Guidance

Explaining repeat blood spot screening samples to parents: information for health professionals

Updated 20 September 2018

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Newborn screening laboratories ask for repeat blood spot samples for a variety of reasons. There are 2 types of repeat samples:

  • avoidable repeat
  • unavoidable repeat

Avoidable repeats are repeat samples that are needed because there is something wrong with the card, the blood sample or the timing of the sample.

Unavoidable repeats are repeat samples that are needed to complete screening for clinical reasons.

A repeat sample must be taken as advised by the laboratory. For avoidable repeat samples, this should be as soon as possible and within 72 hours of receipt of the request.

In some cases, parents may not agree to a repeat sample. This means that their baby will have incomplete screening.

1. Reasons for avoidable repeats:

1.1 Insufficient blood

If the circles contain a small blood spot or blood has not soaked through to the back of the card, there will be insufficient blood to complete screening accurately. This can give a false negative result.

1.2 Inappropriate application of blood

Applying several small spots of blood to the circle (multi-spotted sample) can give a false negative result.

Applying pressure to the spot to spread the blood out to fill the circle (compressed sample) leads to a significantly higher risk of a false negative result.

Layering one spot of blood directly on top of another or applying blood to the front and back of the blood spot card can give a false positive result.

1.3 Contamination

Contamination of the sample, for example if the card gets wet, will give an inaccurate result.

1.4 Taken when the baby was too young

This is when a sample is taken before day 5 (excluding pre-transfusion samples). It is important to calculate day 5 using day of birth as day 0. This can lead to a false positive result for congenital hypothyroidism.

1.5 Incomplete or inaccurate labelling on the card

Incomplete or inaccurate data on the blood spot card, for example no or inaccurate NHS number, date of sample or date of birth, will result in a repeat request because the baby cannot be accurately identified. This will delay treatment if the baby’s screening result is positive.

1.6 Expired card

The expiry date is for quality control. After this date, the quality of the filter paper and therefore the results cannot be guaranteed.

1.7 Pre transfusion/admission and day 5 sample on the same card

This can cause confusion and lead to inaccurate results.

1.8 Delay in laboratory receiving the sample

It is important that the laboratory receives the blood spot card promptly so that it can refer screen positive babies quickly. Laboratories will reject samples received more than 14 days after the sample was taken due to the risk of an inaccurate result.

1.9 Damaged in transit

Samples damaged in transit can give inaccurate results.

2. Reasons for unavoidable repeats

2.1 Prematurity

Prematurity can mask congenital hypothyroidism (CHT). Babies born at less than 32 weeks gestation (less than or equal to 31 weeks + 6 days) need a second blood spot sample in addition to the day 5 sample, to screen for this condition.

The second sample is taken when the baby reaches 28 days of age (day of birth is day 0) or on the day of discharge home from the hospital, whichever is sooner.

Inform parents that a repeat sample is recommended because the routine day 5 test may not pick up CHT in babies born at less than 32 weeks gestation.

Write in the blood spot card comment box ‘CHT preterm’.

Prematurity can also mask sickle cell disease (SCD). Some premature babies who show no haemoglobin A need a second sample to test for SCD.

Inform parents that a repeat sample is recommended because the routine day 5 test may not pick up SCD in premature babies.

Write in the blood spot card comment box ‘SCD preterm’.

2.2 Borderline congenital hypothyroidism result

This is when the result of the initial blood spot screening test for CHT is borderline. Another sample is required to establish a final screening result.

The repeat sample should be taken 7 to 10 days after the initial sample.

Inform parents of the 2 possible outcomes from this repeat test.

  • CHT not suspected. Most babies requiring a repeat test for CHT will have this result.

  • CHT suspected. About 15% of babies requiring a repeat test for CHT will have this result. In this case, the newborn screening laboratory will refer the baby directly to a pediatrician. If the result is another borderline, the laboratory will also be referred.

Write in the blood spot card comment box ‘CHT borderline’.

2.3 Inconclusive cystic fibrosis result

This is when the result of the initial blood spot screening test for cystic fibrosis (CF) is inconclusive. Another sample is required to establish a final screening result.

The repeat sample should be taken on day 21 (no later than day 24). If the baby is already older than this, the sample should be collected as soon as possible. If the baby is older than 8 weeks (56 days), the result of the repeat test would be unreliable. Do not collect the repeat sample and explain this to the parents. Inform the screening laboratory immediately.

Inform parents of the 3 possible outcomes from this repeat test.

  • CF not suspected. Most babies requiring a repeat test for CF will have this result.

  • Carrier of CF. About 35% of babies requiring a repeat test for CF will have this result. This means that the baby is a healthy CF carrier. A health care professional will contact the parents to discuss the result.

  • CF suspected. About 20% of babies requiring a repeat test for CF will have this result. In this case, the newborn screening laboratory will refer the baby directly to a CF specialist.

Information sheets on the second immunoreactive trypsinogen (IRT) test are available for healthcare professionals and parents.

Write in the blood spot card comment box ‘CF inconclusive’.

2.4 Blood transfusions

When a baby has had a blood transfusion before the day 5 sample, another sample is needed at least 3 clear days after the last transfusion. This allows time for metabolite concentrations to return to pre-transfusion levels.

The date of the last blood transfusion must be recorded on the blood spot card.

Write in the blood spot card comment box ‘post-transfusion’.

3. Explaining repeat samples to parents

It is important to tell parents why their baby needs a repeat sample. Research has shown that parents feel more satisfied with the screening process if the reasons for a repeat sample are clearly explained.

Tell parents:

  • why a second blood spot is needed to complete screening
  • that the result of most repeat samples is not suspected
  • when they can expect to receive the result
  • who they should contact if they do not receive the result
  • if one of the 9 conditions is suspected they will be contacted sooner

An information sheet for parents explains:

  • why a baby may need a repeat screening
  • how the test will happen
  • when to expect the results

4. Taking the repeat sample

When taking a repeat sample, the newborn blood spot screening sampling guidelines should be followed.

When completing the blood spot card, make sure that the:

  • ‘repeat sample’ box is ticked
  • reason for the repeat is written in the comments box

A good quality blood spot sample:

  • is taken at the right time
  • has accurate and complete labelling
  • contains 4 good quality blood spots
  • is sent to the newborn screening laboratory in a timely manner
  • is not contaminated

In the laboratory, several small discs are ‘punched’ (removed) from the blood spots to be used in the screening process. The sample needs to be sufficient to screen for all of the conditions and for further testing if required, for example to check a screen positive result.

Poor quality samples can lead to a baby with a condition being missed (false negative result) or referral of a baby without a condition for further tests (false positive result).

If the family no longer lives in the original area of birth this request should be passed on to the responsible healthcare provider according to local procedures. Copies of any ‘request for repeat sample’ documentation from the laboratory should be included. It is also essential to inform the screening laboratory that it has not been possible to take the sample and provide contact information. This must be done immediately.

5. Results

Most results from repeat blood spot samples are not suspected for all 9 conditions.

Parents may be anxious if their baby has had a repeat sample. They can expect to receive the results as soon as they are available. This is usually within 14 days of taking the sample.

It is important that families are reassured about normal results for the other screening tests as soon as possible.

6. Further resources

Resources to support healthcare professionals include:

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