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Congenital Hypothyroidism (CHT)

The test used to screen for CHT is thyroid stimulating hormone (TSH), which is measured by immunoassay (AutoDELFIA®).

All raised TSH levels (>5 mU/L) are checked in duplicate on the original sample and the average result is taken.  Samples with confirmed levels >20 mU/L are treated as positive and urgent follow up is arranged at RMCH, unless the baby was still in a local hospital in which case follow up is initiated by the corresponding medical team.

Confirmed TSH levels between 8 and 20 mU/L are treated as borderline and a repeat sample is requested, to be taken 7-10 days after the first sample, to allow for normalisation of transient increases. If the borderline result is persistent or has moved into the positive range (>20 mU/L) clinical follow up is initiated at RMCH.

Babies born at a gestation of less than 32 weeks require a repeat sample on day 28 (date of birth counted as day 0) or at discharge from hospital, whichever is sooner.

Transient hypothyroidism can be related to prematurity, acute illness, drugs, maternal antibodies, maternal iodine supplements and exposure to iodine-containing compounds in imaging/surgery.

In the case of a positive CHT result on screening, the laboratory will telephone the relevant community midwives office and request that a midwife visits the family the same afternoon, unless it is a Friday. If a positive result occurs on a Friday, the midwife should visit on Sunday to inform the family. The appointment takes place the following working day (unless advised otherwise) and the family should report to the Medical Investigations Unit on Ward 76 of RMCH, as close to 9am as possible.

Once on the ward the following will be performed: blood tests for thyroid function on baby and mother, clinical examination and thyroid scan of baby. When the results of the tests are available (usually around lunchtime) a doctor will discuss them with the family. If hypothyroidism is confirmed treatment (in tablet form) will commence immediately. Advice will be given on the condition and how best to give the tablets. The visit is usually complete by mid-afternoon.

At the initial home visit the family should be given a copy of the ‘Congenital Hypothyroidism is suspected’ leaflet.

Phenylketonuria (PKU)

The test used to screen for PKU is phenylalanine (phe), which is measured by tandem mass spectrometry.

Tyrosine is used as a second line test. Initial clinical investigation, follow-up and treatment are carried out by the metabolic team at RMCH. In the case of a positive PKU result on screening, the specialist metabolic nurse will telephone the relevant community midwife with instructions on how to proceed and will organise an urgent appointment at RMCH for the following working day.

Elevated phe results can be also be caused by liver dysfunction, parenteral nutrition, galactosaemia, tyrosinaemia type 1 and disorders of pterin metabolism. Diagnostic testing includes analysis of blood amino acids and pterins.

Sickle cell disease (SCD)

Separation and identification of haemoglobin fractions to screen for SCD is carried out by high performance liquid chromatography (HPLC; ion exchange) using the BIORAD Variant NBS analyser. Any abnormal results are confirmed by second line testing using Isoelectric Focusing (IEF; performed by Specialist Haematology, MRI).

Local laboratory turnaround time standards (developed in 2012 following an audit):

  • L1: Receipt of sample in NBS Lab to referral of sample to haematology lab for isoelectric focusing – 3 working days.
  • L2: Receipt of sample in haematology lab to entry of IEF result into screening information system – 5 working days.
  • L3: Entry of IEF result into screening information system to printing of referral letters – 1 working day.

The Manchester Sickle Cell and Thalassaemia Centre (MSCTC) inform parents of positive screening results within 5 days of receiving the results or sooner if the baby is approaching 4 weeks of age. Clinical follow up of SCD positive patients is carried out by the Consultant Paediatric Haematologists at CMFT. Parents are informed of carrier results in person, by the Screening Link Health Visitor for their area.

For transfused babies, where no pre-transfusion sample is available, screening is completed by referring the sample for mutation analysis for Haemoglobin S.

For any high risk couples (1 in 4 risk of a significant haemoglobinopathy), a Manchester ‘at risk’ pregnancy alert form should be completed by maternity and sent to the screening lab and the Manchester Sickle Cell Centre.

Download the Manchester ‘at risk’ pregnancy alert form

Medium-chain acyl-CoA Dehydrogenase Deficiency (MCADD)

The test used to screen for MCADD is octanoylcarnitine (C8), which is measured by tandem mass spectrometry.

Initial clinical investigation, follow-up and treatment are carried out by the metabolic team at RMCH.

In the case of a positive MCADD result on screening, the specialist metabolic nurse will telephone the relevant community midwife to check that the baby is fit and well and taking oral feeds normally. An urgent appointment is made at RMCH for the following day (e.g. babies referred on Fridays are seen on Saturday). If there are any concerns, the baby should be admitted to the local hospital immediately.

Diagnostic testing includes urine organic acid analysis and mutation analysis.

Cystic Fibrosis (CF)

The test used to screen for cystic fibrosis is Immunoreactive trypsinogen (IRT), which is measured by immunoassay (AutoDELFIA®).

Elevated results (above the 99.5th centile) undergo mutation analysis (panel of 4 common mutations). If no mutations are identified yet the initial IRT is above the 99.9th centile, a second sample is collected on day 21, for repeat IRT analysis. If one mutation is identified, a larger panel of mutations is tested. Babies with one mutation detected require a second sample on day 21, for repeat IRT analysis.

Any baby with two mutations or two raised IRT results is referred as ‘CF suspected’. Clinical follow up of positive CF cases is usually undertaken by the regional CF team at RMCH, however, there are a few hospitals within the region that carry out their own clinical follow up in collaboration with the regional CF centre (shared care centres). Sweat testing is the diagnostic test for cystic fibrosis. Further genetic testing may also be undertaken. Sweat testing for screen positive cases takes place on Thursdays at RMCH. Families have an appointment with the CF team the same day as the sweat test.

False negative screening results have been reported in some premature babies and may also be associated with viral infection leading to acute gastroenteritis or respiratory illness. Babies with CF and meconium ileus may have a low IRT in the first week. False positive results have been reported in conjunction with chromosomal abnormalities, renal failure, bowel atresia, congenital infections and extreme prematurity. Elevated IRT concentrations can also occur in children who are sick on PICU.

Cut-offs for IRT testing vary with kit lot. The 99.5th centile is determined from local data and we also take part in a national collaboration at each kit lot change (pilot use of new kit lot and data combined from all labs using kit lot). Together these processes help ensure that appropriate cut-offs are in use.

Isovaleric acidaemia (IVA)

The test used to screen for IVA is isovalerylcarnitine (C5), which is measured by tandem mass spectrometry.

Initial clinical investigation, follow-up and treatment are carried out by the metabolic team at RMCH.

In the case of a positive IVA result on screening, the family is contacted by the metabolic team and the baby attends RMCH the same day for clinical assessment and diagnostic testing. If the baby is acutely unwell then an urgent admission will be required.

Diagnostic testing includes urine organic acid analysis and mutation analysis. Some antibiotics can cause false positive results in the IVA screen.

Maple syrup urine disease (MSUD)

The test used to screen for MSUD is leucine/isoleucine/alloisoleucine, which is measured by tandem mass spectrometry.

Initial clinical investigation, follow-up and treatment are carried out by the metabolic team at RMCH.

In the case of a positive MSUD result on screening, the family is contacted by the metabolic team and the baby attends RMCH the same day for clinical assessment and diagnostic testing. If the baby is acutely unwell then an urgent admission will be required.

Diagnostic testing includes analysis of urine organic acids and blood amino acids.

Glutaric aciduria type 1 (GA1)

The test used to screen for GA1 is glutarylcarnitine (C5-DC), which is measured by tandem mass spectrometry.

Initial clinical investigation, follow-up and treatment are carried out by the metabolic team at RMCH.

In the case of a positive GA1 result on screening, the family is contacted by the metabolic team and the baby attends RMCH the same day for clinical assessment and diagnostic testing. If the baby is acutely unwell then an urgent admission will be required.

Diagnostic testing includes urine organic acid analysis and mutation analysis.

Homocystinuria (pyridoxine unresponsive; HCU)

The test used to screen for HCU is methionine, which is measured by tandem mass spectrometry. Total homocysteine is used as a second line test.

Initial clinical investigation, follow-up and treatment are carried out by the metabolic team at RMCH.

In the case of a positive HCU result on screening, the specialist metabolic nurse will telephone the relevant community midwife with instructions on how to proceed and will organise an appointment at RMCH for the following working day.

Diagnostic testing includes blood amino acid analysis. Liver disease and parenteral nutrition may cause elevated methionine results. Early metabolic screening is not required for this condition.

 

Condition Analyte Method 2nd line test
Congenital Hypothyroidism (CHT) Thyroid stimulating hormone (TSH) Immunoassay (AutoDELFIA®) Not applicable
Phenylketonuria (PKU) Phenylalanine (Phe) Tandem Mass Spectrometry (MS/MS) Tyrosine
Sickle Cell Disease (SCD) Separation and identification of haemoglobin fractions HPLC (ion exchange) using BIORAD Variant NBS Isoelectric Focusing (IEF)
Medium-chain acyl-CoA Dehydrogenase Deficiency (MCADD) Octanoylcarnitine (C8) Tandem Mass Spectrometry (MS/MS) Not applicable
Cystic Fibrosis (CF) Immunoreactive trypsinogen (IRT) Immunoassay (AutoDELFIA®) Mutation analysis
Isovaleric acidaemia (IVA) Isovalerylcarnitine (C5) Tandem Mass Spectrometry (MS/MS) Not applicable
Maple syrup urine disease (MSUD) Leucine/isoleucine/alloisoleucine Tandem Mass Spectrometry (MS/MS) Not applicable
Glutaric aciduria type 1 (GA1) Glutarylcarnitine (C5-DC) Tandem Mass Spectrometry (MS/MS) Not applicable
Homocystinuria (pyridoxine unresponsive; HCU) Methionine Tandem Mass Spectrometry (MS/MS) Total homocysteine