ICID > Clinical Management > Maternity Neonatal > Newborn screening for Phenylketonuria and Hypothyroidism  

Newborn screening for Phenylketonuria and Hypothyroidism 

  • 1. Indications
  • 2. Clinical Management
  • 3. Patient Information
  • 4. Audit
  • 5. Evidence Base
  • 6. Appendices
  • 1. Indications

    All babies born in the United Kingdom are tested shortly after birth for two conditions (Phenylketonuria and Congenital Hypothyroidism) which, without timely diagnosis and treatment, lead to irreversible mental retardation.  Both tests are carried out in centralised laboratories on blood collected by heel-prick, and the screening programme should ensure that ALL infants are tested, and that any infant with PKU or Congenital hypothyroidism starts treatment within the FIRST THREE WEEKS of life.


    AIM  To screen 100% of the newborn population for PKU and congenital hypothyroidism and detect 100% of all positive cases so that appropriate treatment commences by 21 days of age.

    2. Clinical Management





    1   Identification of neonates to be screened.  This is by:-

    ·         Birth notification.

    ·         Concealed deliveries to be notified as soon as apparent.



    ·         Parents to be given a verbal and written explanation of the nature and purpose of the screening programme, by the midwife, prior to testing on the 6th day.  The midwife should ensure the parent understands the procedure, through discussion and use of the information leaflet.


    ·         Heel prick blood sample to be taken onto nationally approved filter paper card (Schleicher & Schuell 903). Salisbury cards are colour coded black in the top right hand corner.

    ·         The sample should be taken on or after the 6th day from all babies irrespective of the method of feeding, current illness or treatment.  NB  The detection of PKU depends on an adequate intake of protein, defined as at least 72 hours of oral milk feeds before the blood sample is taken.  The first sample may therefore be UNSUITABLE for PKU testing (e.g. in neonates on intravenous feeding regimes), and a repeat sample will be necessary.  The feeding regime should be CLEARLY written on the filter paper card in such cases so that the Laboratory is aware.  A repeat sample will be requested by the Laboratory but it is the responsibility of the staff on NICU to obtain the repeat sample after 72 hours of full milk feeds.  The Laboratory will monitor that a suitable repeat sample is received.


    ·         Ensure the foot is warm.

    ·         Clean the site with a Mediswab (optional)and ensure it is dry.

    ·         Vaseline may be used to help a droplet of blood to form.

    ·         Squeeze the skin taut and perform the puncture firmly with a Microtainer Lancet in one of the fleshy sides of the heel.

    ·         Wait for a drop of blood to form before touching the drop to the first circle on the collection card.  Ensure the blood fills the circle and soaks right through to the back of the card.

    ·         Allow further drops of blood to form and fill all four circles with blood.  NOTE: Small poorly collected spots may mean that the sample has to be repeated.

    ·         DO NOT contaminate the filter paper with water, alcohol or any other fluid.  The card may be stored in a fridge ONLY if the blood has thoroughly dried on the paper.

    ·         N.B.  If a midwife is asked to collect a repeat sample she should ensure that she knows the reason why the repeat test is required, and explain the reason to the parent(s).


    5   RECORDS

    ·         Complete all the details on the card.

    ·         In the comments section record if the baby is Nil by Mouth, receiving IV feeding, sibling has PKU, receiving antibiotics or it is a repeat sample.  This information enables the correct interpretation of results.

    ·         Record that the sample has been taken and sent in the baby's care plan.  Retain the top copy of the request form and attach it to the baby's care plan.

    ·         Place the card in its protective envelope and keep it away from heat.

    ·         If a parent refuses to allow a sample to be taken send the completed card to the Laboratory without any blood on it.  Senior Laboratory staff will contact the parents with further information.  The top copy should be retained in the baby's care plan as above.  The parents should be asked to sign a "refusal of screening test" form.  This form should be filed in the baby's hospital notes.



    ·         All samples are sent to:-  Newborn Screening Laboratory, Department of Laboratory Medicine, Pathology, Salisbury Health Care NHS Trust, Odstock, Salisbury, SP2 8BR (Tel ext 4051)


    ·         Ideally samples should be delivered to the Laboratory on the day of collection.

    ·         Samples may be taken to Beatrice reception.  The receptionist delivers them to the laboratory daily except at weekends.

    ·         The sample may be delivered directly to the Pathology reception.

    ·         Samples taken at a weekend may be stored in a ward fridge and delivered to the Laboratory first thing on Monday morning.




    When samples are recieved, the blood spots are visually checked for


    Repeat samples will immediately be asked for in the following circumstances:-

    ·         Sample taken before the 6th day of life (Unsuitable for PKU)

    ·         Sample taken before the infant has had 3 days of oral milk feeds. (Unsuitable for PKU)

    ·         Sample received by the laboratory more than 13 days after it was taken.
    (Unsuitable for PKU/TSH)

    ·         Sample insufficient for analysis (very small spots and/or not soaked through to back of card) (Unsuitable for PKU/TSH)

    ·         Sample obviously contaminated with fluid, e.g. water, urine, formalin etc.
    (Unsuitable for PKU/TSH)


    These unsuitable samples will normally be processed by the laboratory in the usual way, but will be reported as UNSUITABLE FOR TSH AND/OR PKU.  Exceptionally, a sample will not be analysed at all (e.g. if the card is soaking wet when it arrives).

    Any observed shortcomings in the sample collection procedure will be relayed to the appropriate person in the District, so that problems can be identified and rectified rapidly.

    The laboratory constantly monitors the age at testing, and the time taken for samples to reach it.  An appropriate person in the District will be contacted if a problem is identified.  The Post office will be contacted if appropriate.



    ·         Repeat samples may be required for a variety of reasons, including insufficient blood, unsuitable sample, technical problems or an equivocal result for one or both tests.

    ·         When a repeat sample is required, either upon receipt of the sample or after testing is complete, the appropriate midwifery co-ordinator is contacted by telephone.

    ·         Each request for a repeat sample includes a clear explanation of the reason for the repeat test to avoid unnecessary parental anxiety.



    ·         Requests for repeat samples are recorded and monitored to ensure that repeat samples are received within an acceptable time.

    ·         If a repeat test is to be carried out by another screening laboratory, details of the request for a repeat sample are relayed to that screening laboratory whenever possible.

    ·         Any shortcomings indentified by the monitoring are relayed to an appropriate person.


    ·         Batches of samples are processed each weekday (excepting Bank Holidays).
    Each batch of samples is stored at room temperature, out of direct sunlight/heat.

    ·         Methodology and procedures are documented and both external and internal quality control systems are applied.

    ·         All results are available within 4 working days

    5              REPORTING AND Interpretation of results

    ·         A database is maintained of all samples received, and results are entered onto the database as soon as they are available.

    ·         Results are interpreted and reported by experienced senior staff with a second check by another member of staff.

    ·         Results are reported as:-                  



    requiring no further action


    requiring follow up


    requiring immediate urgent action


    requiring a repeat sample


    Action taken (Positive results):-

    ·        A positive result is confirmed by reanalysis the following day, using a fresh blood spot from the card.

    ·        Once confirmed, the result is urgently telephoned to the Consultant Paediatrician on call by a senior member of staff.  Neonates with presumptive PKU or CH are referred to Dr Carl Taylor.

    ·        An internal record sheet is filled in.  This has details of the child, sample, G.P. and Paediatrician.

    ·        The result is confirmed in writing within 24 hours, using a standard letter, with copies to the GP, the Health Visitor, the designated Community Paediatrician (Dr Lwin), and for Congenital Hypothyroidism, the Regional Co-ordinator Dr. Peter Betts at Southampton General Hospital.  Follow-up information is requested.

    ·        The confirmatory test result and date the infant was seen by Dr Carl Taylor are sought and added to the internal record sheet.


    Action taken (Equivocal Results):-

    ·        An equivocal result is confirmed by reanalysis the following day, using a fresh blood spot from the card.

    ·        Once confirmed, a senior member of staff will decide on the appropriate follow-up action required, record this action on the back of the card, and liaise with the Clerical Officer.

    ·        If the equivocal result is on a first sample, the Clerical Officer will telephone the appropriate person within the district, and request a repeat blood spot sample, explaining the reason for the request, and advising when to obtain the sample (e.g. after 3 days of full oral milk feeds).

    ·        If the equivocal result is on a repeat sample, a senior member of staff will decide what appropriate action should be taken.  Normally, a standard letter is sent to the child's G.P., recommending referral to Dr Carl Taylor and explaining the nature of the abnormalities noted.  A third blood spot sample may sometimes be requested.

    Action taken (Negative Results):-

    ·      Negative results are reported to the District Health Authority through the Child Health Computing Department.



    ·               Results are printed three times a week (usually Monday, Wednesday, Friday), onto sticky labels. All abnormal results are highlighted.

    ·               Results are also sent, via E-Mail, to the Lotus Notes database in CHC.  Results are available within 6 hours of printing.

    ·               2 sets of printed sticky labels are sent by internal post to a designated person within the Child Health Computing department.


    PKU Results are reported as follows:-



    Phenylalanine slightly raised


    Tyrosine slightly raised


    Phenylalanine/Tyrosine high


    Unusual amino acid pattern




    Unsuitable - TPN


    Unsuitable - Contaminated


    Unsuitable - Delayed Receipt


    Unsuitable - Insufficient


    Insufficient - Technical Problem

    TSH Results are reported as follows:-



    TSH slightly raised




    Unsuitable - Contaminated


    Unsuitable - Delayed Receipt


    Unsuitable - Insufficient


    Insufficient - Technical Problem





    ·         Results are available on computer from 1983 onwards.


    ·         Telephone and written enquiries from the Child Health Department are dealt with promptly.  Written enquiries are dealt with within 24 hours of receipt. If there is no record of a child, the Clerical Officer telephones Child Health Computing.  If there is a record, a written reply is sent by internal mail within 24 hours.


    ·         Telephone and written enquiries from Clinicians, Midwives, Health Visitors, Adoption Agencies, and other screening laboratories are dealt with promptly.


    8        SAMPLE STORAGE


    ·         Blood spot sample cards are stored at room temperature for 22 years.

    ·         A card may be released for DNA analysis, on written application, accompanied by a consent form (available from the Laboratory) signed by the infant's parent/legal guardian.




    • On receipt of notification of PKU/TSH results from the Newborn Screening Laboratory (NSL) the results will be entered on the District Child Health Computer within 3 working days
    • The respective Health Visitor will be notified of the result, via the sticky label generated by the NSL, within 4 working days
    • For children for whom there is no result within 21 days, the Child Health Computer will generate a list.  This list will be sent to the Screening Laboratory after each batch entry to facilitate a check against their register
    • In the event that no result has been received by the Community Child Health Department by 28 days, CCHD will notify the respective Health Visitor that a result is outstanding.
    • For children aged 0-6 months, who have moved into the District and for whom there is no evidence of a PKU/TSH test being done, CCHD will notify the respective Health Visitor and request the results from the previous District Health Authority


    ·         In the event of parent refusal, Health Visitor to be informed.

    ·         It is the responsibility of the Health Visitor to ensure that a result has been received and recorded, by 28 days of age, on all babies on case load.

    ·         In the event of a result not having been received by 28 days, it is the responsibility of the Health Visitor to establish whether the neonate was screened and the reason for any non-screening.  (Contact Child Health Computing Ext 2075 or NNS Laboratory Ext 4051)

    ·         At 28 days, if no PKU/TSH test has been done, it is the responsibility of the Health Visitor to ensure that the test is carried out and the result is recorded in the child's notes (unless testing refused).


    ·         A senior member of staff from the Screening Laboratory will contact the Consultant Paediatrician on call when a positive screening test for PKU or CH has been confirmed.  For neonates with PKU, responsibility will be given to Dr Carl Taylor for joint management with the Dietetics Department.  In neonates with CH, responsibility will be given to Dr Carl Taylor.

    ·         The mother's GP and the parent(s) will be contacted by telephone as soon as possible by the consultant paediatrician.

    ·         The neonate and parent(s) will be seen on the next working day.

    ·         For neonates with PKU confirmation of diagnosis will be by an urgent venous blood amino acid profile (0.5 ml clotted blood) plus 0.5 ml clotted blood for Biopterin metabolites to exclude Biopterin pathway defects.

    ·         For neonates with CH confirmation of diagnosis will be by a rapid venous blood TSH and Free T4 (with Free T3 if possible).  1-1.5 ml clotted blood is required for a full thyroid profile.

    3. Patient Information

    4. Audit

    5. Evidence Base

    6. Appendices

    Document Owner Brian Moody 
    Review Date
    Document Status
    Revision Number