Importance of Pretest Probability Score and D-Dimer Assay
Importance of Pretest Probability Score and D-Dimer Assay
Objective: The purpose of our study was to develop and validate a clinical score (the Hamilton score) for the assessment of lower limb deep venous thrombosis (DVT) and to determine the usefulness of this score and a D-dimer assay before a complete lower limb sonographic examination.
Subjects and Methods: Five hundred forty-two consecutive ambulatory patients presenting to the emergency department were prospectively recruited, of whom 16 patients were excluded from the study. Eighteen history and examination variables were collected by the emergency department physicians. The Simplify D-dimer assay and a complete, single lower limb sonographic examination were performed in all patients. All patients with a negative sonographic examination for DVT were followed up for 3 months, and all those with a positive sonographic examination were given anticoagulation therapy. The Hamilton score was developed using the data from the first 214 patients and was prospectively validated in the next 312 patients.
Results: The most significant factors associated with a diagnosis of DVT were immobilization of the lower limb, active malignancy, and a strong clinical suspicion of DVT without other diagnostic possibilities by the emergency department physicians. Other factors were bed rest or recent surgery, male sex, calf circumference difference greater than 3 cm, and erythema. The Hamilton score was developed with the following weights: immobilization of the lower limb (2 points), active malignancy (2 points), strong clinical suspicion of DVT without other diagnostic possibilities by the emergency physicians (2 points), bed rest or recent surgery (1 point), male sex (1 point), calf circumference difference greater than 3 cm (1 point), and erythema (1 point). A score of 3 or greater indicates a likely probability for DVT, and a score of 2 or less represents an unlikely probability for DVT. Of the 103 patients with an unlikely probability Hamilton score and a negative D-dimer assay, only one patient had isolated calf DVT. A combined diagnostic strategy of unlikely-probability Hamilton score and a negative D-dimer would have a negative predictive value of 99% (95% confidence interval, 94.7-100%).
Conclusion: An unlikely-probability Hamilton score and a negative Simplify D-dimer assay effectively exclude lower limb DVT, and a sonographic examination is unnecessary in this group of ambulatory emergency department patients.
Deep venous thrombosis (DVT) affects about 84 persons per 100,000 each year. Objective testing for DVT is essential because clinical assessment alone is unreliable. Untreated DVT is associated with a high risk of pulmonary embolism, and false diagnosis of DVT results in unnecessary anticoagulant therapy, which is associated with a risk of bleeding. Accurate diagnosis of DVT and prompt therapy are essential to reduce the risk of thromboembolic complications. DVT also predisposes patients to postthrombotic or postphlebitic syndrome in 40-75% cases.
Pretest probability score models, based on history and examination, for predicting the probability of DVT help clinicians improve the accuracy of their diagnosis of DVT. These models include the nine-component Wells score, the six-component St. Andre hospital score, the four-component Kahn score, and the six-component ambulatory score. Recently, the Wells score has been modified to include 10 components. The Wells score is a better predictor of DVT than are the Kahn and St. Andre's scores. The Wells score and the ambulatory score have similar operating characteristics.
However, the modified Wells score has limitations in discriminating patients likely to have DVT and those unlikely to have DVT. In a study involving 1,096 ambulatory outpatients, 601 patients (54.8%) were identified as unlikely to have DVT and 495 patients (45.2%) as likely to have DVT using the modified Wells score. This is despite the ambulatory population, which is expected to have a lower risk for DVT than hospital inpatients. The modified Wells score has overlapping redundant features, such as lower limb enlargement, calf enlargement, and pitting edema, that render the score less accurate in stratification and more cumbersome to calculate. Important risk factors such as prior history of DVT or pulmonary embolism, pregnancy, and the use of oral contraceptives were not considered when the Wells score was developed. Therefore, a pretest probability score needs to be developed that considers the important risk factors in the derivation population, stratifies patients more accurately into those having an unlikely probability and those having a likely probability, consists of no overlapping redundant features, and is easy to calculate.
The objective diagnosis of DVT of the lower limbs now relies mainly on the use of sonography. In symptomatic patients, sonography has shown to be highly specific and sensitive compared with venography for both proximal and distal DVT. It is safe to withhold anticoagulant therapy in patients with clinically suspected DVT after a negative complete lower limb (including calf veins) sonographic examination. The modified Wells score was based on a diagnosis of DVT using serial above-knee sonographic examinations rather than complete lower limb sonographic examinations.
In this study, we aimed to develop and validate a new pretest clinical probability score (the Hamilton score) with the objective of diagnosing DVT based on a single complete sonographic examination of a symptomatic lower limb and a 3-month clinical follow-up, and to determine the usefulness of an unlikely-probability Hamilton score and a negative Simplify D-dimer assay (Agen Biochemical) before a sonographic examination.
Objective: The purpose of our study was to develop and validate a clinical score (the Hamilton score) for the assessment of lower limb deep venous thrombosis (DVT) and to determine the usefulness of this score and a D-dimer assay before a complete lower limb sonographic examination.
Subjects and Methods: Five hundred forty-two consecutive ambulatory patients presenting to the emergency department were prospectively recruited, of whom 16 patients were excluded from the study. Eighteen history and examination variables were collected by the emergency department physicians. The Simplify D-dimer assay and a complete, single lower limb sonographic examination were performed in all patients. All patients with a negative sonographic examination for DVT were followed up for 3 months, and all those with a positive sonographic examination were given anticoagulation therapy. The Hamilton score was developed using the data from the first 214 patients and was prospectively validated in the next 312 patients.
Results: The most significant factors associated with a diagnosis of DVT were immobilization of the lower limb, active malignancy, and a strong clinical suspicion of DVT without other diagnostic possibilities by the emergency department physicians. Other factors were bed rest or recent surgery, male sex, calf circumference difference greater than 3 cm, and erythema. The Hamilton score was developed with the following weights: immobilization of the lower limb (2 points), active malignancy (2 points), strong clinical suspicion of DVT without other diagnostic possibilities by the emergency physicians (2 points), bed rest or recent surgery (1 point), male sex (1 point), calf circumference difference greater than 3 cm (1 point), and erythema (1 point). A score of 3 or greater indicates a likely probability for DVT, and a score of 2 or less represents an unlikely probability for DVT. Of the 103 patients with an unlikely probability Hamilton score and a negative D-dimer assay, only one patient had isolated calf DVT. A combined diagnostic strategy of unlikely-probability Hamilton score and a negative D-dimer would have a negative predictive value of 99% (95% confidence interval, 94.7-100%).
Conclusion: An unlikely-probability Hamilton score and a negative Simplify D-dimer assay effectively exclude lower limb DVT, and a sonographic examination is unnecessary in this group of ambulatory emergency department patients.
Deep venous thrombosis (DVT) affects about 84 persons per 100,000 each year. Objective testing for DVT is essential because clinical assessment alone is unreliable. Untreated DVT is associated with a high risk of pulmonary embolism, and false diagnosis of DVT results in unnecessary anticoagulant therapy, which is associated with a risk of bleeding. Accurate diagnosis of DVT and prompt therapy are essential to reduce the risk of thromboembolic complications. DVT also predisposes patients to postthrombotic or postphlebitic syndrome in 40-75% cases.
Pretest probability score models, based on history and examination, for predicting the probability of DVT help clinicians improve the accuracy of their diagnosis of DVT. These models include the nine-component Wells score, the six-component St. Andre hospital score, the four-component Kahn score, and the six-component ambulatory score. Recently, the Wells score has been modified to include 10 components. The Wells score is a better predictor of DVT than are the Kahn and St. Andre's scores. The Wells score and the ambulatory score have similar operating characteristics.
However, the modified Wells score has limitations in discriminating patients likely to have DVT and those unlikely to have DVT. In a study involving 1,096 ambulatory outpatients, 601 patients (54.8%) were identified as unlikely to have DVT and 495 patients (45.2%) as likely to have DVT using the modified Wells score. This is despite the ambulatory population, which is expected to have a lower risk for DVT than hospital inpatients. The modified Wells score has overlapping redundant features, such as lower limb enlargement, calf enlargement, and pitting edema, that render the score less accurate in stratification and more cumbersome to calculate. Important risk factors such as prior history of DVT or pulmonary embolism, pregnancy, and the use of oral contraceptives were not considered when the Wells score was developed. Therefore, a pretest probability score needs to be developed that considers the important risk factors in the derivation population, stratifies patients more accurately into those having an unlikely probability and those having a likely probability, consists of no overlapping redundant features, and is easy to calculate.
The objective diagnosis of DVT of the lower limbs now relies mainly on the use of sonography. In symptomatic patients, sonography has shown to be highly specific and sensitive compared with venography for both proximal and distal DVT. It is safe to withhold anticoagulant therapy in patients with clinically suspected DVT after a negative complete lower limb (including calf veins) sonographic examination. The modified Wells score was based on a diagnosis of DVT using serial above-knee sonographic examinations rather than complete lower limb sonographic examinations.
In this study, we aimed to develop and validate a new pretest clinical probability score (the Hamilton score) with the objective of diagnosing DVT based on a single complete sonographic examination of a symptomatic lower limb and a 3-month clinical follow-up, and to determine the usefulness of an unlikely-probability Hamilton score and a negative Simplify D-dimer assay (Agen Biochemical) before a sonographic examination.