Here is what I found in a quick search. I'll just copy and paste a few paragraph:
Testing first day. Hazardous for newborn. Hospital full of nasty germs.
First day? 2-7 days? The first day it will not have yet the high level of phenylalanine.
Ketone smell. Jaundice. Test not conclusive. Clinical disorders still possible.
Nothing a doctor could not see, looking at a baby.
But a lot of fearmongering for an occurence of one in 15000.
"We will discard the sample after testing, unless we keep it for further research, "
What types of blood tests do newborns need?
Although newborns can potentially require any type of testing, there are a handful of routine tests that are common in neonatal medicine:
Phenylketonuria (PKU) – This free, state-performed screening test is done as a public service for all newborns. Although its named after just one particular metabolic disorder, the test actually screens for about a dozen critical disorders, including thyroid dysfunction, sickle-cell anemia, and cystic fibrosis.
Bilirubin – Immediately after birth, many newborns can develop
jaundice, a yellowing of the skin and eyes caused by the buildup of bilirubin. Although a temporary condition, bilirubin levels need to be monitored with blood tests until the condition resolves.
Complete blood count – Usually called a CBC, blood counts are an important monitoring tool for a number of issues that can arise with neonates. CBCs are used to screen for anemia, infection, or disorders of red cell shape and function. These are usually performed on newborns that are staying in the hospital.
Genetic studies – A number of chromosomal disorders can be detected using the DNA contained within white blood cells.
Neonatal phlebotomy can be understandably intimidating. There are certain things to consider when performing a phlebotomy procedure on a young infant. Be cognizant of the fact that
their small body and thin veins are more vulnerable to damage, and use the utmost caution at all times. Also,
infants have a miniscule blood volume compared to adults, so only draw the amount needed for testing.
Their tininess does also have some benefits; unlike older people, babies cannot anticipate or remember pain, so there is no anxiety on their part. Parents, on the other hand, can create a bigger challenge. Always take the time to explain the procedure well, and offer compassion and reassurance for nervous parents. If you require their assistance in holding or restraining an infant, be certain of their competence to do so.
Distressed babies are notorious for erasing their parents’ ability to remain objective! If you do not feel the phlebotomy can be comfortably assisted by a parent, ask a coworker to help instead.
wiki
Signs and symptoms
Untreated PKU can lead to
intellectual disability,
seizures, behavioral problems, and
mental disorders.
[1] It may also result in a musty smell and lighter skin.
[1] A baby born to a mother who has poorly treated PKU may have heart problems, a
small head, and
low birth weight.
[1]
Because the mother's body is able to break down phenylalanine during pregnancy, infants with PKU are normal at birth. The disease is not detectable by physical examination at that time, because no damage has yet been done. Newborn screening is performed to detect the disease and initiate treatment before any damage is done. The blood sample is usually taken by a
heel prick,
typically performed 2–7 days after birth. This test can reveal elevated phenylalanine levels after one or two days of normal infant feeding.
[10][11]
If a child is not diagnosed during the routine newborn screening test and a phenylalanine restricted diet is not introduced, then phenylalanine levels in the blood will increase over time. Toxic levels of phenylalanine (and insufficient levels of tyrosine) can interfere with infant development in ways which have permanent effects. The disease may present clinically with
seizures,
hypopigmentation (excessively fair hair and skin), and a "musty odor" to the baby's sweat and urine (due to
phenylacetate, a carboxylic acid produced by the oxidation of phenylketone).
In most cases, a repeat test should be done at approximately two weeks of age to
verify the initial test and uncover any phenylketonuria that was initially missed.[
citation needed]
Untreated children often fail to attain early developmental milestones, develop microcephaly, and demonstrate progressive impairment of cerebral function.
Hyperactivity,
EEG abnormalities, and seizures, and severe
learning disabilities are major clinical problems later in life. A characteristic "musty or mousy" odor on the skin, as well as a predisposition for
eczema, persist throughout life in the absence of treatment.[
citation needed]
The damage done to the brain if PKU is untreated during the first months of life is not reversible. It is critical to control the diet of infants with PKU very carefully so that the brain has an opportunity to develop normally. Affected children who are detected at birth and treated are much less likely to develop neurological problems or have seizures and intellectual disability (
though such clinical disorders are still possible inclding asthma, excema, anemia, weight gain, renal insufficiency, osteoporosis, gastritis, esophagus and kidney deficiencies, kidney stones, and hypertension). Additionally, major depressive disorders occur 230% higher than controls; dizziness and giddiness occur 180% higher; chronic ischemic heart disease, asthma, diabetes, and gastroenteritis occur 170% higher; and stress and adjustment disorders occur 160% higher.
[12][13] In general, however, outcomes for people treated for PKU are good. Treated people may have no detectable physical, neurological, or developmental problems at all.