The AlloMap Testing Process
Sample collection and preparation
The AlloMap® test requires a blood sample obtained by routine phlebotomy and additional processing steps that enable the extraction and stabilization of RNA from peripheral blood mononuclear cells (PBMCs). After blood is collected, it is centrifuged to isolate the PBMCs. Further processing of the PBMCs releases the RNA from the cells and preserves it to ensure the recovery of high quality RNA for testing. The preserved sample is shipped together with the completed test requisition form to the clinical laboratory at CareDx.
AlloMap testing process at the Clinical Laboratory at CareDx
The testing procedure involves sequential steps beginning with purification of RNA from the sample received and finishing with the reporting of the AlloMap test score to the clinician. The clinical laboratory at CareDx® has optimized and standardized the performance of the AlloMap test processes. Comprehensive quality control ensures the reliability of the gene expression measurements used in the calculation of the AlloMap test score.
After purification, RNA is reverse transcribed into complementary DNA (cDNA), which is added to each of 60 wells containing gene-specific primers and probes. The expression of each gene is then measured by amplification and fluorescence detection using instruments that are configured for standard quantitative real-time polymerase chain reaction (qRT-PCR).
Quality control and normalization
The relative expression of the quality control genes used in AlloMap testing provides the data to assess the quality of all of the testing process. These include:
- Gene-specific measurement ranges
- Efficiency of the qRT-PCR
- Accuracy and consistency
Generation of the AlloMap Test Score
A proprietary mathematical algorithm combines the measured expression values for each gene into a single integer value between 0 and 40 that is reported as the AlloMap test score. The clinician uses this score in the overall assessment of the probability of rejection at the time of testing.
The clinical laboratory at CareDx reports the AlloMap test score to the ordering physician within 1 to 2 business days after receipt of the sample at its Brisbane, CA facility. Upon receipt of the test report from CareDx by fax, the physician interprets the report as part of the patient’s overall clinical assessment.
The blood sample is prepared and sent via overnight courier to the clinical laboratory at CareDx in Brisbane, California.
In most cases, the blood sample is shipped to CareDx on the same day as your patient's lab. The sample generally arrives at the clinical laboratory at CareDx the next morning.
Once the blood sample arrives, complex gene expression information is extracted and analyzed.
Gene expression information is translated into clinically actionable information and reported to the clinician within 1 to 2 days after blood sample is received.
The clinician uses the AlloMap score, along with other standard clinical assessments, to evaluate the patient's probability of rejection.