Factor Assay

Are commonly undertaken when there is prolongation of the APTT or PT suggesting a deficiency of one or more clotting proteins.

- Sample type:

Collect specimen in blue top (3.2% sodium citrate) tube. If multiple tests are being drawn, draw coagulation studies before additive-containing tubes such as the EDTA, heparin, or clot activator (SST) tubes

- Uses:

To determine the cause of an unexpected, prolonged PT or a PTT. This test is performed after mixing studies have been performed and a deficiency of one or more coagulation factors is suspected. Factor assays are able to identify specific factor deficiencies or inhibitors.

- Precautions:

Simple precautions like collection of blood samples in smaller volumes in separate tubes, assaying multiple coagulation factors in the blood samples helped to offer diagnoses in all the analyses. Accurate blood sampling is a safe technique for the diagnosis of many of the bleeding disorders in places where genetic diagnostic services are not available.

- Interfering factors:

Decreased factor VIII activity may be due to: Hemophilia A (a bleeding disorder caused by a lack of blood clotting factor VIII) Disorder in which the proteins that control blood clotting become over active disseminated intravascular coagulation (DIC) Presence of a Factor VIII inhibitor (antibody)

- Pre analytical errors:

1) Sample collection

2) Collection tubes

3) Sample delivery to the laboratory

- Corrective action:

The degree of correction of the clotting time when the plasma is added to a clotting system specifically deficient in the clotting factor to be measured, allows the level of that clotting factor to be determined e.g. Factor IX deficient plasma is used to assay the level of Factor IX.

- Post analytical errors:

1) Release of the laboratory test report

2) Reporting of test results

- reference range:

The normal value is 50% to 200% of the laboratory control or reference value

Normal ranges for factor VIII levels are 50% to 150%.