Listed by the hospital as
- FACTOR IX ASSAY, PLASMA
Questions about this test
What is the difference between haemophilia A and B?
Haemophilia A is a lack of factor VIII and haemophilia B is a lack of factor IX. Symptoms are similar, so a factor test tells them apart.
Can newborns be tested for factor IX?
Yes, but newborns naturally have lower factor IX. Results are compared with ranges for their age.
Is haemophilia B inherited?
It is usually passed on through the X chromosome. It mainly affects males, while females are often carriers.
Related tests
Tamara Hospital & IVF Centre, Rajajinagar
34/3, 10th Cross Road, opp. Vardhaka Sardar Patel School, 1st N Block, 2nd Stage, Rajajinagar, Bengaluru 560010
The hospital is open 24 hours. Call before you come to check the timing for your scan or sample collection.
Get directions ↗IVF Pulse fertility care at Tamara Hospital →
Reception
Waiting area
IVF lab
This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.