Guidance

4. Repeat blood spot samples

Updated 8 October 2024

Laboratories request repeat blood spot samples for a variety of reasons. A repeat sample must be taken as advised by the laboratory. There are 2 types of repeat samples. These are ‘avoidable repeat’ and ‘unavoidable repeat’ samples.

1. Avoidable repeat samples

Avoidable repeat samples are repeat samples that can be avoided. This could be due to:

• insufficient blood
• inappropriate application of blood
• incomplete or inaccurate data on the card
• a delay in the laboratory receiving the sample
• contamination of the sample
• a pre-transfusion/admission sample and day 5 sample on the same card
• damage to the sample in transit
• use of an expired card
• a sample taken when the baby was too young

Take an avoidable repeat sample within 72 hours of receipt of the request unless the baby is undergoing blood transfusions.

1.1 Harms caused by avoidable repeat samples

Avoidable repeat samples can cause anxiety for parents, distress to babies and delays in the screening process. This could lead to delayed identification and treatment of an affected baby. Avoidable repeats also waste healthcare resources (each repeat costs the NHS around £100). In some cases parents may refuse to consent to a repeat, this means that the baby will have incomplete screening.

1.2 Blood spot quality

A good quality blood spot sample is:

• taken at the right time
• has accurate and complete data
• contains enough blood to perform all tests
• 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.

Evidence shows that poor quality samples could 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).

Newborn screening laboratories in England follow a national, evidence based procedure on blood spot quality, with standardised consensus agreed acceptance and rejection criteria. To make sure that laboratories do not request an avoidable repeat, sample takers must obtain 4 good quality blood spots and complete all fields on the blood spot card accurately. The guidelines for newborn blood spot sampling provide more information.

1.3 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.

1.4 Inappropriate application of blood

Do not:

• apply several small spots of blood to the circle (multi spotted sample) because this can give a false negative result
• apply pressure to the spot to spread the blood out to fill the circle (compressed sample); compressed blood spots have a significantly higher risk of a false negative result
• layer one spot of blood directly on top of another or apply blood to the front and back of the blood spot card because this can give a false positive result

1.5 Incomplete or inaccurate data on the card

Incomplete or inaccurate data on the blood spot card, for example, no/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.

If you do not have the NHS number, you can obtain it from the:

• child health records department/child health information service
• GP practice

1.6 Delay in laboratory receiving the sample

It is important that the laboratory receives the blood spot card promptly so that they can refer screen positive babies quickly. Timeliness of despatch enables early analysis and subsequent treatment.

Post the blood spot sample in the prepaid/stamped addressed envelope (first class) on the same day (if not using a courier). If this is not possible, despatch within 24 hours of taking the sample. Do not delay despatch in order to batch blood spot cards together for postage.

If a post box is used, make sure it is one that is emptied daily (Monday to Saturday). Laboratories will reject samples received more than 14 days after the sample was taken due to the risk of an inaccurate result.

1.7 Contamination

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

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

This can cause confusion and lead to inaccurate results.

1.9 Damaged in transit

Samples damaged in transit can give inaccurate results.

1.10 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.

1.11 Taken when the baby was too young

This is when a sample is taken before day 5 (excluding pre transfusion samples). This may give rise to a false positive result for congenital hypothyroidism (CHT). It is important to calculate day 5 using day of birth as day 0. Sample takers should be aware that some IT systems record day of birth as day one, and this may result in taking the sample too early.

2. Unavoidable repeat samples

Unavoidable repeats are repeat samples that are required for clinical reasons, such as:

• prematurity
• borderline thyroid stimulating hormone (TSH) results
• inconclusive cystic fibrosis (CF) screening
• blood transfusions

2.1 Prematurity

Prematurity can mask CHT. Babies born at less than 32 completed weeks gestation (less than or equal to 31 weeks + 6 days) need a second blood spot sample taken, 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 hospital, whichever is sooner.

The healthcare professional (HCP) should follow the steps below to take the second sample.

1. Give parents a copy of Screening tests for you and your baby: babies in special care units.
2. Explain to parents that a repeat sample is recommended as the routine day 5 test may not pick up CHT in babies born at less than 32 completed weeks gestation.
3. Take the repeat sample at either 28 days of age or immediately before the baby is discharged home (whichever comes first).
4. Fill 2 circles on the card with blood and write ‘CHT preterm’ in the card’s comments box. If the baby is being discharge home before 28 days of age, write ‘discharged home’ on the card.

Prematurity can also mask sickle cell disease (SCD). The laboratory will request a repeat sample if needed.

2.2 Borderline TSH results

This is when the result is borderline for CHT. Another sample is required to confirm the result. The repeat sample must be taken 7 to 10 days after the initial borderline sample to detect any meaningful change in TSH levels.

Fill 4 circles on the card with blood and mark the card ‘CHT borderline’.

Make parents aware of the 2 possible outcomes from this repeat test.

1. CHT not suspected. The HCP should inform the baby’s parents directly and as soon as possible to relieve anxiety (this can be by telephone).
2. CHT suspected. The newborn screening laboratory refers the baby directly to a paediatrician. If the result is another ‘borderline’ then the baby will also be referred.

2.3 Inconclusive CF screening

This is when the result of the initial blood spot screening test for CF (immunoreactive trypsinogen (IRT)) is inconclusive and requires follow up.

A second blood spot sample should be collected on day 21 (and no later than day 24 in exceptional circumstances) (day of birth is day 0). If the baby is already older than this, the second blood spot sample should be collected as soon as possible or as advised by the laboratory. Mark the blood spot card ‘second IRT’. If the baby is older than 8 weeks (56 days), do not collect the repeat blood spot sample. In this situation inform the screening laboratory immediately so that appropriate arrangements can be made for the baby to be followed up.

Information sheets on the second IRT are available for HCPs and parents.

You must make parents aware of the 3 possible outcomes from this repeat test.

1. Not suspected. Most babies requiring a repeat test for CF will have this result. The HCP should inform the baby’s parents directly and as soon as possible to relieve anxiety (this can be by telephone).
2. Carrier of CF. The baby is a healthy carrier of the CF gene and will not need any further follow up. A HCP will contact the family to discuss the result.
3. CF suspected. There is a small possibility that the baby may be affected with CF In this case the baby will be referred by the newborn screening laboratory directly to a CF specialist.

2.4 Blood transfusions

When a baby has had a blood transfusion before the day 5 sample, another sample (4 blood spots) is needed at least 3 clear days after the last transfusion for CF, CHT and inherited metabolic disease (IMD) screening. This allows time for metabolite concentrations to return to pre transfusion levels.

You must record the date of the last blood transfusion on the blood spot card and on discharge or transfer notifications.

3. Explaining repeat samples to parents

It is important to inform 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.

The sample taker should explain:

• why a second blood spot is needed to complete screening
• when the parents can expect to receive the result
• whom to contact if they do not receive the result
• if their baby has a positive screening result they will be contacted as soon as the result is available

If the family no longer lives in the original area of birth this request should be passed on to the responsible HCP 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.

An information sheet is also available for parents and carers that explains:

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

4. Taking a repeat sample

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

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

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

5. Results

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 (every effort must be made to complete the test within 7 days).

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

6. Monitoring avoidable repeats

The screening programme monitors avoidable repeat rates by analysing key performance indicator data.

The acceptable avoidable repeat rate is less than or equal to 2% (that is, 1 in 50 samples), but HCPs should aim to achieve a rate of equal to or less than 1% (that is, 1 in 100 samples).