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Communications to the Editor |

Screening in Hereditary Hemorrhagic Telangiectasia Patients FREE TO VIEW

Marie E. Faughnan, MD; Robert H. Hyland, MD, FCCP; Kumar Nanthakumar, MD; Donald A. Redelmeier, MD
Author and Funding Information

Affiliations: University of Toronto Toronto, Canada,  Odense, Denmark

Correspondence to: Robert H. Hyland, MD, FCCP, St Michael’s Hospital, Department of Medicine, 30 Bond St, Toronto, Ontario, Canada M5B 1W8; e-mail: hylandb@smh.toronto.on.ca



Chest. 2000;118(2):566-567. doi:10.1378/chest.118.2.566-a
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To the Editor:

We read with great interest the article by Kjeldsen et al in CHEST (August 1999)1 regarding screening for pulmonary arteriovenous malformations (PAVMs). It attempts to address one of the important issues in caring for people with hereditary hemorrhagic telangiectasia: the approach to screening for PAVMs. However, it falls short on several counts.

This article evaluated the performance of pulse oximetry (supine and upright), as well as Pao2 on room air and 100% oxygen, in patients with right to left shunt on contrast echocardiography. The authors assumed the sensitivity of contrast echocardiography to be 100%, despite the lack of published data on the sensitivity of contrast echocardiography for detecting intrapulmonary shunt. We have published, in abstract form,2 results to indicate that though contrast echocardiography is a useful screening tool, it is clearly not 100% sensitive. Although the study was designed to evaluate the performance of various screening tests in a group of patients with positive contrast echocardiography, the authors concluded that the strategy of initial contrast echocardiography followed by 100% oxygen is the best strategy. Since the population of contrast-negative patients was not evaluated, they cannot draw conclusions about the performance of this screening strategy.

Our second concern involves their interpretation of the Pao2 on 100% oxygen. Our own experience has shown this to be a difficult test to perform reliably and that normal limits should be established using local results and a receiver operator characteristic curve. The authors have selected a cutoff point of 500 mm Hg without any justification. This is considerably lower than the theoretical normal cutoff. Since sensitivity of screening tests is so important in these patients, the justification of the cutoff point is essential.

Finally, the authors have reported sensitivity and specificity of the various screening tests despite the fact that the reference standard, pulmonary angiography, was not performed in all subjects. Only subjects who had positive contrast echocardiography underwent pulmonary angiography. This is not the conventional method for reporting sensitivity and specificity and leads to an overestimation of sensitivity and an underestimation of specificity.

We are left with the important question as to whether or not contrast echocardiography alone is adequate screening.

References

Kjeldsen, AD, Oxhoj, H, Andersen, PE, et al (1999) Pulmonary arteriovenous malformations: screening procedures and pulmonary angiography in patients with hereditary hemorrhagic telangiectasia.Chest116,432-439
 
Nanthakumar, K, Faughnan, ME, Graham, AT, et al Screening for pulmonary arteriovenous malformations using contrast echocardiography in hereditary hemorrhagic telangiectasia [abstract]. J Am Soc Echocardiogr. 1999;;12 ,.:408
 
To the Editor:

So far, the major concern of using contrast echocardiography (CE) as a screening tool has been that the procedure may be too sensitive, producing too many false-positive results. Faughnan et al found 1 false-negative study out of 14. However, their CE procedure is different from ours, which may explain their findings.

We did not experience any problems performing 100% oxygen studies, but a qualified well-educated staff is essential while the test is performed. Our reasons for selecting 500 mm Hg as cutoff are explained on page 435 of our article.

We agree with Faughnan et al that it is still not known whether CE alone is adequate for screening. As we have explained in our article, we do not agree that pulmonary angiography is the reference standard for diagnosing pulmonary arteriovenous malformation (PAVM). The task in screening for PAVM is to use a highly sensitive procedure to exclude those patients who are not at risk from undergoing further and more invasive procedures.


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References

Kjeldsen, AD, Oxhoj, H, Andersen, PE, et al (1999) Pulmonary arteriovenous malformations: screening procedures and pulmonary angiography in patients with hereditary hemorrhagic telangiectasia.Chest116,432-439
 
Nanthakumar, K, Faughnan, ME, Graham, AT, et al Screening for pulmonary arteriovenous malformations using contrast echocardiography in hereditary hemorrhagic telangiectasia [abstract]. J Am Soc Echocardiogr. 1999;;12 ,.:408
 
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