Background: D-dimer is clinically useful for its high sensitivity and negative predictive value as a useful “rule out” test for venous thromboembolism. Nevertheless, the D-dimer assay is not specific and often elevated in states of systemic inflammation or illness.Stasis of blood flow, Endothelial injury, and hypercoagulability are the tenets of thrombus formation. When any one of these is disrupted, thrombosis can occur. In this study, we will focus on the reduction of venous blood flow from vascular dilatation and examine if dilation increases the formation of D-dimer products.Similar studies linked increasing diameter of the inferior vena cava (IVC) to the risk of thromboembolism. However, to our knowledge, there have been none comparing the IVC diameter size to D-dimer levels. Such an association could be useful in developing a risk calculator for thromboembolism or increasing the specificity of D-dimer testing.
Methods: IRB exemption was obtained. Data was taken from consecutive patients visiting the Emergency Department over a 10-year period. Inclusion criteria was defined as an individual ≥ 18 years old who underwent a computerized tomography scan (CT) and had a detectable D-dimer serum test on the same day of their visit.ICD codes were used to exclude patients with tobacco use, active thrombus, or malignancy. White blood cell count of ≥ 12.9 x 103 cells/mL and a single oral temperature of ≥ 38.3ºC were used to remove individuals at risk for SIRS. Additionally, we excluded individuals with a positive pregnancy test, or a blood thinner listed on their active medication list, to screen for hypercoagulable states and those at higher risk for thrombosis. Through chart review, individuals were removed who underwent any surgical procedure within 6 months of presentation or had a trauma alert during their visit.IVC measurements were taken from abdominal CT scans that used a maximum slice interval of 5mm. IVC short axis diameter was measured 1.5cm above the left renal vein but below the liver parenchyma. This location has demonstrated minimal change in diameter with respiration and closely estimates IVC average diameter. A detectable D-dimer level was set at ≥ 100ng/mL.Single linear regression was used. Statistical significance was evaluated at P ≤ 0.05. Variables of interest included D-dimer levels and IVC diameter.
Results: In all, 111 patients’ medical records were obtained. The mean patient age was 56 and 66.3% were female. Among the patients, the mean IVC diameter was 18.2mm, and the mean D-dimer was 930.1ng/mL.The unadjusted linear regression analysis showed no statistically significant association between IVC diameter and D-dimer levels (P = 0.32). R-squared (R2= 0.0098) demonstrated that IVC variability is not explained by D-dimer levels. Furthermore, correlation factor (R= 0.099) meant that there is a very weak direct relationship seen in our data, but it was not significant enough to make an association. Since our P-Value ≥ α (0.05), we accept our null hypothesis that there is no association between D-dimer value and IVC diameter.
Conclusions: The main finding of this study established that there is no association between inferior vena cava diameter and D-dimer levels. The current knowledge regarding D-dimer synthesis does demonstrate many factors that can influence its formation within the vasculature. It is reasonable to conclude that D-dimer product formation is multifactorial, however, the diameter of the inferior vena cava likely does not contribute, based on these findings.