STUDY SUMMARY
Using age-adjusted d-dimer cutoffs significantly reduced false-positives
Schouten et al1 performed a systematic review and meta-analysis of studies of older patients with suspected VTE who had d-dimer testing using both conventional and age-adjusted cutoff values. The authors searched Medline and Embase for studies that were performed in outpatient, inpatient, or emergency department settings. They excluded studies of high-risk patients, specifically perioperative patients and those who’d had VTE, cancer, or a coagulation disorder.
Five high-quality studies of 13 cohorts were included in this analysis (N = 12,497; 6,969 patients older than 50). Each of these studies was a retrospective analysis of patients with a low clinical probability of VTE, as determined by Geneva or Wells scoring. The authors calculated the VTE prevalence and d-dimer sensitivity and specificity for patients ages ≤ 50, 51 to 60, 61 to 70, 71 to 80, and > 80.
The specificity of the conventional d-dimer cutoff value for VTE decreased with age from 57.6% in those ages 51 to 60 to 14.7% in those older than 80. When age-adjusted cutoffs were used (age in years × 10 μg/L), specificities improved in all age categories, particularly for older patients. For example, using age-adjusted cutoff values improved specificity to 62.3% in patients ages 51 to 60 and to 35.2% in those older than 80 (see table). Using a hypothetical model, Schouten et al1 calculated that applying age-adjusted cutoff values would exclude VTE in 303/1,000 patients older than 80, compared with 124/1,000 when using the conventional cutoff.
The benefit of using an age-adjusted cutoff is the ability to exclude VTE in more patients (1 out of 3 in those older than 80) while not significantly increasing the number of missed VTE. In fact, the number of missed cases in the older population using the age-adjusted cutoff (approximately 1 to 4 per 1,000 patients) is comparable to the false-negative rate in those ages 50 and younger (3 per 1,000). The advantages are most notable with the use of enzyme linked fluorescent assays because these assays have a higher sensitivity and a trend toward lower specificity compared with other assays.
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