Preoperative Venous Circumference-Squared-to-Area Ratio (C2/A) and D-dimer for Deep Vein Thrombosis Prediction After Orthopedic Surgery.

DVT occurred in 37 of 150 adults (24.7%) during the first 7 postoperative days following orthopedic surgery.

• 150 adults undergoing orthopedic surgery were enrolled in this prospective observational study.
• 37 patients developed DVT and 113 did not.
• Postoperative ultrasound was performed at 12-hour intervals for 7 days under a prespecified intensified study-surveillance schedule used only for outcome ascertainment.

Preoperative common femoral vein C2/A had an AUC of 0.893 for predicting postoperative DVT.

• The area under the receiver operating characteristic curve (AUC) for common femoral vein C2/A was 0.893.
• C2/A was calculated as circumference squared divided by area, with both measured separately at end-expiration using the ultrasound system's built-in measurement package during the same acquisition cycle.
• This was among the highest single-marker AUC values reported in the study.

Preoperative popliteal vein C2/A had the highest single-marker AUC of 0.906 for DVT prediction.

• The AUC for popliteal vein C2/A was 0.906.
• Superficial femoral vein C2/A had an AUC of 0.817.
• D-dimer alone had an AUC of 0.834.

The prespecified superficial femoral vein C2/A plus D-dimer combination model showed an apparent AUC of 0.887 and a cross-validated out-of-fold AUC of 0.877.

• The originally specified superficial femoral vein C2/A plus D-dimer model had an apparent AUC of 0.887.
• Stratified 5-fold cross-validated out-of-fold AUC was 0.877, suggesting limited overfitting.
• This was the pre-specified primary combined model.

A 5-variable exploratory model achieved an out-of-fold AUC of 0.938 for DVT prediction.

• The 5-variable exploratory model had an out-of-fold area under the curve of 0.938.
• This model was described as exploratory, exceeding the performance of the prespecified 2-variable model.
• The study authors did not designate this as the primary model.

Using cohort-derived thresholds, DVT occurred in 0 of 78 patients with neither marker elevated, 15 of 50 with one marker elevated, and 22 of 22 with both markers elevated.

• Cohort-derived threshold for superficial femoral vein C2/A was 16.26.
• Cohort-derived threshold for D-dimer was 2.15 mg/L FEU.
• All 22 patients with both markers above threshold developed DVT (100%).
• No DVT occurred among the 78 patients with neither marker elevated.
• The authors noted these thresholds are exploratory and require external validation.

C2/A was measured preoperatively as a single baseline measurement using ultrasound at end-expiration.

• Preoperative circumference (C) and area (A) were measured separately at end-expiration with the ultrasound system's built-in measurement package during the same acquisition cycle.
• Investigators calculated C2/A as C squared divided by A.
• All revision analyses used C2/A recalculated from the retained C and A fields to apply the rule consistently to the retained participant-level dataset.
• Only a single preoperative baseline measurement was used.