At a Glance
Why Get Tested?
To determine the level of sirolimus in the blood in order to establish a dosing regimen, maintain therapeutic levels, and detect toxic levels
When to Get Tested?
As soon as sirolimus therapy begins and whenever dose is changed; frequently at first, then at regular intervals to monitor concentrations over time; whenever excess or deficient levels are suspected
A blood sample drawn from a vein in your arm
Test Preparation Needed?
Have the sample collected 12 hours after the last dose and immediately prior to the next dose, or as directed by your doctor
The Test Sample
What is being tested?
This test measures the amount of sirolimus in the blood. Sirolimus is a relatively new drug that is used to suppress the immune system in people who have had an organ transplant. Normally, a person's immune system recognizes a transplanted organ as foreign and begins to attack it. Sirolimus limits this response and helps to prevent organ rejection by inhibiting the activation and production of white blood cells called T-lymphocytes. It also inhibits antibody production.
Sirolimus is typically taken by mouth (orally) and, after ingestion, is absorbed from the digestive tract. The concentration peaks in the blood within a couple of hours and then gradually declines. It is metabolized by the liver and is eliminated from the body in the stool (more than 90%) and urine (less than 2%).
The U.S. Food and Drug Administration (FDA) has currently approved sirolimus for use in people 13 years of age and older who have kidney transplants. It appears to be less toxic to the kidneys than other options and can be given in conjunction with the other immunosuppressant drugs cyclosporine and tacrolimus. Studies to evaluate its use in other age groups and types of organ transplantation, such as liver or lung, are ongoing. Like other immunosuppressant agents, sirolimus may cause side effects and adverse reactions and is associated with an increased risk of infection and the development of lymphoma.
The sirolimus level must be monitored over time with laboratory tests because the drug has a narrow therapeutic index or range of effective concentration. If the drug concentration is too low, organ rejection may occur; if it is too high, symptoms associated with toxicity may develop. The sirolimus blood test is usually measured as a "trough" level, with blood collection just prior to the next dose – at the drug's lowest concentration in the blood.
Typically, sirolimus is given with cyclosporine and corticosteroids. Dosages must be tailored to the individual, and sirolimus and cyclosporine must both be monitored. Often, people will begin with a loading dose of sirolimus and then tapered to a lower dose. In people considered at low risk for complications, cyclosporine may be decreased after 2-4 months and sirolimus concentrations increased.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
Have the sample collected 12 hours after the last dose and immediately prior to the next dose, or as directed by your doctor.
Ask a Laboratory Scientist
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NOTE: This article is based on research that utilizes the sources cited here as well as the collective experience of the Lab Tests Online Editorial Review Board. This article is periodically reviewed by the Editorial Board and may be updated as a result of the review. Any new sources cited will be added to the list and distinguished from the original sources used.
Sources Used in Current Review
(October 10, 2003) Transplant Living: Sirolimus. Available online through http://www.transplantliving.org. Accessed July 2011.
(July 14, 2009) U.S. Food and Drug Administration. Information for Healthcare Professionals: Immunosuppressant Drugs: Required Labeling Changes. Available online through http://www.fda.gov/. Accessed July 2011.
Food and Drug Administration. Prescribing Information (Approval 1999). PDF available for download at http://www.accessdata.fda.gov/drugsatfda_docs/label/2008/021083s033,021110s043lbl.pdf through http://www.accessdata.fda.gov. Accessed July 2011.
(©2011) Cleveland Clinic. Transplant programs: Sirolimus. Available online at http://my.clevelandclinic.org/transplant/services/kidney/sirolimus.aspx through http://my.clevelandclinic.org. Accessed July 2011.
(©2011) eMedicine Health. Drugs and Medications, Rapamune. Available online at http://www.emedicinehealth.com/drug-sirolimus/article_em.htm through http://www.emedicinehealth.com. Accessed July 2011.
Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC. Pg 462.
Tietz Textbook of Clinical Chemistry and Molecular Diagnostics. 4th ed., Burtis CA and Ashwood ER, eds. Philadelphia: W. B. Saunders Company; 2005. Pp 1278-1280.
(2010 February 10, Revised) MedlinePlus Drug InformationSirolimus [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a602026.html. Accessed July 2011.
(2007 March) National Diabetes Information Clearinghouse. Pancreatic Islet Transplantation [On-line information]. Available online at http://diabetes.niddk.nih.gov/dm/pubs/pancreaticislet/ through http://diabetes.niddk.nih.gov. Accessed July 2011.
Van de Beek, D et al. No Major Neurologic Complications With Sirolimus Use in Heart Transplant Recipients. Mayo Clinic Proceedings April 2009 vol. 84 no. 4 330-332. Available online at http://www.mayoclinicproceedings.com/content/84/4/330.full through http://www.mayoclinicproceedings.com. Accessed July 2011.
Sources Used in Previous Reviews
Clarke, W. and Dufour, D. R., Editors (2006). Contemporary Practice in Clinical Chemistry, AACC Press, Washington, DC. Pp 462.
Wu, A. (2006). Tietz Clinical Guide to Laboratory Tests, Fourth Edition. Saunders Elsevier, St. Louis, Missouri. Pp 1482-1485.
Buck, M. (2006 March 13). Immunosuppression with Sirolimus after Solid Organ Transplantation in Children [24 paragraphs]. Medscape from Pediatr Pharm 2006;12(2) [On-line information]. Available online at http://www.medscape.com/viewarticle/524753_1 through http://www.medscape.com. Accessed 11/2/07.
Aradhye, S et. al. (2006 December, Revised). Medicines for Keeping Your New Kidney Healthy. American Society of Transplantation [On-line information]. PDF available for download through http://www.a-s-t.org. Accessed 11/4/07.
American Society of Health-System Pharmacists, Inc. (2004 January, Revised). Sirolimus. AHFS [On-line information]. Available online at http://www.ashp.org/mngrphs/ahfs/a300009.htm through http://www.ashp.org. Accessed 11/2/07.
(2003 January 01, Revised). Sirolimus. MedlinePlus Drug Information [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/druginfo/medmaster/a602026.html. Accessed 11/1/07.
(2007 September 13). Drug-Coated Stents Go Head to Head. MedlinePlus Health Day [On-line information]. Available online at http://www.nlm.nih.gov/medlineplus/news/fullstory_54789.html through http://www.nlm.nih.gov. Accessed 11/1/07.
(2007 March). Pancreatic Islet Transplantation. National Diabetes Information Clearinghouse [On-line information]. Available online at http://diabetes.niddk.nih.gov/dm/pubs/pancreaticislet/ through http://diabetes.niddk.nih.gov. Accessed 11/1/07.
Lexi-Comp (2007 June, Revised). Sirolimus. Merck Manual Professional [On-line information]. Available online at http://www.merck.com/mmpe/lexicomp/sirolimus.html through http://www.merck.com. Accessed 11/2/07.
(© 2007). Sirolimus. ARUPs Laboratory Test Directory [On-line information]. Available online at http://www.aruplab.com/guides/ug/tests/0098467.jsp through http://www.aruplab.com. Accessed 11/1/07.
(© 2007). Sirolimus (Rapamune ®), Blood. Labcorp Test Directory [On-line information]. Available online at http://www.labcorp.com/datasets/labcorp/html/chapter/ through http://www.labcorp.com. Accessed 11/1/07.
(© 2007). Sirolimus (Rapamycin). Quest Diagnostics Test Menu [On-line information]. Available online through http://cas2.questdiagnostics.com. Accessed 11/2/07.
(© 2007). Sirolimus MonitR. Specialty Laboratories Test Menu [On-line information]. Available online at http://www.specialtylabs.com/tests/details.asp?id=4940 through http://www.specialtylabs.com. Accessed 11/2/07.