Mycophenolic Acid, Serum
Test Code
PGx MPA,S
CPT Codes
82491
Specimen
Blood serum
Volume
Spin down and send 2.0 mL of serum refrigerated.
Minimum Volume
2.0 mL
Container
Plain, red-top tube(s).
Storage Instructions
Refrigerate
Cause for Rejection
Serum gel tube is not acceptable; insufficient quantity.
Use
Mycophenolate mofetil (MMF), also known as Cellcept®, is a new immunosuppressive agent useful in organ transplantation medicine. In combination with either cyclosporin A (CsA) or tacrolimus and corticosteroid, MMF has been shown to reduce the incidence of acute rejection compared to azathioprine or placebo. This outcome is considered important in transplantation medicine since acute rejection is a major risk factor for the development of chronic graft rejection and graft loss. It is approved for use in renal transplant and under investigation for liver transplant. When mycophenolate mofetil enters the blood, it is immediately metabolized to the active drug, mycophenolic acid (MPA), which inhibits the enzyme inosine monophosphate dehydrogenase and interferes with the de novo pathway of guanosine nucleotide synthesis selectively in lymphocytes. MPA inhibits proliferative responses of T and B lymphocytes to both mitogenic and allospecific stimulation. MPA acts in the same fashion as azathioprine, and MPA is suggested as replacement therapy for azathioprine because it has fewer side effects. The drug is deactivated by hepatic phase II metabolism to form mycophenolic acid glucuronide (MPA-G).
At steady/state (5 days after therapy is initiated) on a typical one gram q.i.d. dose of MMF (Cellcept®), the trough serum level of mycophenolic acid ranges from 1-3.5 µg/mL. The MPA-G ranges from 35-100 µg/mL. Some patients who have low phase II hepatic conjugating capability may be overly immunosuppressed, resulting in a serum MPA trough level exceeding 4 µg/mL. The MPA-G level in such patients on the other hand is less than 35 µg/mL. Some patients have a high phase II metabolic capability; these patients may require doses in the range of 2-3 g q.i.d. to maintain trough serum MPA levels in the range of 1-3.5 µg/mL, and they are likely to have MPA-G levels > 120 µg/mL.
Methodology
High-Performance Liquid Chromatography (HPLC)
Turnaround Time
Five business days after receipt of specimen. STAT turnaround time of 3 business days is available for an additional charge.
