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Test Code F8AS or LAB306 Factor VIII Assay, Plasma

Important Note

If the patient's hematocrit is > 55%, please call the lab to obtain a special blue top with an adjusted level of anticoagulant.

Specimen Requirements

Specimen Type:

Whole Blood

Container Type:

One Blue top: 2.7 mL or 1.8 mL

Optimal Collection Volume:
  • 2.7 mL in solid blue top tube or 1.8 mL in clear blue top tube.  The correct fill volume is indicated by the etched line on the tube.
  • Click here to view the specimen collection guide for blue top (citrate) tubes.

Collection Instructions:
  1. Do not draw from an arm with a heparin lock.
  2. If collected through a blood collection set (butterfly), a discard tube must first be drawn to eliminate dead space from tubing.
  3. Gently invert 5 to 10 times to mix blood.

Specimen Transport Temperature:
  • Room temperature. If testing is delayed, separate plasma and freeze (see outpatient collection instructions below).
  • Specimens cannot be refrigerated

Processing Instructions:
  1. Sample must be centrifuged within one hour of collection.
  2. If testing will be performed > 4 hours from collection time, sample should be processed to obtain platelet-poor plasma, aliquoted, and frozen (see below for processing instructions).

Outpatient collections

  1. Spin down the sample, remove plasma, and spin plasma again to obtain platelet-poor plasma.
  2. Separate the platelet-poor plasma into a screw-top vial.
  3. Freeze plasma immediately.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Specimen Stability

Specimen Type

Temperature

Time

Whole blood

Room Temperature

4 hours

Platelet poor plasma

Room Temperature

4 hours

Platelet poor plasma

Frozen at -20 C

2 weeks

Specimen Rejection Criteria

  • Tube underfilled
  • Refrigerated specimen
  • Clotted specimen

Useful For

  • Diagnosing hemophilia A
  • Diagnosing von Willebrand disease when measured with the von Willebrand factor (vWF) antigen and VWF activity
  • Diagnosing acquired deficiency states
  • investigation of prolonged activated partial thromboplastin time
  • monitoring infusions of factor VIII replacement during interventional procedures and prophylactic infusions.

This test is not useful for inferring carrier status in suspected female carriers of hemophilia A unless it is 50% of normal (<28% activity in adults).

Methodology

The factor VIII assay is performed on the Instrumentation Laboratory ACL Top using the activated partial thromboplastin time (APTT)_ method and a factor-deficient substrate. Patient plasma is combined and incubated with a factor VIII-deficient substrate (normal plasma depleted of factor VIII by immunoadsorption) and an APTT reagent. After a specified incubation time, calcium is added to trigger the coagulation process in the mixture. Then, the time to clot formation is measured optically at a wavelength of 671 nm. 

 

(Owen CA Jr, Bowie EJW, Thompson JH Jr: Diagnosis of Bleeding Disorders. Second edition. Little, Brown and Company, 1975; Meijer P, Verbruggen, Spannagi M: Chapter 33: Clotting factors and inhibitors: Assays and Interpretation. In Laboratory Hematology Practice. Edited by K Kottke-Marchant. Wiley Blackwell Publishing, 2012, pp 435-446)

Reference Ranges

50-200%

Day(s) Performed

Routine testing

  • Available on Monday, Wednesday, and Friday; performed on day shift

STAT testing

  • Available 24/7

Expected TAT

Same day to 3 days

Performing Laboratory

Bronson Laboratory, Coagulation - Kalamazoo

Sample Retention Time

24 hours

CPT Code

85240

LOINC Code

3209-4

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