Blood Tests Performed For Newborns With Down Syndrome

[This post is a part of the “New Parent Guide To Down Syndrome” blog series. Be sure to check out the other posts!]
These are important blood test for children born with down syndrome

What do all these tests mean...?

Labs For Children Born With Down Syndrome

There will be a lot going on behind the scenes for your newborn that you may  not realize.  When your baby is away from you, they may see doctors, be tested for one of the medical concerns for children born with Down syndrome, have imaging done, have their hearing checked, or be held by everyone in the nursery because they are so cute.  If your child is in the neonatal intensive care unit (NICU), they will most likely have several more tests done then what is mentioned below.  Be sure to ask your doctor what tests were done each day and why.  You have every right to know what is going on with your baby.

There is a good chance that the nursery staff will not tell you that certain tests are done because they are so routine they assume everyone knows about them.  Your only clue may be that your baby comes back with a band-aid.  The blood tests listed below are the minimum tests expected for your newborn with Down syndrome.

[Image via iStockPhoto.]


Every child with even the suspicion of Down syndrome should have their chromosomes determined.  This is the definitive diagnosis for Down syndrome and will also be able to differentiate which type of Down syndrome your child has.

down syndrome chromosome chart

This is a blood test that cannot be obtained by a heel stick (which is the easiest way to obtain blood from a baby), but requires that  blood be obtained from a vein, like starting an IV.  You may notice that your baby comes back from the nursery with a bruise or a band aid in the bend of their elbow.  It will likely take 1 week to get the final chromosome result.

There is a quicker way to determine if there are three copies of the 21st chromosome which is done by fluorescence in situ hybridization (FISH).  This is a very specific test and will only look for specific genetic differences.   Examples are FISH for Trisomy 21, 18, or 13.  There are several other FISH tests, but your child would only have the one for trisomy 21 at first.   Since the characteristics of Down syndrome can be seen in other syndromes your doctor may want to run more tests if a FISH is negative.  The FISH test can determine a mosaic pattern, translocation, and nondisjunction.  FISH studies are usually done with the full chromosome study but will come back much sooner with results.

The results will likely look like algebra to you but they are actually quite easy to understand once they are explained.  Even if you do not understand what the results are, there should be an explanation at the bottom of the result page you receive.   Below are possible results for children with Down syndrome.  The first number is the number of chromosomes present, 46 or 47.  The second section determines if the child is a boy or girl by listing what type of sex chromosomes are present.  Either two X (girl) or one X and one Y (boy) will be present.  Last it tells you what difference is seen; is there an extra 21st chromosome, or translocation.  A typical child has chromosomes that read 46, XX (girl) or 46 XY (boy).

Nondisjunction: An extra 21st chromosome is present

  • 47 XX, +21 (girl)
  • 47 XY, +21 (boy)

Translocation:  The most common translocation is between the 14th chromosome and the 21st.  This shows that those two chromosomes have exchanged information.  You can put in other numbers for the number 14 below.

  • 46 XX, t(14q,21q)
  • 46 XY, t(14q,21q)

Mosaic:  Both typical cells and cells with three copies of the 21st chromosome were found.

  • 46 XX/47 XX, +21
  • 46 XY/47 XY, +21

Newborn Screen

Our baby just got finished with a new born screen

Getting blood drawn is hard work.

All children are required to get a newborn screen sometimes called the PKU test by people who do not realize that the tests have expanded to include other conditions.  This test is so common that nurseries frequently do not tell parents they have even done this test.  The blood is obtained by a heel stick. Your child will likely have a band-aid on their foot as proof that it  has been done.

Each state must include certain conditions but many have an expanded newborn screen.  The purpose of the newborn screen is to screen for conditions that when caught early will either save the child’s life or prevent mental retardation. However, there are also conditions included that will benefit the child if known early such a sickle cell disease and cystic fibrosis

The benefit of knowing about these conditions is so great that the cutoff value for a positive is set low enough to catch all true positives or babies that really have the disorder.   This allows for several false positives.

Noah was actually a false positive for glutaric acidemia type 1.  I am thankful that this test is in place because when this condition is caught early it can save a child’s life and protect their brain.

Why The Newborn Screen Is Important For Down Syndrome

This test is very helpful for children with born with Down syndrome because it screens for hypothyroidism or not enough of the thyroid hormone.  This condition is more common in children with Down syndrome, and the child will be screened for this throughout their life.  This test will be repeated if it is abnormal the first time, but will also be repeated after 7 days of life even if it is normal.  You will hear from your pediatrician if the results are positive, and if they are not able to get to you in time you will get a notice in the mail that a result came back positive.  If you hear nothing, do not worry as that means your results are negative.  You will need their thyroid tested again at 6 months.

Complete Blood Count with Differential (CBC with Diff)

A complete blood count with differential may or may not be done while in the hospital.  The American Academy of Pediatrics recommends that children have this done within the first month.  A CBC looks at white cells which fight infection, red cells which carry oxygen and platelets that help us clot.

I am about to use some very scary terms but I want to reassure you that the majority of children with Down syndrome do very well with these diagnoses.

There are 5 abnormalities that can be seen in children with Down syndrome.  The three most common are not harmful and typically resolve by 3 weeks of age.  These include neutrophilia, too many neutrophils a type of white cell; thrombocytopenia, not enough platelets; and polycythemia, too many red cells.  There are two other conditions that are more concerning for children with Down syndrome and they are hard to differentiate.  Transient myeloproliferative disorder (TMD) and congenital leukemia will initially look the same.  Blasts, immature blood cells, are seen in the blood stream which is not where they should be found.    TMD usually resolves spontaneously by 3 months of age and is typically only seen in newborns who have Down syndrome.

Congenital leukemia is also associated with blasts in the peripheral blood but they also invade the skin and other organs.  This diagnosis sadly has a much worse prognosis.  A child with Down syndrome will likely be watched through this course as it is much more likely to resolve by 3 months of age and be TMD.

Final Thought On Labs

Our own personal experience with lab tests has been an adventure, specifically the chromosome tests.  It is very hard to wait for these tests.  You will stare at your baby and not see what the doctors are talking about, as will most of your family.  Even as a doctor I would question the diagnosis as I looked at Noah’s little upturned eyes.  There is a good chance that your child will be doing so well that you just think it is impossible that they have Down syndrome and the risks that go along with that.

At first you will just want them to have typical chromosomes.  Then you will say if they do have Down syndrome they must be a mosaic because my child is amazing.  Despite the results your child will continue to be amazing as all you have done is proven what has been there since they were conceived.

[This post is a part of the “New Parent Guide To Down Syndrome” blog series. Be sure to check out the other posts!]

Yes, even a blog has to have fine print these days.  Here is ours: disclaimer: This post was written by my amazing wife, and the mother of a child diagnosed with Down Syndrome!  She is also a pediatrician, but not your pediatrician!  All of the information on this website (although great!) is for informational purposes only.  Nothing on this site is intended to create a physician-patient relationship, replace the services of a licensed, trained physician, or to be a substitute for medical advice of a physician or trained health professional licensed in your state/Country.  You should not rely on any of the information contained on this website, and should contact a physician licensed in your state/Country on all matters relating to your (or someone else’s) health.  You agree that you shall not make any health or medical related decisions based in whole or in part of anything contained on this website.

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About Rick Smith

Hi, I'm Noah's Dad and I'm passionate about giving the world a window into our life as we raise our son who was born with Down syndrome. I also enjoy connecting with other families, so let's stay connected.


  1. Thanks for your comments on my blog! I love the idea of your blog! I admire you for having the time to blog a video each day! I will definitely subscribe to your blog! Noah is adorable and I will enjoy watching him grow up!

    • Carlin,

      Thanks so much! Yah, it’s a lot of work, but our hope is that we can show the world minute, by minute, and day, by day that Down Syndrome is ok. 🙂

      We look forward to getting to know you through your comments on our blog, and by checking out yours.

      Best to you guys.

      P.S. You should grab a Gravatar ——>

  2. thnx for the post!we have done the PKU for Arbi which showed everything OK, but i am not sure if he was tester for the CBC!! now he is 4 months and 10 days!

  3. I am soooo glad we knew ahead of time that Jillie would be born with an abundance of the 21st chromosome.  No waiting to see, no shock and no extra blood tests (that I remember).  My issue is with labs that don’t know how to draw blood from babies with Down syndrome.  Their little veins seem tougher than most.  I had a rough time when I took Jillie in for her thyroid testing at 1yr.

  4. carole goodman says

    Wow! there is a lot to digest in this article but totally interesting and most informative. Thank you for doing this report on the blood and etc. It is really quite scary , but does make a difference if you  know, what to be prepared for.

  5. Sschuldt21 says

    Thank you for sharing your story.  My son Payton was born 2/10/11 and is the light of our lives. He is our 3rd and last and he brings us so much joy!  I love that Noah is only 2 months older, because I get to see the great things he can do and it reassures me that Payton will sit up on his own for more than 3 min., before falling back, that he will crawl and walk.  I enjoy your videos and Noah is a doll :o)

  6. Libbo263 says

    I did the same thing, Rick, We were praying for mosaic, but after finding out he had Trisomy 21 we were a little bit upset.  But now i fall in love with him more EVERYDAY!! Love Reuben so much!! 
    I would love to know Abbie’s opinion on this, Reuben’s Pediatrician said he didn’t need blood tests to check anything. He said Only if he’s not himself and you notice a difference, then  they may do blood test.  This is also the pediatrician who told me tubes in Reubs’ ears may not be the best thing for him! The way i see it, is if he can’t hear hows he going to develop to his full potential?   xx

  7. Very informative, James had so many tests…some that may have not been run but we were in a very good Children’s Hospital and they were already running things. We really didn’t understand the why of everything though.

  8. Maria Neumann says

    Great information, thank you!  Love following your blog! 

  9. I didn’t know people could do tests on babies without telling the parents this post has been very eye-opening.

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