Laboratory Section - Laboratory Tests for Heart Transplant Rejection

IMPORTANT REMINDER

This Medical Policy has been developed through consideration of medical necessity, generally accepted standards of medical practice, and review of medical literature and government approval status.

Benefit determinations should be based in all cases on the applicable contract language. To the extent there are any conflicts between these guidelines and the contract language, the contract language will control.

The purpose of medical policy is to provide a guide to coverage. Medical Policy is not intended to dictate to providers how to practice medicine. Providers are expected to exercise their medical judgment in providing the most appropriate care.

Description

After heart transplantation, patients are monitored for cellular rejection by endomyocardial biopsies that are typically obtained from the right ventricle on a weekly basis for the first month, monthly for the following six months and yearly thereafter. Endomyocardial biopsy is invasive and carries significant risk of adverse effects. Therefore, noninvasive methods of detecting cellular rejection have been explored.  Two less invasive techniques are now commercially available for the detection of heart transplant rejection.

The first technique is based on the understanding that in heart transplant recipients, oxidative stress appears to accompany allograft rejection that degrades membrane polyunsaturated fatty acids and evolving alkanes and methylalkanes, which are in turn excreted as volatile organic compounds in breath.  The Heartsbreath test (Menssana Research, Inc) is a noninvasive test, measuring breath markers of oxidative stress, that has been developed to assist in the detection of heart transplant rejection. The Heartsbreath test analyzes the breath methylated alkane contour (BMAC), which is derived from the abundance of C4-C20 alkanes and monomethylalkanes and has been identified as a marker to detect grade 3 (significant) heart transplant rejection.

The Heartsbreath test received approval from the U.S. Food and Drug Administration (FDA) through a humanitarian device exemption in February 2004. The Heartsbreath test is indicated for use as an aid in the diagnosis of grade 3 heart transplant rejection in patients who have received heart transplants within the preceding year. The device is intended to be used as an adjunct to, and not as a substitute for, endomyocardial biopsy and is also limited to patients who have had endomyocardial biopsy within the previous month.

Another approach focuses on patterns of gene expression of immunomodulatory cells as detected in the peripheral blood. For example, microarray technology permits the analysis of the gene expression of thousands of genes, including those with functions that are known or unknown. Patterns of gene expression can then be correlated with known clinical conditions, permitting a selection of a finite number of genes to compose a custom multi-gene test panel, which can then be evaluated using polymerase chain reaction (PCR) techniques.  AlloMap™ is a commercially available molecular expression test that has been developed to detect acute heart transplant rejection or the development of graft dysfunction. FDA has recently granted 510k clearance for this test. The test involves PCR expression measurement of a panel of genes derived from peripheral blood cells, and applies an algorithm to the results. The algorithm produces a single score that considers the contribution of each gene in the panel.

Policy/Criteria

1. The measurement of volatile organic compounds with the Heartsbreath test to assist in the detection of grade 3 heart transplant rejection is considered investigational.
2. The evaluation of genetic expression in the peripheral blood for the detection of acute heart transplant rejection or graft dysfunction is considered investigational.

Scientific Background

Heartsbreath Test

The FDA approval of the Heartsbreath test was based on the results of the National Heart Lung and Blood Institute sponsored study entitled Heart Allograft Rejection: Detection with Breath Alkanes in Low Levels (the HARDBALL study). (2) The HARDBALL study was a three-year multicenter study of 1,061 breath samples in 539 heart transplant patients. Prior to scheduled endomyocardial biopsy, patient breath was analyzed by gas chromatography and mass spectroscopy for volatile organic compounds. The amount of C4-C20 alkanes and monomethylalkanes was used to derive the marker for rejection known as the BMAC. The BMAC results were compared with subsequent biopsy results as interpreted by two readers using the International Society for Heart and Lung Transplantation (ISHLT) biopsy grading system as the "gold standard" for rejection.

The authors of the HARDBALL study reported the abundance of breath markers of oxidative stress were significantly greater in grade 0, 1 or 2 rejection than in healthy normal subjects. However, in grade 3 rejection, the abundance of breath markers of oxidative stress was reduced, most likely due to accelerated catabolism of alkanes and methylalkanes that comprise the BMAC. The authors also reported finding that in identifying grade 3 rejection, the negative predictive value of the breath test (97.2%) was similar to endomyocardial biopsy (96.7%), and that the breath test could potentially reduce the total number of biopsies performed to assess for rejection in patients at low risk for grade 3 rejection. The sensitivity of the breath test was 78.6% vs. 42.4% with biopsy. However, the breath test had lower specificity (62.4%) and a lower positive predictive value (5.6%) in assessing grade 3 rejection than biopsy (specificity 97%, positive predictive value 45.2%). Additionally, the breath test was not evaluated in grade 4 rejection.

AlloMap™ Test

Patterns of gene expression were studied in the Cardiac Allograft Rejection Gene Expression Observation Study (CARGO) study, which included eight U.S. cardiac transplant centers enrolling 650 cardiac transplant recipients, encompassing over 5,000 clinical encounters. Patient blood samples were obtained at the time of endomyocardial biopsy, and the expression levels of over 7,000 genes known to be involved in immune responses were assayed and compared to the biopsy results. A subset of 200 candidate genes were identified that showed promise as markers that could distinguish transplant rejection from quiescence, and from there, a panel of 20 genes was selected that could be evaluated using PCR assays.  A proprietary algorithm is applied to the results of the analysis, producing a single score that considers the contribution of each gene in the panel. The third phase in the development of the AlloMap™ test was a pivotal validation study designed to further evaluate the algorithm and establish performance characteristics of the test. This phase of the study, which enrolled 270 patients, was prospective and blinded.

Results of the CARGO study presented at the 2005 annual meeting of the International Society of Heart Lung Transplantation and published in 2006. (3-7) Primary validation was conducted using samples from 63 patients independent from discovery phases of the study and enriched for biopsy-proven evidence of rejection. A prospectively defined test cutoff value of 20 resulted in correct classification of 84% of patients with moderate/severe rejection but just 38% of patients without rejection. Of note, in the “training set” used in the study, these rates were 80% and 59%, respectively. The authors evaluated the 11-gene expression profile on 281 samples collected at 1 year or more from 166 patients’ representative of the expected distribution of rejection in the target population (and not involved in discovery or validation phases of the study). When a test cutoff of 30 was used, the negative predictive value (no moderate/severe rejection) was 99.6%; however, only 3.2% of specimens had grade 3 or higher rejection. In this population, grade 1B scores were found to be significantly higher than grade 0, 1A, and 2 scores but similar to grade 3 scores. The sensitivity and specificity for determining quiescent versus early stages of rejection was not addressed.

Post-CARGO clinical observations have also been published. (8) The multicenter work group identified a number of factors that can affect AlloMap scores, including the time post-transplant, corticosteroid dosing, and transplant vasculopathy. (8, 9) Scores of 34 and above were considered positive, potentially indicating rejection, whereas scores below that threshold were considered negative with no evidence of rejection. Analysis of data from a number of centers collected post-CARGO showed that, at 1 year or more post-transplantation, an AlloMap threshold of 34 had a positive predictive value (PPV) of 7.8% for scores of >/= 3A/2R on biopsy and a negative predictive value of 100% for AlloMap scores below 34. These findings are limited due to a very low number of events; only 5 biopsy samples (2.4%) were found to have a grade of 2R or greater. At 1 year, 28% of the sample showed an elevated AlloMap score (>34) even though there was absence of evidence of rejection on biopsy. The significance of chronically elevated AlloMap scores in the absence of clinical manifestation of graft dysfunction and the actual impact on the number of biopsies performed is currently unknown.

Evans and colleagues discussed the economic implications of noninvasive testing for cardiac allograft rejection, based on the assumption that a positive AlloMap™ test would result in a confirmatory biopsy, while a negative test would permit deferral of a biopsy. (10) Based on the results of the CARGO study, the authors estimate that during the first post-transplant year, the numbers of endomyocardial biopsies would be halved, resulting in an aggregate cost savings for all heart transplant patients of 12 million dollars per year.

A review from the California Technology Assessment Forum concluded that given the post-hoc change in the threshold and the small size of the CARGO primary validation study (reviewed above), “it would be prudent to require independent confirmation of the CARGO study results” before widespread adoption of AlloMap gene expression profiling to monitor heart transplant patients occurs. (11) This 2006 Technology Assessment also noted that there were no studies that compared clinical outcomes of patients monitored with gene expression profiling to those of patients monitored with endomyocardial biopsies. Some of these issues will be addressed by an ongoing randomized clinical trial (IMAGE) comparing AlloMap molecular testing with traditional biopsy based surveillance for heart transplant rejection. The IMAGE trial began recruiting subjects in January 2005. The design and objectives of the IMAGE trial have been reported; no results are available at this time. (12)

Summary

While endomyocardial biopsy is the gold standard for assessing heart transplant rejection, biopsy may be limited by a high degree of interobserver variability in grading of results and the significant morbidity, and even mortality, that can occur with the biopsy procedure. Additionally, the severity of rejection may not always coincide with the grading of the rejection by biopsy. Finally, biopsy cannot be used to identify patients at risk of rejection, limiting the ability to initiate therapy to interrupt the development of rejection. For these reasons, endomyocardial biopsy is considered a flawed gold standard by many. Therefore, it is hoped that both Heartsbreath and AlloMap™ will assist in determining appropriate patient management and avoid over or under use of treatment with steroids and other immunosuppressants that can occur with false negative and false positive biopsy reports.

Additional clinical experience is needed to confirm and extend the current results, and to address several important questions such as the best cutoff value and when to test. Furthermore, the impact of this test on management decisions and health outcomes is unknown. Frequent monitoring with AlloMap could potentially result in an increase in the number of biopsies performed in stable patients who would not otherwise undergo routine biopsy. Evidence to date is insufficient to permit conclusions concerning the effect of the technology on health outcomes. Therefore, routine use of gene expressionprofiling in post-transplantation surveillance is considered investigational.

References

1. BlueCross BlueShield Medical Policy Reference Manual, Policy No. 2.01.68.
2. Phillips M, Boehmer JP, Cataneo RN, et al. Heart allograft rejection: detection with breath alkanes in low levels (the HARDBALL study). J Heart Lung Transplant 2004;23(6):701-8
3. Bernstein D, Mital S, Addonizio L et al. Gene expression profiling of cardiac allograft recipients with mild acute cellular rejection. J Heart Lung Transplant  2005;24(2 suppl):S65
4. Eisen HJ, Den MC, Klinger TM et al. Longitudinal monitoring of cardiac allograft recipients using peripheral blood gene expression profiling: a retrospective observational analysis of molecular testing in 19 case studies. J Heart Lung Transplant  2005;24(2 suppl):S162
5. Starling RC, Deng MC, Kobashigawa JA et al.  The influence of corticosteroids on the alloimmune molecular signature or cardiac allograft rejection. J Heart Lung Transplant 2005;24(2 suppl):S65-S66
6. Marboe CC, Lal PG, Chu K et al. Distinctive peripheral blood gene expression profiles in patients forming nodular endocardial infiltrates (Quilty lesions) following heart transplantation. J Heart Lung Transplant 2005;24(2 suppl):S97
7. Deng MC, Eisen HJ, Mehra MR et al. Noninvasive discrimination of rejection in cardiac allograft recipients using gene expression profiling.  Am J Transplant 2006;6(1):150-60
8. Starling RC, Pham M, Valantine H et al; Working Group on Molecular Testing in CardiacTransplantation. Molecular testing in the management of cardiac transplant recipients: initial clinical experience. J Heart Lung Transplant 2006; 25(12):1389-95
9. Yamani MH, Taylor DO, Rodriguez ER et al. Transplant vasculopathy is associated with increased AlloMap gene expression score. J Heart Lung Transplant 2007; 26(4):403-6
10. Evans RW, Williams GE, Baron HM. The economic implications of noninvasive molecular testing for cardiac allograft rejection. Am J Transplant 2006; 5(6):1553-8
11. California Technology Assessment Forum. Gene expression profiling for the diagnosis of heart transplant rejection. San Francisco, CA: 2006. Available online at http://www.ctaf.org/content/general/detail/624. (Verified 08/26/08)
12. Pham MX, Deng MC, Kfoury AG et al. Molecular testing for long-term rejection surveillance in heart transplant recipients: design of the Invasive Monitoring Attenuation Through Gene Expression(IMAGE) trial. J Heart Lung Transplant 2007; 26(8):808-14

Cross References

None

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