Description

Panel includes: PTT and Heparin PTT, Corrected

PTTs for patients on heparin that do not agree with heparin levels measured by the anti-Xa heparin activity assay are termed discordant. The most common cause of discordant PTTs is a prolonged baseline PTT that alters the response of the PTT to heparin producing falsely high heparin PTTs compared to the anti-Xa heparin activity. Reasons for a prolonged baseline PTT include factor deficiency and deficiency in contact activation, including contact factor deficiencies and phospholipid neutralization by lupus inhibitors. In most cases the heparin activity result is a better indication of the anticoagulant effect of unfractionated heparin therapy as it is sensitive to only heparin and antithrombin levels in plasma. The heparin activity result, however, can be falsely lowered by increased levels of bilirubin and/or hemoglobin. With high levels of hemolysis and/or icterus the anti-Xa heparin activity assay can fail due to saturation of the spectrophotometer, leaving the PTT as the only option for UFH monitoring in these patients.

To adjust for the effect of prolonged baseline PTTs, a baseline-corrected PTT is calculated. The baseline PTT on heparin is determined using automated heparin neutralization with protamine but is not reported.

The Discordant Heparin Panel reports two results

1) Patients original PTT on heparin = PTT

2) Baseline-corrected PTT on heparin = Heparin PTT, Corrected

If the baseline PTT is normal, the original PTT and Heparin PTT, Corrected are close to the same value indicating concordance. If the original PTT and Heparin PTT, Corrected are substantially different it indicates PTT discordance and the Heparin PTT, Corrected should be used for heparin monitoring with a PTT heparin therapeutic range of 66 to 108 sec.

Note: Heparin PTT, Corrected - calculation unavailable for PTT>200 seconds.