| Objective:Deep vein thrombosis(DVT)was abnormal blood coagulation in the lower extremity deep vein that obstructed the lumen and caused venous reflux obstacles was a common complication in patients with fractures.And when severe,it can be life-threatening.Levels of D-dimer were used for the diagnosis of DVT in clinical practice.Age was a risk factor for DVT occurrence.D-dimer concentrations increased with age within a certain range,resulting in a reduction in the specificity of diagnosis in the elderly population.The Venous thromboembolism in adults guide updated by the National Institute for Health and Care Excellence(NICN)in 2020,stated that the age correction formula(age×0.01 mg/L,hereafter referred to as classical formulation)was recommended to be used in people over 50.However,the classical formulation was based on the diagnosis of pulmonary embolism in the general European populations,and its diagnostic efficiency in the elderly Asian population with fractures was unknown.Thus,this study aims to describe the characteristics of D-dimer level increasing with age in elderly hip fracture patients and try to establish a new age-adjusted D-dimer formula(hereafter referred to as the new formulation)to improve the diagnostic specificity and screening efficiency in the elderly patients with hip fractures.Methods:In this study,we retrospectively collected 3972 elderly patients with acute hip fractures who were admitted to the trauma emergency center of the Third Hospital of Hebei Medical University from June 2016 to June 2019.All patients were admitted to the trauma emergency center of the Third Hospital of Hebei Medical University from June 2016 to June 2019.Before surgery,all patients underwent D-dimer detection(immunofluorescence tomography)and color duplex ultrasonography to confirm whether they had DVT.Simple linear fitting was carried out for age and D-dimer level,considering that the steps for each age were too tedious,therefore,based on the relevant step of the classical formulation and the expert opinion,every five years were classified in one group.The included patients were divided into six groups according to age(age group distance is 5 years old):65～69 years old,70～74 years old,75～79 years old,80～84 years old,and 85～89 years old,age greater than or equal to 90 years old.The receiver operating characteristic(ROC)curves were established in the six age groups,and the optimal clinical cut-off values for the diagnosis of DVT were established according to the ROC curve.And then the cut-off values of each group were analyzed by linear regression analysis to determine the new formula.The 7 indicators including sensitivity,specificity,and so on,are calculated and compared to evaluate the screening efficiency when three different formulas were used in elderly patients with hip fractures.Results:There were 2759 patients included,887 males and 1872 females,with a median age of 78 years.280 patients were diagnosed with preoperative DVT.The median of plasma D-dimer levels was 1.13 mg/L in the overall population,and the median(interquartile range)of plasma D-dimer levels in the six age groups were 0.94(2.23)mg/L,0.99(2.15)mg/L,1.03(2.25)mg/L,1.29(2.05)mg/L,1.31(1.88)mg/L,1.60(2.31)mg/L.The D-dimer level showed an increasing trend with age in all populations.The optimal cutoff values for the six age groups were 0.715 mg/L,1.17 mg/L,1.62 mg/L,1.665mg/L,1.69 mg/L and 1.985 mg/L,respectively.The calculated coefficient of the age-adjusted formula was 0.02 mg/L(R~2=0.874,P<0.05).When the new age-adjusted formula was applied in people with hip fractures and≥65years,the specificity was 61%,clearly higher than those for conventional threshold(0.5 mg/L,37%)or classic age-adjusted D-dimer formula(age×0.01mg/L,22%).In contrast,the sensitivity was lower than that(59%vs 77%or85%)when the classic D-dimer age-adjusted cutoff value or conventional threshold was used.The positive predictive values(15%,11%,and 12%)and the negative predictive values(93%,93%,and 94%)were comparable when the new age-adjusted D-dimer formula,the conventional threshold,and the classic age-adjusted formula were applied.Conclusions:The level of D-dimer was significantly correlated positively with age.Compared with the traditional threshold and classical formula,a significant improvement in specificity was gained when the new formula was used,but decreased sensitivity was observed for the preoperative DVT screening and evaluation in patients with hip fractures≥65 years.When clinicians used the new formula,they should combine symptoms,and another thrombosis-related laboratory parameters such as activated thromboplastin time,red cell distribution width,and fibrinogen.The new formula could improve the detection rate of patients without DVT and the effectiveness of preoperative DVT screening programs in the elderly patients with hip fractures.It showed a benefit in saving medical resources. |
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