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Correct identification of screening samples

Newborn blood spot screening used to be referred to as the Guthrie test or sometimes just the ‘PKU’ test. Some health professionals continue to use the historical terminology, which can be confusing.

Blood spot samples collected from patients with phenylketonuria, for monitoring purposes, are analysed by the Willink laboratory and must be addressed to the Willink laboratory not the Newborn Screening laboratory.

If newborn screening samples are labelled as ‘PKU’, this can lead to the incorrect analysis being performed and/or delays to screening. Please use the correct terminology when making enquiries and sending samples, to avoid confusion.

Sample collection

Samples for newborn screening should be collected on day 5 (where date of birth is day 0), unless there are exceptional circumstances.

Care should be taken to ensure that the filter paper card has not exceeded the expiry date printed. At least 4 blood spots, the size of the guide circles on the card, should be collected. See the guidelines for newborn blood spot sampling

Samples with the following problems will be rejected and a repeat sample requested: collected <5 days, collected less than 3 clear days after the last transfusion, insufficient sample (too small/not soaked through), incorrect blood application (multi-spotted/spotted both sides), compressed/damaged, possible faecal contamination (CF), missing/invalid NHS number, missing/invalid date of sample/date of birth, expired card, >14 days in transit or damaged in transit.

A repeat sample from the avoidable repeat category must be taken within three calendar days of receipt of request.

When completing the blood spot card, please write the Trust code for your maternity unit/neonatal unit in the sample taker’s trust field on the blood spot card to improve the accuracy of the figures.

A list of Trust codes is provided in the table below. Alternatively maternity units could stamp cards with the code prior to issuing to midwives/neonatal units, depending on local arrangements. It would also be helpful if health visitors could write ‘HV’ in the sample taker’s trust field, so that we can provide data specific to health visitors.

Code Trust name
RXL Blackpool Teaching Hospitals NHS Foundation Trust
RMC Bolton NHS Foundation Trust
RW3 (R0A) Manchester University NHS Foundation Trust – ORC
NM-R0A Manchester University NHS Foundation Trust – North Manchester
RXR East Lancashire Hospitals NHS Trust
RXN Lancashire Teaching Hospitals NHS Foundation Trust
OL-RW6 Northern Care Alliance (Oldham)
RVY Southport and Ormskirk Hospitals NHS Trust
RWJ Stockport NHS Foundation Trust
RMP Tameside Hospital NHS Foundation Trust
RM2 (R0A) Manchester University NHS Foundation Trust – Wythenshawe
RTX University Hospitals of Morecambe Bay NHS Foundation Trust
RRF Wrightington, Wigan and Leigh NHS Foundation Trust

Tips to help avoid rejection of samples:

  • Collect sample on day 5 (date of birth is day 0)
  • Check the expiry date on the card
  • Wash the baby’s heel with water to reduce the risk of a contaminated IRT result
  • Ensure that blood spots are the size of the guide circles on the card
  • Allow the blood to drop onto the card rather than touching the filter paper to the baby’s heel
  • Some brands of lancet device are more effective than others
  • Extra blood spots, in addition to the 4 indicated by the guide circles, can be collected elsewhere on the card
  • Repeat the test at the same visit if the spots are too small or have not soaked through to the back of the card
  • Make sure there is a valid NHS number on the card

Sample transport

Depending on the maternity unit, samples are sent via first class royal mail, courier or lab transport.

Where samples are sent from a central point, some areas have arranged to include a ‘sample audit’ form in each envelope.

When samples are received in the lab, the form is faxed back to the maternity unit to confirm receipt.

Please contact us as soon as possible if you have any concerns about samples potentially lost in transit.

Dispatch ideally the same day but if this is not possible, then dispatch within 24 hours of taking the sample.

Dispatch should not be delayed in order to batch blood spot cards together for postage.


(Last reviewed June 2023)