Called for a retest

Question

My baby had the heel prick test and has been called for a retest. I am going out of my mind with worry.

Does this mean they have identified the defective gene? Does every suffered diagnosed always get called for the dreaded retest?

Answer

Hello questioner

Babies are screened at birth for CF using a heel prick test (Guthrie Test) which involves collection of a blood sample. If the results of the blood spot test reveal very high levels of a substance called Immunoreactive Trypsin (IRT) this can be characteristic of CF, but raised IRT can also be found in healthy infants. In healthy babies the IRT values return to normal within the first weeks of life however in babies with CF IRT values are raised for several months.
Occasionally you will be called for a retest after the first test and asked to give a second blood sample from your baby’s heel. This may be because there was not enough blood collected, or the result was borderline or unclear. In many centres if the initial heel prick test shows raised IRT then other tests are done to confirm the diagnosis. Early diagnosis of CF is essential to ensure your baby gets the proper support and early treatment required. I have added a refernce which summarises the methods of diagnosis in CF.

Best wishes
Stuart
Cystic fibrosis: terminology and diagnostic algorithms K De Boeck1, M Wilschanski2, C Castellani3, C Taylor4, H Cuppens5, J Dodge6, M Sinaasappel7 on behalf of the Diagnostic Working Group Thorax 2006;61:627-635

24.11.2008

Prof. Ballmann commented on the different approches of the screening (24.11.08):

In Europe there are indeed very different screening approaches as Helge
Hebestreit noticed.The general idea behind a second test before sending a
baby to a Cf-center and performing a sweat test, is to confirm the suspicion
that an elevated IRT might due to CF. The specificity of initial increased
IRT is not as high as one might expect. Therefore a second test is needed to
reduce the number of unnecessary sweat tests.In some countries a CFTR
mutation analysis (4 to 30 or even more mutations)is done from the same
Guthrie test card as it was used for IRT measurement. Only those persons
with one or two CF causing mutations were invited to a sweat test. In this
case the second test happens without worries for the family. On the other
hand the genetic testimng is more expensive than a second IRT test.

Kind regards

Manfred Ballmann