Lab Dept:


Test Name:


General Information

Lab Order Codes:

F8U (Back-up only)


AHF; AHG; Antihemophiliac Factor; FVIII; VIII:C; Hemophilia A; Factor VIII Assay

CPT Codes:

85240 – Clotting; factor VIII (AHG), one stage

Test Includes:

Factor VIII activity reported as a %.


Test Indications:

Useful for the detection of a single congenital homozygous or heterozygous factor deficiency for Hemophilia A or von Willebrand’s disease or an acquired deficiency due to liver disease or DIC.

Lab Testing Section:

Sendouts - Coagulation

Referred to:

Fairview University Medical Center (Fairview/Atlas test: F8)

Phone Numbers:

MIN Lab: 612-813-6280

STP Lab: 651-220-6550

Test Availability:

Daily, 24 hours

Turnaround Time:

4 hours if received on Monday – Friday: 0700-1730 or Saturday: 1000-1300. 1 day if received outside of these regular working hours. Stats are done within 1 hour of receipt in the laboratory.

For urgent testing after hours, contact Children’s laboratory and they will call Fairview’s tech on call.

Special Instructions:

Patient should not be receiving heparin. If so, this should be noted on the request form. Heparin therapy can affect certain coagulation factors or assays, preclude their performance, or cause spurious results.

Indicate when specimen is drawn from a line or a heparin lock. Deliver immediately to the laboratory.


Specimen Type:

Whole blood


Light Blue top (Buffered Na Citrate 3.2%) tube

Draw Volume:

2.7 mL blood in a 3 mL tube

Processed Volume:

Specimens will be processed at reference lab facility if received within 4 hours of collection. Otherwise, specimens need to be processed at referring facility and provide minimum of two 0.5 mL specimens frozen at -70. Follow directions below under Special Processing.


Routine venipuncture. Do Not use the first 2 mL’s of blood collected.

Patients with Hematocrit levels of >55% must have a special tube made to adjust for the hematocrit, contact laboratory for special tube.

Fill tube completely. Mix thoroughly by gentle inversion.


Special Processing:

Lab Staff: Do Not centrifuge. Do Not freeze. Send to reference lab in original Vacutainer® at room temperature if within 4 hours of collection. Forward promptly.

If specimen is >4 hours old prior to shipment, process specimen as follows:
Spin sample collected in blue top tube(s) for 5 minutes on the Stat Spin centrifuge, remove plasma and transfer to a 4 mL BCS sample cup(s), spin remaining plasma again for 5 minutes in the Stat Spin Centrifuge. Transfer plasma into two labeled 10x75 mL plastic tubes with a minimum of 0.5 mL in each. Freeze at -70 and send specimens on dry ice to Fairview University.

Patient Preparation:

If the patient has a coagulation abnormality, apply direct pressure to the puncture site for 10 minutes; apply pressure bandage. Instruct the patient to leave the bandage on for 12 hours.

Sample Rejection:

Improper tube; clotted samples; underfilled tubes; overfilled tubes, mislabeled or unlabeled specimens


Reference Range:


Range (%):

<1 day:

61 – 194%

1 – 4 days:

61 – 139%

5 – 29 days:

55 – 121%

30 – 89 days:

58 – 124%

90 – 179 days:

56 – 102%

180 – 364 days:

55 – 91%

1 year:

60 - 140%

Critical Values:



Increased in patients who are pregnant or are taking oral contraceptives


APTT clotting time correction of factor 8 deficient plasma. Patient dilutions are compared to a known set of standard dilutions and a percentage is determined.


Fairview University Web Page February 2014

Harmening DH (1997) Clinical Hematology and Fundamentals of Hemostasis


5/27/2004: Reference ranges changed from 70-130% to 60-140%. Draw volume reduced from 4.5 mL in a 5 mL tube to 2.7 mL in a 3 mL tube.
10/7/2005: Reference ranges added for 0-5 days, previously only listed for greater than or equal to 1 year.
5/25/2010: Tubing patient specimens is no longer prohibited.
6/15/2011: Reference range update.
2/24/2014: Fairview specimen processing update.