New prediction tool for patients at risk of venous thromboembolism validated

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Investigators in The Netherlands, France and Belgium have developed a risk assessment model for venous thromboembolism (VTE). Published by The Lancet in EClinicalMedicine, the TRiP(cast) score (thrombosis risk prediction following cast immobilisation) is described as “a helpful tool in daily clinical practice to accurately stratify patients in high- versus low-risk categories, in order to guide thromboprophylaxis prescribing”.

According to Banne Nemeth (Leiden University Medical Center, Leiden, The Netherlands) and colleagues, lower-limb trauma patients who require immobilisation are at a higher risk of VTE. “While thromboprophylaxis for all patients seems not effective, targeted thromboprophylaxis in high-risk patients may be an appropriate alternative,” the authors argue.

They continue: “For instance, patients with a high risk may benefit from an intensified regimen of thromboprophylaxis, whereas patients with a low risk can be [safely] withheld from treatment. By doing so, both thrombosis and bleeding risk can be reduced to a minimum.”

The two-fold aim of Nemeth et al’s study was to develop and validate a new score for the identification of immobilised patients at a low or high risk of VTE. As part of the investigation, data from the MEGA study, a case-control study into the aetiology of VTE, were used to assess the performance of the TRiP(cast) score in comparison to the previous Leiden-TRiP(cast) score and TIP score (for trauma, immobilisation and patients characteristics).

In addition, results of the POT-CAST randomised trial—on the effectiveness of thromboprophylaxis following cast immobilisation—were used for the external validation of the TRiP(cast) score. “Model discrimination was calculated by estimating the ‘Area Under the Curve’,” the authors explain, adding that “for model calibration, observed and predicted risks were assessed.”

A total of 14 items were included in the TRiP(cast) score, which consisted of three components: trauma, immobilisation, and patient characteristics. One item related to trauma severity (or type of trauma), one to the type of immobilisation, and the other 12 to patients’ characteristics.

Detailing how the score works, Nemeth et al write: “Each item can be scored on a scale of one to four and the sum of these scores results in the TRiP(cast) score. For instance, a 50-year-old male with a BMI of 30kg/m² receives three points (including one point for being older than 35 years, one point for male sex, and one point for having a BMI of 25 or higher and less than 35kg/m²). If this patient has a bi-trimalleolar ankle fracture (two points) requiring lower-leg cast (two points), this results in a total of seven points.”

Validation analyses of the tool showed an area under the curve of 0.74 (95% [CI], 0.61–0.87) in the complete dataset (n=1250) and 0.72 (95%CI, 0.60–0.84) in the imputed data set (n=1435), while the calibration plot demonstrated “the degree of agreement between the observed and predicted risks (intercept 0.0016 and slope 0.933)”. Moreover, the authors underline that “using a cut-off score of seven points in the POT-CAST trial (incidence 1.6%), the sensitivity, specificity, positive, and negative predictive values were 76.1%, 51.2%, 2.5%, and 99.2%, respectively”.

Commenting on these findings further, they say: “The TRiP(cast) score exhibited good performance in the external validation […] and the observed and predicted risk were in concordance. Using less than seven points as [the] cut-off, the TRiP(cast) score allows identification of an important subgroup of patients with a low risk of symptomatic VTE (mean absolute risk of 0.8%) who may not require any thromboprophylactic treatment.”

Despite the positive outcome of the study, which was validated in a large cohort of patients, Nemeth and colleagues also emphasise that the ultimate cut-off and “corresponding optimal treatment” require determination in a larger management study. They also highlight the overriding problem that the current situation needs improvement, as “2% of patients develop VTE despite thromboprophylaxis”.

“In conclusion, the TRiP(cast) score was developed and validated to predict VTE risk following lower-limb cast or brace immobilisation. Thanks to a smartphone application, it can easily be implemented in future research and clinical practice to accurately stratify patients in risk categories and to help in decision making for individualised thromboprophylaxis,” state Nemeth et al in closing.


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