Factor Inhibitor Screen (Blood)

Testing Laboratory

Auckland Te Toka Tumai | Auckland Hospital

Department

Haematology

Delphic Registration Code (Alpha Code)

CMSC

Test Code (Numeric Code)

1850

Laboratory Handling

Phlebotomy

Collect 1 x 2.7ml Citrate (Blue Cap) or 1 x 1.8ml Citrate (Light Blue Cap).

Tube must be adequately filled.

Transport

Do not place on 8100.

Frozen samples are stored in the Specimen Services Freezer (No 35) in the Coagulation rack.

Partially thawed samples should be given directly to the Coagulation staff.

Registration

Please register test code CMSC.

Sample Stability

24-hours

Synonyms

Factor IX Inhibitor Screen
Factor VIII Inhibitor Screen

Turnaround Time

2 weeks

Specimens assayed fortnightly.

Specimen Type

• Whole Blood

Specimen Requirements

Tube/Container Type:

Preferred

• Please refer to Additional Information below
• Citrate (Blue Cap)

Acceptable

• Please refer to Additional Information below
• Citrate (Light Blue Cap)

Preferred Sample Volume (ml)

2.7

Minimum Sample Volume (ml)

2.7

No of Samples Required

1

Paediatric Specimen Requirements

Tube/Container Type:

Preferred

• Please refer to Additional Information below
• Citrate (Blue Cap)

Pre-testing Requirements

Please arrange with the Technical Specialist in the Coagulation laboratory (Ext 22069), Haematology Registrar or Haematologist.

Additional Specimen Information

Collect 1 x 2.7ml Citrate (Blue Cap) or 1 x 1.8ml Citrate (Light Blue Cap).
Tube must be adequately filled.

Test Method

A factor inhibitor screen (or incubated APTT mixing study) identifies time- and temperature-dependent coagulation inhibitors, such as acquired Factor VIII antibodies. The test mixes patient plasma with normal pooled plasma, incubates it at 37°C, and measures clotting times (aPTT) at 0 and 120 minutes to see if the inhibitor progressively destroys factor activity.
A factor inhibitor screen for non-VIII factors like Factor IX (FIX) uses a modified mixing study based on the activated partial thromboplastin time (aPTT). It measures residual factor activity after incubating a 1:1 mix of patient plasma and normal pooled plasma at 37°C for one hour to detect time-dependent inhibitors. The residual factor activity of the mixture is compared to a control mix (normal plasma incubated alongside). Recovery significantly lower than expected indicates a positive inhibitor screen.

Contact Information