d-dimer and aortic dissection

RAGING HYPOTHETICAL:

--your patient arrives complaining of severe chest pain radiating to the back
--you fear aortic dissection
--you've heard about this d-dimer thing...but is it ready for prime-time?




HIGH IN PE/DISSECTION, NOT SO MUCH IN MI: (PMID: 21478122)
--purpose of this research was to define the D-dimer value for discrimination between AAD, PE and AMI.
--consecutive series of 35 AAD, 22 PE and 206 AMI patients


--D-dimer values of patients with AAD (32.9 ± 66.7 g/ml, p<0.001) and PE (28.5 ± 23.6 g/ ml, p<0.001) were significantly higher than those of AMI patients (2.1 ± 3.7 g/ml).
--A cutoff value of 5.0 g/ ml was effective in distinguishing AAD and PE from AMI, with a sensitivity of 68% and a specificity of 90% (ok, but not great)




GOOD SENSITIVITY IS PROMISING... (PMID: 21296332)
--Review and meta-analysis to examine use of d-dimer as screening tool for aortic dissection.
--A value of 500 ng/ml was defined as the threshold for a positive plasma DD finding because it is widely used for ruling out pulmonary emboli.
--Identified 7 studies involving 298 subjects with aortic dissection and 436 without.


--When data were pooled across studies:

• sensitivity high (0.97, 95% confidence interval [CI] 0.94 to 0.99)
• negative predictive value high (0.96, 95% CI 0.93 to 0.98)
• specificity low (0.56, 95% CI 0.51 to 0.60)
• positive predictive value low (0.60, 95% CI 0.55 to 0.66) 

--In conclusion, our meta-analysis suggests that plasma DD <500 ng/ml is a useful screening tool to identify patients who do not have AAD.




NOT QUITE READY?  (PMID: 21546117)
--There is inadequate evidence to support the use of D-dimer to exclude acute aortic dissection.


--registry data reported by Suzuki et al provide the most valid estimates for D-dimer sensitivity and specificity; however, the relatively small sample size (N=220) resulted in imprecise estimates, with a lower limit of the 95% confidence interval (CI) of 0.90 for sensitivity and 0.38 for specificity.


--A conservative estimate based on these results indicates that the negative likelihood ratio for D-dimer is approximately 0.2 and the positive likelihood ratio is 1.5. If these approximations are validated in a larger prospective study, a positive D-dimer result would have no value in clinical decisionmaking, but a negative D-dimer result may decrease the probability of aortic dissection to a moderate degree.


--However, to rule out aortic dissection with a negative D-dimer result, the pretest probability would have to be very low. 


--Unfortunately, unlike pulmonary embolism or acute myocardial infarction, there are no validated clinical prediction rules to aid clinicians with establishing a pretest probability of aortic dissection.

BOTTOM LINE:

--studies used d-dimer cutoff of 500ng/ml

--high (but not perfect) sensitivity (90+%), low specificity

--potentially useful with patients with low pretest probability for aortic dissection

--since no validated prediction rules (like Wells/PERC for PE) for dissection, not quite ready for primetime

Submitted by J. Gullo.




Reference(s): PMID: 21478122; PMID: 21296332; PMID: 21546117; picture