FACTOR IX BETHESDA TITER

Test Code

500443

CPT Codes
85250; 85335

Includes

"

Factor IX activity; factor IX Bethesda titer (Bethesda titer is not indicated and is cancelled if the factor activity is >40%)
"

Preferred Specimen

plasma

Minimum Volume

"4 mL (2 mL in each of two tubes)
"

Instructions

"Do not draw from an arm with a heparin lock or heparinized catheter.
"

Transport Container

"Blue-top (sodium citrate) tubes
"

Transport Temperature

frozen

Methodology
"The factor IX inhibitor (Bethesda titer) assay is performed using an activated partial thromboplastin time (aPTT)-based system.6 Serial dilutions are made of patient plasma with veronal buffered saline, then mixed with normal plasma containing close to 100% factor IX activity and are then incubated for two hours. An aPTT-based factor IX assay using factor IX-depleted plasma substrate is then performed on these incubated mixtures. Results are compared to those of incubated normal plasma. One Bethesda unit is defined as the amount of factor IX inhibitor that neutralized 0.5 IU of factor IX in this system. The number of serial dilutions tested is based on the anticipated level of the inhibitor. "

Limitations

"Autoimmune inhibitors that demonstrate second order kinetics cannot be accurately measured in the Bethesda titer system.6 If there is residual coagulation factor activity, it could falsely lower the Bethesda titer result. Lupus anticoagulant activity and antithrombotic agents that function as inhibitors should be ruled out prior to assaying for factor inhibitors in order to avoid factitious results. Some inhibitors may fully neutralize factors in less than two hours.
"

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.