Parental preferences on diagnostic imaging tests for paediatric appendicitis.

OBJECTIVES: To determine parental preferences for diagnostic imaging tests (DITs) for paediatric appendicitis, to rank the attributes impacting the DIT selection and to identify DIT attributes that would cause parents to switch their DIT. METHODS: Parents of children who had an abdominal ultrasound (US) for right lower quadrant pain were interviewed. Two DITs were compared at a time, parents were asked to indicate their preferred test and to rank its attributes according to the impact each attribute had on their selection. The strength of their preference for the chosen DIT was measured by systematically adjusting attributes of the chosen DIT until the parent changed their choice. RESULTS: Fifty parents were interviewed. For US versus CT, more parents preferred US (68%, P=0.02) with higher importance ranks for cancer risk (P<0.0001), test accuracy (P=0.04), pain during test (P=0.3), and scan length (P<0.0001); and lower ranks for sedation (P=0.02), intravenous (IV) (P<0.02), and oral contrast (P=0.06). For US versus MRI, parents preferred MRI (78%, P<0.0001) with higher importance ranks for accuracy (P=0.2), pain during test (P=0.06), and scan length (P=0.06); and lower for noise (P<0.0001), claustrophobia (P<0.0001), use of IV contrast (P=0.06), and sedation (P=0.2). CONCLUSION: US and MRI were the DIT preferred by parents for the investigation of acute paediatric appendicitis.

By increasing the affinity of heparin for fibrin, Zn(2+) promotes the formation of a ternary heparin-thrombin-fibrin complex that protects thrombin from inhibition by antithrombin.

Heparin binds fibrin and, by bridging thrombin onto fibrin, promotes the formation of a ternary heparin-thrombin-fibrin complex that protects thrombin from inhibition by antithrombin. Because thrombin binds γ(A)/γ'-fibrin, a variant with an extended γ-chain, with higher affinity than the bulk γ(A)/γ(A)-fibrin, γ(A)/γ'-fibrin affords bound thrombin more protection from inhibition by antithrombin-heparin. We examined the effect of Zn(2+) on heparin-thrombin-fibrin complex formation because Zn(2+) modulates heparin-protein interactions. Zn(2+) increased the affinity of heparin for γ(A)/γ(A)- and γ(A)/γ'-fibrin by 4.3- and 3.7-fold, respectively, but had no effect on the affinity of thrombin for either form of fibrin. In contrast, in the presence of heparin, Zn(2+) increased the affinity of thrombin for γ(A)/γ(A)-fibrin 4-fold (from a K(d) value of 0.8 to 0.2 µM) and slowed the rate of thrombin dissociation from γ(A)/γ(A)-fibrin clots. These findings suggest that Zn(2+) enhances the formation of ternary heparin-thrombin-fibrin complexes with γ(A)/γ(A)-fibrin but does not influence the already high affinity interaction of thrombin with γ(A)/γ'-fibrin. Consistent with this concept, in the presence of Zn(2+), γ(A)/γ(A)-fibrin protected thrombin from inhibition by antithrombin-heparin to a similar extent as γ(A)/γ'-fibrin. Therefore, by enhancing the binding of heparin to fibrin, physiological concentrations of Zn(2+) render fibrin-bound thrombin more protected from inhibition by antithrombin. Because fibrin-bound thrombin can trigger thrombus expansion, these findings help to explain why recurrent thrombosis can occur despite heparin treatment.