D-dimer cut-off adjusted to age performs better for exclusion of pulmonary embolism in patients over 75 years

A D-dimer (DD) test improves the diagnosis of PE (PE) when combined with clinical scores. However, as DD levels increase physiologically with age, this testing has less specificity in older patients. Douma et al. (1). proposed the use of an age adjusted DD cut-off to increase the specificity of this test.

We performed chart reviews of patients, older than 75 years, hospitalized for suspicion of PE in 2010-2011 (n = 165). PE was assessed with either pulmonary scintigraphy (PS, n = 64) and/or pulmonary computed tomography (PC, n = 101). We compared the specificity, sensitivity and false negatives rates of an age adjusted DD cut-off level ("ADC" = (patient's age x 0.01) microg/ml) with those of the conventional cut off level ("CDC" = 0.5 microg/ml).

PE was confirmed in 45 cases. In the 120 patients with no PE (negative PS or PC), 7 cases had CDC below cut-off levels, while 28 cases had an ADC below cutoff level. The use of the ADC thus increased the specificity (ADC: 23% vs CDC: 6%, p = 0.0001), and this was obtained without significant loss of sensitivity (ADC: 96% vs CDC: 98%, ns). Patients were clinically assessed with the revised Geneva scores. In the negative PE group, the number of patients classified with low, moderate or high clinical probability of PE were 31, 81 and 8, respectively. The percentage of patients with DD values below cut-off values was 4%, 0.8% and 0.8%, respectively using the CDC and 9%, 12% and 2.5% using the ADC.

In this age group, the specificity of ADC was found superior to that of the CDC. The clinical use of the ADC might be associated with less useless diagnosis procedures, without significant increase in rate of diagnosis failure.