Clotted blood tube (Serum gel separator clot activator tube)

Minimum blood volume: 5 mL

Paediatric clotted blood tube

Number of vials: 2

Minimum blood volume: 1.6 mL

After high dose methotrexate therapy, toxicity risk increases when serum methotrexate:

> 10 µmol/L at 24-hr

> 1.0 µmol/L at 48-hr

> 0.10 µmol/L at 72-hr

 (timed from start of methotrexate therapy)

(Source: from manufacturer's kit insert)

Monitoring levels of methotrexate to ensure appropriate therapy.

Serum methotrexate concentrations can vary widely depending on factors such as dosage, route of administration, and duration of infusion for different clinical indications; pharmacokinetic considerations, including hepatic and renal function; concurrent medications; and the patient’s clinical status.

Serum concentrations of methotrexate are commonly monitored during high-dose therapy (>50 mg/m2) to identify the time at which active intervention by leucovorin rescue should be initiated.

Limitations: Specimens from patients who received glucarpidase as a high dose methotrexate rescue therapy should not be tested with this methotrexate assay to avoid the reporting of falsely elevated methotrexate result due to assay interference.