Clinical Associations and Significance of Biphasic aPTT Transmittance Waveforms.

Many modern automated coagulometers determine coagulation parameters such as the PT and aPTT using optical endpoints. One instrument (MDA-180, BioMerieux, Durham, NC) continuously monitors changes in optical transmittance through the specimen over the course of clot formation, and is able to analyze measurements derived from the resulting waveform. The waveform is typically sigmoid, with a sharp drop in transmittance at the time of clot formation. In some specimens, a biphasic waveform (BPW) pattern has been observed, in which the normally flat pre-coagulation segment has a negative slope prior to the sharp drop in transmittance associated with clot formation. The BPW pattern has been associated with sepsis, DIC, and increased mortality in adult patients.

The Special Haemostasis Laboratory of the Health Sciences Centre in Winnipeg, Canada uses the MDA-180 for all automated coagulation assays. Over a two-year period (August, 2002 to July, 2004), a BPW was identified in 21 adult and 12 pediatric patients. Hospital records of these patients were reviewed for details of their clinical condition, and coagulation test results were examined for presence of hemostatic abnormalities.

Sepsis was a common diagnosis at the time of detection of the BPW, seen in 57% of the adults and 42% of the children. However, 4 adults (19%) and 4 children (33%) were identified during routine investigations for clinical bleeding or thrombophilia. In contrast to previously reported studies, DIC was less prevalent, seen in only 7 (33%) of the adults and 3 (25%) of the children. The presence of lupus anticoagulants, alone or in conjunction with other coagulation abnormalities, was observed in 8 adults (38%) and 9 children (75%). This association has not previously been reported. Nine adults (43%) and four children (33%) died, all from complications of sepsis.

Despite the small sample size, this study questions the clinical utility and specificity of the BPW as an indicator of sepsis and DIC. The association with DIC seems particularly weak in the pediatric population, in which the BPW has not been previously evaluated. Further study is required to determine the strength of the association between the BPW and DIC, and to identify other clinical and laboratory conditions, such as lupus anticoagulants, which may confound this association.