Biochemistry Lab

Hi All,

On the second and third week of my attachment in a Clinical Biochemistry lab, I was stationed at the TDX station to observe how blood levels of therapeutic drugs are tested.

For this week's post, I'm zooming in to one of the most commonly tested drug - Cyclosprine A.

Cyclosporine A is an immunosuppressive drug which is used to combat tissue rejection following organ transplantation. For example, after an organ (liver, kidney, skin etc) transplant, the immune system of the recipient may reject the introduction of a foreign tissue. T cells and other immune cells may be induced to destroy the foreign cells, leading to graft rejection. Cyclosporine A is thus administered to enable graft survival by reducing the activity of the recipient’s immune system.

Cyclosporine A has a narrow TI (Therapeutic Index) and is also associated with nephrontoxicity and hepatotoxcity, it is therefore recommended to have regular drug monitoring for the patients on this medication. (This explains why I notice a handful of repeated names everyday.)

Procedure

The specimens, which are whole blood specimens received in EDTA tubes, are labeled with a specific bar code that gives each specimen a code number.

1. Microcentrifuge tubes are labeled with patient’s code number. Control tubes are labeled with L (low), M (medium) and H (high).
   
2. Control reagents are provided and treated in the same way as a patient’s sample.
   
3. The samples are mixed by gentle inversion and 150ul of the sample are accurately pipetted into the labeled mircocentrifuge tubes accordingly. (During pipetting, it is important to make sure that blood do not stick to outside of the pipette tips as this would cause additional volume to be added to microcentrifuge tube)
   
4. 50ul of solubilization reagent and 300ul of whole blood precipitation reagent are pipetted into each mircocentrifuge tube.
   
5. After pipetting all the samples, each tube are capped securely and vortex for a full 10 seconds to ensure thorough mixing. After which, samples are centrifuged for 5 minutes at 10900rpm. A clear supernatant and a hard, compact pellet of denatured proteins would be obtained after centrifugation.
   
6. The supernatant of each specimen is decanted completely into the sample well of a sample cartridge. The cartridges are then positioned on a carousel and are ready to be placed into the TDX machine.


7. Other than the carousel, a reagent pack is also placed in the TDX machine. This reagent pack should be mixed by gentle inversion and bubbles should be removed prior to placing the pack on the reagent platform in the TDX.


8. When both carousel and reagent pack are placed stably on their respective platforms, the cover is closed and the analyzer would begin upon pressing RUN, ASSAY 50.


9. Allow time for the machine to operate and once the results are produced, the control values are matched to ensure it falls within the acceptable range. If it does, patient’s results are accepted. If it does not, a rerun of the test is required.

Tan Zhao Rong

TG01