Age-dependent patterns of D-dimer and APTT for VTE in severe pneumonia: a multicenter retrospective study

To investigate age-stratified patterns of admission D-dimer and activated partial thromboplastin time (APTT) and their complementary value for venous thromboembolism (VTE) detection in severe community-acquired pneumonia (SCAP). This multicenter retrospective study consecutively enrolled 577 patients with SCAP admitted to two tertiary hospitals from January 2019 to December 2023. Admission coagulation parameters were compared using the Mann-Whitney U test. D-dimer values were natural log-transformed and analyzed using generalized linear models (GLMs) with a Gamma distribution and log link function. Additionally, activated partial thromboplastin time (APTT), fibrinogen, prothrombin time, and international normalized ratio (INR) were fitted using Gaussian GLMs with an identity link, each adjusted for nine prespecified covariates. The independent contribution of Ln (D-dimer) to VTE was assessed through multivariable logistic regression, with discrimination evaluated by the area under the receiver operating characteristic curve (AUC). VTE occurred in 86 of 577 patients (14.9%). The VTE group demonstrated significantly higher D-dimer levels (Z = −5.785, P < 0.001). Adjusted generalized linear models (GLMs) confirmed markedly elevated Ln(D-dimer) (Wald χ² = 32.186, P < 0.001) and reduced APTT (Wald χ² = 3.935, P = 0.047) in the VTE cohort. The interaction between age and VTE did not reach statistical significance (Ln(D-dimer): P = 0.666; APTT: P = 0.075). In age-stratified analyses, significant differences in Ln (D-dimer) persisted across both age groups (both P < 0.001), whereas APTT shortening was limited to patients aged < 65 years (−5.80 s, 95% CI, −10.55 to −1.05; P = 0.017) and was not observed in those aged ≥ 65 years (−0.34 s, 95% CI, −4.06 to 3.39; P = 0.859). Ln (D-dimer) was an independent predictor of VTE (adjusted OR 2.462, 95% CI, 1.789 to 3.388, P < 0.001), with an area under the curve (AUC) of 0.747 (95% CI, 0.689 to 0.805). In SCAP inpatients, VTE was linked to elevated D-dimer levels and a shortened APTT. The association with D-dimer was consistent across all age groups, whereas the shortening of APTT was primarily observed in younger patients. These age-stratified findings are exploratory due to the non-significant interaction ( P = 0.075) and require prospective validation.