Frequently Asked Questions
1. On which analytical systems can I use the Saladax MyCare products?
The Saladax products can be used on a wide range of clinical chemistry analyzers. There are a number of different validated applications for various analyzers available and more are currently being developed. If you would like to know if the Saladax tests can be used on the clinical chemistry system used in your laboratory, please contact us for more information at firstname.lastname@example.org.
2. Whom can I contact when I have technical questions about the test?
For technical queries, please contact Saladax at email@example.com.
3. I am interested in using the Saladax products. How can I find my local representative?
Saladax has local representatives in Europe, Asia, the Middle East, Australia and the USA. Please send an e-mail to firstname.lastname@example.org and we will put you in contact with your local Saladax representative.
1. For which 5-FU-based treatment regimens can I use the My5-FU assay?
My5-FU can be used for all 5-FU continuous infusion regimens. Blood samples need to be drawn at 5-FU steady state in the bloodstream to calculate Area Under the Curve (AUC). Studies have been published most extensively on colorectal and head and neck cancer patients. Dose adjustment algorithms are found in the literature to guide doctors in adjusting the 5-FU dose to achieve target exposure. Patients on continuous 5-FU infusion for other solid tumors may be candidates for 5-FU dose management based on the doctor’s clinical experience and judgment.
2. Can I use 5-FU measurement to determine if a patient is DPD deficient?
There is evidence that a 5-FU test dose approach can be used to determine whether a patient is at risk of high toxicity, one contributing factor being DPD deficiency. Saladax is currently sponsoring a study to validate the 5-FU test dose protocol. For more information on this, please contact us at email@example.com.
3. Can the My5-FU test also be used for measuring capecitabine?
Capecitabine is an oral pro-drug that is enzymatically converted to 5-fluorouracil within the cell. 5-FU concentrations in the blood are different from tissue concentrations. In the blood, 5-FU concentrations of capecitabine patients are much lower than in those patients receiving continuous 5-FU infusion and studies to determine AUC target ranges for capecitabine are still outstanding. My 5-FU testing should therefore not be used for patients on capecitabine.
My5-FU Sample Collection & Handling
4. When is the best time to draw the blood sample for My5-FU measurement?
The best collection time for the 5-FU sample is at least 18 hours after the start of the infusion and before the pump runs empty. At this time 5-FU is at a steady-state concentration and the pump variability is lowest. While many patients may reach steady-state within two hours of the start of infusion, some patients takes longer to settle into steady-state and studies have shown that by 18 hours into the infusion all patients are at a steady-state 5-FU concentration.
5. Can I use the infusion port for the blood draw?
No, the infusion port cannot be used for sample collection. The 5-FU sample has to be taken at a peripheral port or by venous draw. Samples taken from the infusion port contain high concentrations of exogenous 5-FU and measured values would be falsely elevated. Flushing the port before taking the sample will not eliminate this risk and will not give an accurate 5-FU result.
6. How does the My5-FU Sample Stabilizer work?
5-FU is very instable in the whole blood. The Sample Stabilizer addresses this problem. It contains gimeracil, a uracil derivative. The molecule irreversibly inhibits DPD, the enzyme responsible for the breakdown of 5-FU in whole blood. When the stabilizer is added to the sample, gimeracil inhibits DPD activity and prevents 5-FU degradation. Once stabilized, samples can be stored at room temperature for up to 24 hours before centrifugation. Do not place the sample treated with sample stabilizer on ice, as this could cause falsely elevated 5-FU results.
7. I ran out of My5-FU Sample Stabilizer. Can I still draw blood for My5-FU measurement?
Yes, but 5-FU is instable in whole blood without the sample stabilizer and is rapidly degraded by DPD. To slow down DPD activity, the sample must be put on ice immediately after the draw and must be centrifuged within 1 hour of the draw if the stabilizer was not used.
8. There was a short draw during blood collection and I could only collect about 1.5 mL of blood. Can I still use the My5-FU Sample Stabilizer on this sample?
The recommended blood volumes for the sample stabilizer are 2-3 mL of blood. However, internal testing in the Saladax laboratory has shown that sample volumes between 1.5 and
10 mL can be used with the sample stabilizer.
9. The infusion pump ran empty later than scheduled. What time should I use for AUC calculation – the scheduled time or the actual infusion time?
Whenever possible, use the actual infusion time to calculate the AUC result, as this will give the most accurate AUC result. However, for simplicity, most people will use the standard time and not the actual time which will not make a substantive change in the dose adjustment.
10. What patient info should be recorded for accurate reporting of 5-FU results?
The minimum information required to calculate the AUC is the 5-FU infusion time and 5-FU concentration measured at steady state. However, we recommend recording the following patient information in addition:
- 5-FU infusion cycle
- Planned infusion time
- 5-FU concentration administered
- Start of infusion
- End of infusion
- Real infusion time
- Time of blood draw
- Was sample stabilizer added to the sample immediately after draw?
11. How do I transport the 5-FU samples from the oncology ward/local oncology practice to the laboratory?
After the sample has been centrifuged, the separated plasma can be shipped to the laboratory at room temperature. The sample should be processed within 7 days after the draw date.
12. What are the most common pre-analytical errors leading to erroneously low My5-FU results?
- Sample was not collected at steady state; for example when the infusion pump was already empty at sample draw.
- The tubing of the pump is kinked or the flow is obstructed.
- Sample stabilizer was not added to the sample immediately.
- Hemolysis. White blood cell contamination will break down 5-FU. If this happens, the patient sample must be redrawn.
13. What are the most common pre-analytical errors leading to erroneously high 5-FU results?
- Sample was drawn from the infusion port.
- Sample with sample stabilizer added was put on ice or in the refrigerator.
Sample Processing & Interpretation
14. What is the most relevant PK parameter for 5-FU?
The PK parameter most relevant for 5-FU is the AUC (area under the curve). The AUC can be calculated by multiplying the 5-FU concentration at steady state with the total infusion time.
Area under the curve [mg•hr/L] = Steady state concentration [mg/L] x Infusion time [hr]
15. Are there any cross-reactants for the My5-FU assay that I need to be aware of?
Theophylline, when tested at 10,000 ng/mL, showed a 4.6% cross reactivity in the My5-FU Assay. Samples from patients who have taken theophylline-containing drugs within 3 days before start of infusion should not be tested.
Theobromine, when tested at 20,000 ng/mL, had a cross-reactivity of 2.2%. To avoid any cross-reactivity of theobromine with the My5-FU assay, patients should not eat large amounts of chocolate 12 hours before and during the 5-FU infusion.
16. Can I measure lipemic, icteric or heamolytic samples?
With icteric and lipemic samples, no significant interference was observed for the My5-FU assay. Hemolytic samples should not be used as there is a risk that DPD was released from blood cells. This would lead to 5-FU degradation and falsely low results.
1. What is the most relevant PK parameter for docetaxel?
The PK parameter most relevant for docetaxel is the AUC (area under the curve). Saladax provides a simple to use Excel calculation program to calculate docetaxel AUC.
2. Why do I need to collect two samples for docetaxel AUC determination?
Docetaxel does not reach a steady state concentration during the infusion, therefore two samples need to be collected. The docetaxel concentrations at the two time points are used in a NONMEM regression program to calculate the AUC. Saladax provides a simple Excel program that can be used to determine docetaxel AUC.
3. Is there a sample stabilizer for MyDocetaxel?
No, there is no stabilizer for MyDocetaxel. Docetaxel blood samples should be placed on ice immediately after the blood draw to stabilize the analyte and should be centrifuged within 12 hours.
1. What is the relevant PK parameter for paclitaxel?
Time Above Threshold (Tc) is the most relevant pharmacokinetic parameter for paclitaxel. The time of 24 hours (range of 18 to 30 hours) above a paclitaxel plasma concentration of 0.05 μmol/L (Tc>0.05) has been shown to be the most relevant predictor of (haematological) toxicity, and also clinical outcome.
2. Is there a sample stabilizer for MyPaclitaxel?
No, there is no stabilizer for MyPaclitaxel. Paclitaxel samples should be placed on ice immediately after the blood draw to stabilize the analyte and should be centrifuged within 12 hours.
3. Do the taxane samples have to be centrifuged at 4°C or can they be centrifuged at room temperature?
Blood specimen can be centrifuged at room temperature.