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PE in pregnancy: which diagnostic tests do you use?

Posted Mar 06 2013 12:00am


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Pulmonary embolism (PE) can be a deadly disease and one of the most challenging diagnosis to make in a pregnant patient. Patients may present with signs and symptoms that might also be present in a normal uncomplicated pregnancy. Even in nonpregnant patients, the diagnosis of venous thromboembolism (VTE) such as PE can be quite challenging. One challenge is that pregnant patients already have an increased risk of venous and arterial thromboembolism compared to nonpregnant patients due to the physiologic and structural changes during the intra- and postpartum period. Another challenge is that clinical decision aids such as Wells' criteria were not validated to rule out PE in pregnancy. This issue is problematic in the assessment of the pregnant patient whom some would consider, at least, to be at a moderate risk level for having PE. According to this retrospective chart review of 125 patients, a modified Wells' criteria was used retroactively to identify patients without PE via CT pulmonary angiogram (CTPA). From the patients identified the negative predictive value was 100% with a modified Wells' criteria <6 points (p≤0.001).


D-dimer

What about using a D-dimer test to risk-stratify? A BestBets review and a Stemlyns podcast addressed the question of using a negative D-dimer to rule out PE in pregnancy. The research performed by BestBets in 2004 and last modified in 2011 selected 5 studies out of 151 studies which addressed the question of interest. These studies had a small number of patients, and consisted of 2 prospective, a retrospective, a systematic review, and a case report study. Several studies showed normal elevation of D-dimers as pregnancy progressed, which is something that should be considered for future research on D-dimer cutoff values. 

BestBets’ conclusion (2011): There is NO current evidence to support the use of a single isolated negative D-dimer result to rule out PE in the pregnant patient.





Why don’t we just get a CTPA to rule-out all pregnant patients who may have a PE? 

Typically for non-pregnant patients, one starts the PE work up by obtaining a chest xray and determining a pre-test probability. Obtain a D-dimer for low pretest probability patients. If the D-dimer comes back elevated or if the pre-test probability is already moderate-high to start with, perform an imaging study such as a CTPA (or a V/Q scan). 

For pregnant patients, however, we just discussed that D-dimers aren't as helpful. Should we get a CTPA (or V/Q scan)? Such imaging studies place both the fetus and mother at risk for future malignancies. For this reason, if we order these tests, we should keep radiation exposure to “As Low As Reasonably Achievable” ( ALARA ) for both. We can provide a shield to protect the fetus and/or also place a urinary catheter to drain the radioactive isotope. Interestingly, the high cardiac output in pregnancy might not allow for appropriate vascular opacification in CTPA. Furthermore, the dye used in the V/Q scan has the potential of causing hypothyroidism in the unborn fetus. 

Using ultrasound

An alternative approach before obtaining a CTPA or V/Q scan is to start a PE workup with a chest x-ray and a lower extremity (LE) ultrasound to assess for deep venous thrombosis (DVT). If the LE ultrasound is positive, the treatment threshold is surpassed and the patient should be started on anticoagulants for a likely PE. If the ultrasound study shows no DVT, a more extensive work up involving irradiation (CTPA or V/Q scan) should now be considered in the decision process.


This still leaves many questions unanswered unfortunately...

Ultimately in the end, your clinical decision should be a multifactorial process, which considers the uncertainties of diagnostic findings, risk-benefit justification in obtaining or not obtaining a CTPA, patient's values, and your overall clinical judgment. 
Since there is no convincing literature on how to work up PEs for pregnant patients, I would love to hear comments on your thought process. 
  • Should we use elevated D-dimer cutoffs to rule out pulmonary embolism in pregnancy?
  • Would you skip D-dimers altogether since pregnant patients were excluded from the Wells derivation studies (making Wells scores not externally valid for pregnant patients)? Would you skip D-dimers altogether since pregnant patients are at greater baseline risk for VTE and thus automatically fall into the moderate-to- high risk category?  Do you start with a lower extremity ultrasound? Would you feel ok with a one time negative lower extremity ultrasound to rule out PE?
Comments?
Reference
Cutts, BA et al. New directions in the diagnosis and treatment of pulmonary embolism in pregnancy. Am J Obstet Gynecol. 2013 Feb;208(2):102-8. [PMID  22840412 ]

Heit, JA et al. Trends in the incidence of venous thromboembolism during pregnancy or postpartum: a 30-year population-based study. Ann Intern Med. 2005 Nov 15;143(10):697-706. [PMID 16287790 ]

James, AH. Venous Thromboembolism in Pregnancy. Arterioscler Thromb Vasc Biol. 2009 Mar;29(3):326-31. [PMID 19228606 ]

Le Gal G. et al. Diagnostic value of single complete compression ultrasonography in pregnant and postpartum women with suspected deep vein thrombosis: prospective study. BMJ. 2012 Apr 24;344:e2635. [PMID  22531869 ]

Shahir, K. et al. Pulmonary embolism in pregnancy: CT pulmonary angiography versus perfusion scanning. AJR Am J Roentgenol. 2010 Sep;195(3):W214-20. [PMID 20729418 ]


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