Metals, toxins and medication
Sirolimus
The sirolimus level checks the dosage in people who take this immunosuppressive medicine after a transplant.
Everything about this testWhat it measures
The analysis measures how much sirolimus is in your blood. Sirolimus, also known as rapamycin, suppresses the immune system and is mainly used to prevent rejection of a transplanted kidney; it is also used for a few rare conditions. The measurement is done in whole blood, because sirolimus is mostly found in the red blood cells. It is a trough level: blood taken just before the next dose.
- Whether the sirolimus dosage is in the range the treating doctor wants in someone who uses this medicine
- A level that is too low, with a greater risk of rejection of a transplanted organ
- A level that is too high, with a greater risk of side effects
High
A level that is too high gives a greater chance of side effects of sirolimus, including blood count abnormalities, raised fats in the blood, fluid retention and poorer wound healing. Stronger suppression of the immune system, and therefore a greater chance of infections, is also part of this. Which level is too high depends on the type of transplant, the time since the transplant and the other medicines; the treating doctor assesses this.
Low
A level that is too low means that the immune system is suppressed less than intended, with a greater chance of rejection of the transplanted organ. A low value can be caused by too low a dosage, a missed dose, an interaction with another medicine or poor absorption. In someone who does not use sirolimus, no sirolimus can be detected in the blood; this is expected and means nothing.
Preparation
- Have your blood taken just before your next dose of sirolimus and take that dose only after the sample is taken.
If your result is abnormal
The treating doctor adjusts the dosage based on the level and repeats the measurement, more often after a change in dosage or medication. If there are signs of rejection or serious side effects, an assessment at the transplant center follows.
Reliability
Sirolimus is dosed based on the blood level, because the amount in the blood at the same dose differs greatly from person to person. The measurement can only be interpreted as a trough level, just before the next dose, and in relation to the other immunosuppressive medicines. In someone who does not use sirolimus, the result has no meaning.
Limitations
- Only a trough level just before the next dose can be compared with the target values; at any other time the result is not usable.
- Sirolimus is broken down in the liver through a pathway that many medicines affect; certain antibiotics, antifungals, antiepileptics and grapefruit juice, among others, change the level.
- The measurement is done in whole blood; a result from serum or plasma is not comparable.
- Laboratories use different methods, so results can differ between laboratories.
How common is this
In the Netherlands, about a thousand kidney transplants take place each year, in addition to transplants of other organs. Everyone with a transplanted organ uses immunosuppressive medicines; sirolimus is one of the less commonly used of these.
Who is this useful for
This is not a preventive test. The test is intended for people who use sirolimus; the treating doctor in the hospital orders the level and assesses it. For people who do not use the medicine, the measurement has no meaning.
Downsides and risks
- A measurement at the wrong time or in the wrong tube gives a result that cannot be interpreted and can lead to a wrong dose adjustment.
- A level measured outside the treatment team lacks the context of the other medicines and the time since the transplant.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results