Blood Spots for Phe Monitoring
Providing dried bood spots is necessary to measure phenylalanine (phe) levels.The ongoing monitoring of these levels is essential; it enables the dietitian to make dietary recommendations to ensure that the levels are maintained within normal ranges. The dietitian will advise on the frequency of blood spot testing required. It is important to provide good quality blood spots. If poor quality blood spots are received by the laboratory, they may not accept them as the results may be inaccurate.
It is important that you, and eventually your child, become used to providing good quality blood spots. If poor quality blood spots are received at the lab, they may not be accepted.
Blood spot samples are drops of blood, about a centimetre in width, that are placed onto a special testing card.
Your hospital team will have already shown you how to take a blood spot sample and will have provided you with all the supplies you need.
Always contact your dietitian or metabolic nurse at the hospital if you have any questions about blood spots or if you need any more blood spot sample supplies.
When your child is still a baby, you will use their heel to collect a blood sample.
As they grow up, you will use their finger or their thumb instead. To encourage blood flow, you should always make sure heels, fingers or thumbs are warm.
Before taking the blood spot sample, check the date on the testing card to make sure it has not expired and that all sections are completed.
These cards may already have a label on them with all your child’s details (it’s still always useful to double check these are correct). If not, you will need to add them to the card.
A step-by-step guide to providing a good quality blood spot sample:
1. Wash your hands and your baby’s heel if they are very young. As your child gets older and you start to use their fingers/thumbs to collect blood spots, you will need to make sure they wash their hands too.
2. Prick their heel, or finger or /thumb.
3. Allow a drop of blood to form.
4. Place the blood spot card up to the drop and allow it to drip onto the a circle on the card, as close to the centre as possible. Do not press the heel, finger or thumb against the card.
5. Repeat step 4 to provide blood into the onto the other 3 (three?) circles on the blood spot card.
6. Once you have finished, cover the prick site with a little cotton wool and apply light pressure; this should stop any bleeding almost immediately.
7. Allow the blood spot to absorb into the card and air dry enough so they lose the initial 'wet look' before putting the card into the envelope provided (if they are not air dry then they can stick to the inside and damage the card).
8. Send the blood spot sample card back to the hospital as soon as possible once you have completed it. This helps to make sure any changes to your child’s diet can be identified quickly by your dietitian.
Important points to remember:
• Have all the equipment ready before you start.
• Always take the blood spot sample at the time of day your dietitian has advised but it is usually best to measure early in the morning before the first feed of the day.
• Blood spots need to be taken from just 1 drop of blood, measuring 0.7mm – this is just under a centimetre in diameter.
Blood spots should be made from one single drop of blood and the diameter of the spot should be at least 0.7cm.
The dotted circles on the card measure 1cm.
If blood spots don’t meet this measurement and are taken from more than one drop of blood (overlapping on the card) the phe level result will not be accurate and will need to be repeated.
• Blood needs to be soaked right through the card so the lab can test it properly.
• If you have any questions at all about this process, contact your dietitian or the metabolic nurse at your
hospital.
