Turnaround times
The quoted turnaround time is from sample receipt in the laboratory, to results authorisation in the Laboratory Information Management system. The times do not include transport of specimen to the laboratory or the administrative process to print and post/email reports. Service users must allow for transport and reporting time when ordering tests.
Clinical background:
The immunosuppressive effect of thiopurine drugs (like azathioprine) is mediated primarily by the cytotoxic metabolite 6TGN, and incorporation of these false bases into DNA. Accumulation of high levels of 6TGN is also responsible for some side effects of thiopurine drugs and has been associated with leucopaenia.
Measurement of 6MMPN helps to distinguish patients who are underdosed or non-compliant (6-MMPN levels appropriately low) from those demonstrating resistance to thiopurine drugs, i.e. preferentially metabolising thiopurine drugs to inactive 6MMPN rather than 6-TGN (6-MMPN disproportionately increased).
In resistant patients, increasing the azathiopurine dose is not helpful and further increases 6-MMPN levels, predisposing to hepatotoxicity.
Specimen container paediatric:
Whole blood, Pink – EDTA
Specimen container adult:
Whole blood, Purple – EDTA
Minimum volume paediatric:
4 mL
Minimum volume adult:
4 mL
Special requirements:
A pre-dose (trough) sample is recommended
Sample stability:
- 3 days at room temperature
- 7 days refrigerated
Transport requirements:
Ambient temperature
Quality Assurance:
UK NEQAS
Reference ranges:
- TGN: 235 – 450 pmol/8×10^8 RBCs – Maximum drug efficacy.
- 6MMPN: >5700 pmol/8×10^8 RBCs – increased risk of hepatoxicity.
Other Info:
Referral Laboratory: Specialist Chemistry, Postal Reception, Pathology Department, Sandwell General Hospital, Lyndon, West Bromwich B71 4HJ