Test Details
Methodology
Whole blood washing and red blood cell harvesting/counting. Liquid chromatography/tandem mass spectrometry (LC/MS-MS) after acidic hydrolysis.
Result Turnaround Time
6 - 12 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Use
This assay measures the red-cell concentration of 6-MMP (formed from 6-MP by thiopurine methyltransferase) and also measures the concentration of the resulting 6-TG after removal of the mono-, di-, or tri-phosphates from the various 6-thioguanine nucleotides. Once thiopurine therapy has been undertaken and an equilibrated drug level is achieved (usually three to six months), literature suggests that the measurement of thiopurine metabolites is warranted in the following situations:
1. Unresponsive patients to rule out (a) patient noncompliance (low 6-MMP and low 6-TG in those not taking medications), (b) those with diversion of metabolites away from 6-TG production (low 6-TG and normal or increased 6-MMP), (c) those with refractory to treatment (adequate 6-TG but lack of clinical response), and (d), those with excessive 6-MMP (or increased 6-MMP:6-TG ratio with adequate 6-TG) leading to increased hepatotoxicity.
2. Clinically responsive patients to look for excessive levels of either 6-MMP or 6-TG to avoid toxicity.
Limitations
This test should only be performed for patients currently on thiopurine therapy. This therapy includes administration of azathioprine or mercaptopurine. This test may not be useful in patients with autoimmune hepatitis.
Specimen Requirements
Specimen
Whole blood
Volume
3 mL
Minimum Volume
1 mL (Note: This volume does not allow for repeat testing.)
Container
Lavender-top (EDTA) tube
Collection Instructions
Collect blood in lavender-top (EDTA) tube only. Gently invert to mix. Submit whole blood refrigerated. Do not separate specimen. Do not freeze.
Stability Requirements
Temperature | Period |
|---|---|
Room temperature | 1 day |
Refrigerated | 8 days |
Frozen | unstable |
Reference Range
See table.
*Chevaux JB, Peyrin-Biroulet L, Sparrow MP. Optimizing thiopurine therapy in inflammatory bowel disease. Inflamm Bowel Dis. 2011 Jun; 17(6):1428-1435. | |
6-TGN | |
For treatment of inflammatory bowel disease (IBD)* | |
Suboptimal dosing | <235 pmol 6-TGN/8×108 red blood cells |
Optimal dosing | 235−450 pmol 6-TGN/8×108 red blood cells |
Increasing risk for myelotoxicity and leucopenia | >450 pmol 6-TGN/8×108 red blood cells |
6-MMPN | |
Hepatotoxicity risk | >5700 pmol 6-MMPN/8×108 red blood cells |
Storage Instructions
Refrigerate
Causes for Rejection
Frozen specimen; specimen not EDTA whole blood; gross hemolysis
LOINC® Map
| Order Code | Order Code Name | Order Loinc | Result Code | Result Code Name | UofM | Result LOINC |
|---|---|---|---|---|---|---|
| 503800 | Thiopurine Metabolites | 82869-9 | 503804 | 6-TGN | pmol/8x 10E8 | 32660-3 |
| 503800 | Thiopurine Metabolites | 82869-9 | 503806 | 6-MMPN | pmol/8x 10E8 | 32654-6 |
| Order Code | 503800 | |||||
| Order Code Name | Thiopurine Metabolites | |||||
| Order Loinc | 82869-9 | |||||
| Result Code | 503804 | |||||
| Result Code Name | 6-TGN | |||||
| UofM | pmol/8x 10E8 | |||||
| Result LOINC | 32660-3 | |||||
| Order Code | 503800 | |||||
| Order Code Name | Thiopurine Metabolites | |||||
| Order Loinc | 82869-9 | |||||
| Result Code | 503806 | |||||
| Result Code Name | 6-MMPN | |||||
| UofM | pmol/8x 10E8 | |||||
| Result LOINC | 32654-6 |
| Order Code | Order Name | Result Code | Result Name | UofM | Result LOINC | |
|---|---|---|---|---|---|---|
| Reflex 1 | 504035 | Serial Monitoring | 000000 | Serial Monitoring | N/A | |
| Reflex 1 | ||||||
| Order Code | 504035 | |||||
| Order Name | Serial Monitoring | |||||
| Result Code | 000000 | |||||
| Result Name | Serial Monitoring | |||||
| UofM | ||||||
| Result LOINC | N/A | |||||
| Order Code | Order Name | Result Code | Result Name | UofM | Result LOINC | |
|---|---|---|---|---|---|---|
| Reflex 1 | 504035 | Serial Monitoring | 511958 | 80563-0 | ||
| Reflex 1 | ||||||
| Order Code | 504035 | |||||
| Order Name | Serial Monitoring | |||||
| Result Code | 511958 | |||||
| Result Name | ||||||
| UofM | ||||||
| Result LOINC | 80563-0 | |||||