PKU Test Results — What’s normal?


Ok my son was born six weeks ago. He was in the hospital for 10 days because he had a fever of 104 on the second day. He was tested for his PKU on the seventh day. Last week the hospital called and said they wanted to retest him because his PKU came back a 4...they said 4 was in range but that four or under was normal so why test again? We took him back and did the test again and are waiting for the results. Now Im reading up on PKU and I'm worried sick because it all says to change their diet right away and he is already six weeks old and I'm not sure how long it will take to get the results back again. They didn't know last time for four weeks. He is a breastfeed only baby. We are from Fla but live in Puerto Rico. That baby is blonde with blue eyes so that worries me too since they seem to have that problem more than darker skin and eyed babies. I have read too that some other states and countries have the standards different. Some have 2-6 as normal. In that case he would be fine. Some say 2 or below. I just don't know what to think. My doctor here isn't a lot of help. It seems he doesn't know a lot about it. Is there anything I should do while I wait for results as far as his diet? Am I taking chances breastfeeding him since there is protein in my milk? What do babies normally test at in the states? I don't know if this has anything to do with it but I read that peanuts have high levels of phenylalaine in them and I ate some in the hospital before breastfeeding before he had the test. Not many but I did eat them. Anything you can tell me that would put my mind at ease would help. Thank you!

Dr. Greene's Answer

The PKU test is a screening test for PHENYLKETONURIA (PKU). The normal values of the test depend entirely on the laboratory where the test is run, and the methods and units used. In some cases the number can be normal up to 20; in others, anything above 1.2 is abnormal. You will not know about your son’s values without checking on the normal ranges of the lab.

The PKU result may have only been an artifact of having to delay the newborn screening test. Your eating peanuts doesn’t change the situation and didn’t make your son sick. Positive and borderline tests are routinely rechecked. The PKU test is a screening test-not a diagnostic test. It simply identifies which kids should be tested, not which have PKU. Most children with a positive screening test do not turn out to have the disease.

PKU is a disorder caused by a missing or decreased enzyme called phenylalanine hydroxylase. Phenylalanine is not properly processed by the body. When there is too much phenylalanine in the diet, the substances that build up in the blood can gradually cause brain damage.

Babies with PKU are normal at birth. If phenylalanine is not restricted, the damage is gradual, with the IQ dropping about 4 points per month. But if untreated for a year, the baby has lost almost 50 IQ points, resulting in severe mental retardation.

In babies with PKU, vomiting, sometimes severe, is often present as a symptom. The muscle tone is often unusual. About 1/4 of children with PKU have seizures, and most have poor growth of the body and head. These babies have fair skin, blue eyes, and hair that is blonder than that of their siblings. These children have an unpleasant musty or mousy odor from the excess by-products of unprocessed phenylalanine.

Treatment for PKU is a low-phenylalanine diet (but not TOO low-even children with PKU do need some). Human breast milk is fairly low in phenylalanine content. The ideal for most infants with PKU is to be partially breastfed (so that the benefits of breastfeeding can be obtained), while adjusting the diet appropriately. Babies receive a measured amount of Phenylac (phenylalanine-free milk) and an adjusted amount of breastfeeding. Phenylalanine levels need to be monitored. Alternatively, Ross (the maker of Similac) also makes a complete formula for PKU called Phenex.

As kids get older, the dietary restrictions can be tough on them and on the family. It’s important to have emotional and practical support from experienced people. Although the benefits of dietary therapy are most evident during the first 6 years (and when a woman with PKU gets pregnant), it is wise to continue the diet throughout life. It can prevent problems with thinking, remembering, and problem solving. In the past, the benefits of continuing the diet beyond early childhood were not clear. We now know that if a child or adult has stopped the diet, it is never too late to go back on. Most who do retun to the diet think and feel better, with measurable improvement in attention span, concentration, and memory.

At this point you don’t know that your child has PKU at all. You do know that the wonder of having a newborn was interrupted with the terror of having to deal with a high fever and prolonged hospitalization. Then, when things had settled down, you heard about this PKU issue!

And now you have to do one of the hardest things for parents: wait. Waiting to see if your son is healthy. In the meantime, you might want to be in touch with whatever doctor would manage the situation if your son were to prove to have PKU-that doctor should be able to give you the best advice for right now. Follow-up tests are usually done far more quickly than the routine screening, so even though the wait may seem like forever, you shouldn’t have to wait long.

Note: We received the following response from Nicole to the above article.

Thank you Doctor! Your answers helped us a lot. We called the lab and they said 4 is borderline on their scale and that’s why they wanted to retest. They say they might have the results as early as tomorrow. You are right that is the hard part… waiting. He seems so healthy and happy and he is smiling now. He has none of those symptoms. He spits up some but he’s not vomiting and has no strange smell. The lab said the same [thing you did] that most of the time they retest the results come back fine. Its so amazing the way the internet brings us all together. Thank you so much for your time. What a special service you provide.

Last medical review on: April 24, 2008
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Dr. Greene is a practicing physician, author, national and international TEDx speaker, and global health advocate. He is a graduate of Princeton University and University of California San Francisco.
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Recent Comments

Until about 12 years ago I did not know I had PKU. Most of my doctors don’t know about PKU. Even some Pharmacists do not know about PKU. I have taught them what I know. The pharmacist that have graduated recently know what PKU is. Also, my doctors do not talk to each other. I have been given medicines that I shouldn’t have because they have polysorbate in them or are coated with artificial sweeteners.

I only found out I have PKU because I had allergy testing done. My mother definitely had PKU, but she was never tested for it. She had a lot of the symptoms I had. And I was not tested as a baby, as I was born in 1949.

When I watch my diet, I feel one percent better. I am able to lose weight. I feel healthy. I have better concentration. My memory is much better and the best thing is I am not depressed. Once I go back to my old eating habits, I go into a downward slide. I also have to be careful of all my medications, even over the counter kind.

Thanks for letting talk about how I am feeling living with PKU.

what is the normal range of PUK?

My grandson is 9 days old. He was tested for PKU second day after birth. The hospital called us on the 6th day and asked us to come in for another blood test. Still waiting for the results tomorrow.
The blood test revealed 360, which as we were told is 6.
They think I may go higher.
Should we go for a third test? I feel the second blood test was too early?


Is there any link to abnormal PKU due to alcoholism

I was tested for phenyl and it was at 73 while fasting, what does that mean? I live in Canada and not sure if I tested positive when I was first born or not but suffer the symptoms.

Hi my nephew has Pku. His is 32 years old and he has been off of his diet for Im not really sure how long because he was not living around us to keep check on him. We now have him living with us and trying ti get him help and back on his diet. He has no ins at this time and I really don’t know what to do. Can anyone tell me of a place in S.C that will be willing to help him get back on his diet and help him with his anxiety?

Hi Linda. I’m an adult with PKU. I’m also a professional videographer. Over the last few years I’ve been producing a series of videos for the National PKU Alliance ( They are the leading PKU non-profit in the US, and a great resource of information. Anyway, the subject of adults being off diet is a complex one. I’ve been on diet all my life for the most part, although there was a period of time I was a bit too relaxed with it. I used to think it was very simple issue, people being off diet. But after meeting hundreds of others with PKU, I’ve learned there are many reasons why someone goes off diet. I would never, never criticize or judge someone who is off diet, but the truth is that being on diet for life is essential for someone with PKU. Here is a video I recently produced, that shows some of the possibilities when someone goes off diet: I hope this helps. If your nephew likes, he can connect with me on Facebook: Social media has become a great tool to connect with others with PKU. If he wants a support system of others who also have PKU, I can help him get connected. Just send me a message on my Facebook page. Please tell your nephew I said to not give up. Me and my many other PKU adult friends out there are here to help if he wants help.

I’m wondering 1069 am 1362 are a normal range for a 2 month old? I’m really lost because my teenager became a father an it’s no where in our whole side of the family that we know of an from what I’ve learned we would know if someone had it an wasn’t dieting properly.
The issue is we haven’t been able to talk to any of the specialists caring for jace an can only learn from the mother an grandmother. To make it harder we have Ben lied to about many things and are really trying to get paternity established so we can get the info from his providers. The nurse said his levels were the numbers I asked about. However his mother told me he was an 8.
I also don’t know how severe or what level he has.. Mild or ..I’ve read there’s a few kinds

All 3 of my children have PKU . Thankfully my two older girls have no diet restrictions because they’re levels never elevated past 6… Currently waiting on the second heel stick result for my two week old. My newborn daughter’s results were 2.6. Praying for another non diet restricted child.

Hi. My baby is 1 month old and has had 4 blood tests to check her digestion of protein. They said it was elevated to 150 (or 6) on the scale. We just had the 4th blood test yesterday (waiting for the results). They said if it is still elevated they would send us to a specialist. Is 150 (or 6) very high?

if a phe level is high but you do all the right things to bring it down,how long should it take to see
a lower phe level? grandson is 51/2 and 32 lbs.

I was born with pku so i know exactly how hard it is to be on a low phe diet. When i was born in England they weren’t doing the test. So I wasn’t diagnosed till the age of seven. As a result, I have had a lot of difficulties learning and went to a special school. I encourage anyone going thru this to keep trying to get help because having a child with pku isn’t easy, but the low phe diet really helps. The pku child to be able to function in the world.

Hello to everyone
I am Ahmed of Palestine Medical Laboratory Technician Work
I have a year-old girl is now eighth months
Was an examination of the heel
In the first week after birth was the result =4.2
The re-examination after two weeks result =4.38
The giving Formula milk was take two tablespoons with sixty-mm water
It was re-examination every month
The result has been reduced to=3
After a month to result = 4
After that, give it three spoons milk with ninety 90 mm water
All outstanding milk with thirty-mm water
The result fell to =3.3
A month later rose to =4.8
next month = 2.9
Was now = samples may be result after 4 days i wait
A new sample was withdrawn and the result did not look so far we are waiting
Health screening
There is no examination of the enzyme in all of Palestine

My daughter is 2 weeks old and has been tested for PKU twice. First time they did a test in hospital after 24 hours and said result is positive. Doctor wanted us to retake test after a week and the results came in today and said she is boderline . Doctor wants us to retake test again and see if the levels go down further. She is 2 weeks old as of today. Is it really true that pku level can go down within first few weeks and is it possible that she would be normal? We are just worried if our doctor is just trying to assure us or it is the reality.
Worried sick waiting for results ….baby seems to be fine otherwise with everythng normal.

There are several reasons why some infants may have an elevated phe on newborn screening – such as immaturity of the enzyme called HPPD and utilization of TPN (total parenteral nutrition). So repeat the tests later may eventually give you negative results. If the data is still inconclusive, ask your doctor about genetic testing for PAH and DHPR genes.
Good luck!

So taking my 4 month old back in for the third time because they said her test was inconclusive again I asked if anything was to high or low and they it just showed inconclusive any ideas what is going on…she seems to have nothing wrong with her?? Concerned

When they did the test the blood cud have been smeared and could have inconclusive. BC of that…. I have a 7 year old that was tested 3 times….. But did not have to wait long for the results… But I myself have pku and I know what its like to have to live wit it and I know how hard it was on my parents. 2 find out 3 weeks after I was born…. And they had to take me to a hospital that was 2 n a half hours away so I could start the treatment…. The doctors. Told my parents that I was the 85th case in the us that had been diagnosed with this genectic disorder.

My great grand son is on the way to the hosptal for re-testing. He is only 10 days old. He has trouble with his kidneys. Thank you for this web sight. It helps me to have hope that this will pass. If not, God will give us strength to do what we have to do.