The hidden sepsis marker: aPTT waveform analysis.

Thromb Haemost 2008; 100: 9–10 Downey et al. published a paper in 1997 entitled ‘Novel and diagnostically applicable information from optical waveform analysis of blood coagulation in disseminated intravascular coagulation’ (1). Using a new automated coagulation analyzer, the MDA-180, the authors observed that during measurement of the aPTT, some samples became turbid immediately after addition of the calcium chloride reagent, well before clot formation. These plasma samples were mainly from intensive care unit (ICU) patients, which also fulfilled the diagnostic criteria for disseminated intravascular coagulation (DIC). The ‘biphasic waveform’ (BPW) recorded during optical measurement of the aPTT was thus introduced as a diagnostic marker for DIC (2). The authors found BPW also in some patients without DIC, and speculated that the phenomenon was related to coagulation activation or presence of pre-formed fibrin complexes. At that time, our laboratory was involved in an analysis of the effects of ancrod, a thrombin-like snake venom enzyme used for treatment of ischemic stroke (3). Ancrod induces massive intravascular fibrin formation, but none of our probands treated with ancrod developed BPW, indicating that BPW was not related to intravascular fibrin formation. Finally, Toh et al. were able to show that BPW was due to calcium-dependent complex formation between C-reactive protein (CRP) and very low density lipoprotein (VLDL) (4). Actually, this phenomenon had been described 20 years earlier. Cabana et al. showed that VLDL formed precipitating complexes with CRP, and these complexes were not observed in the presence of EDTA (5). In the same year, Hulman et al. reported that the serum of acutely ill patients agglutinated fat emulsions prepared from soybean oil designated for intravenous infusions, resulting in ‘creaming’ of the sera (6). Free calcium ions were necessary for ‘creaming’, and no ‘creaming’ was observed if citrate was added to the sera. The authors concluded that ‘creaming’ was a property of acute phase sera, and that this phenomenon is the explanation for adverse reactions to intravenous lipid emulsions, related to lipid microembolism, such as fever, shivering, precordial pains, nausea and vomiting. A ‘fat emulsion agglutination test’ was developed for measurement of CRP (7). It was later shown that the ‘creaming’ phenomenon in response to intravenous lipids was only observed in patients with highVLDL levels (8). Rowe et al. further characterized the interaction between CRP and VLDL and concluded that CRP may be related in some way to lipoprotein metabolism (9). It was also shown in experiments on rabbits that the CRP-VLDL complexes formed in acute phase serum contained predominantly β-VLDL, an abnormal apo-B containing lipoprotein low in apo-E content (10, 11). Inflammatory stimuli such as endotoxin induce the upregulation of VLDL secretion in the liver (12). Bennett et al. reported that endotoxin has a distinct effect on structural properties of VLDL, resulting in improved utilization by the heart as energy substrate (13). The authors did not consider the possibility that complex formation of CRP and VLDL might be involved. BPW is an indicator of a systemic inflammatory response, as observed in sepsis. Chopin et al. studied 187 patients with 217 episodes of systemic inflammatory response syndrome, of which 34 were classified as sepsis, 26 as severe sepsis, and 50 as septic shock. The diagnostic sensitivity and specificity of BPW for the combined group of severe sepsis and septic shock was 92% and 67%, respectively. Both CRP and procalcitonin displayed a lower diagnostic sensitivity (14). Another recent study showed a sensitivity of BPW for sepsis of 81%, with a specificity of 76% in ICU patients (15). Combination of aPTT waveform analysis with procalcitonin measurement did not increase sensitivity but raised specificity to 94%. In our own study on ICU patients, the diagnostic sensitivity of BPW for sepsis was 74%, with a specificity of 81% (16). Within the group of ICU patients with systemic inflammatory response syndrome, BPW identifies a group with increased mortality rate. In the study of Toh et al., the mortality rate of patients with BPW was 44%, compared to 26% in the patients without BPW (17). In the study of Bakhtiari et al., mortality of patients with and without BPW was 43% and 32%, respectively (18). In our study, the mortality rate of ICU patients with and without BPW was 36.8% and 13.1%, respectively (16). Use of the aPTT waveform analysis is not limited to ICU patients. Smith et al. have shown that also non-ICU patients with BPW are more likely to have positive blood cultures (19). Similarly, the study now published by Hussain et al. (20) shows that BPW can identify patients with sepsis within a specific high-risk patient group. Myelosuppressive therapy results in neutropenia