Newborn Screening Test Positive? It May Be A False-Positive!

Last Updated: Aug 23, 2023

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To best prepare ourselves for the arrival of our daughter, my wife and I took a few baby and parenting classes, we read books on the subject and researched the internet. The amount of information (and misinformation) available to new parents today is incredible, so we had to be selective and hence didn’t pay too much attention to stuff that could go wrong, including diseases and complications. With no family history of major disorders or genetic defects, we figured chances are, that everything is going to be just fine.

We were, however, aware of common procedures and issues with newborns such as:

Common Procedures

  • Newborn hearing test (to make sure the baby’s hearing is OK, which is important for speech development)
  • Newborn screening test (to catch genetic or metabolic diseases early)
  • Vitamin K shot (to help with blood clotting until the baby’s Vitamin K production kicks in)
  • Antibiotic eye ointment (to prevent infection caused by bacteria in the birth canal)
  • Initial assessment of babies vital functions at 1 and 5 minutes after birth to determine the APGAR score (named after Dr. Virginia Apgar)

Common Issues

  • Elevated bilirubin levels (Jaundice or yellow coloring of the skin caused by immature liver)
  • Other minor skin defects (pimples, spots…)
  • Hair-growth on body parts other than head (it’s called lanugo, is completely normal and disappears after a few weeks)
  • Enlarged genitalia (due to mom’s hormones passed on to baby)

Every time I read something like “some babies may have XYZ condition (i.e., jaundice)” I naturally assumed that only applies to other babies, but not ours. So I set myself up for a surprise!

Newborn Screening Test

According to Baby’s First Test:

Newborn screening is a state public health service that reaches each of the more than 4 million babies born in the United States every year. It ensures that all babies are screened for certain serious conditions at birth, and for those babies with the conditions, it allows doctors to start treatment before some of the harmful effects happen.

Newborn screening is performed soon after the birth of your baby, and in most cases, while you are still in the hospital. All it takes is a few drops of blood and a simple hearing test.

In “Baby 411: Clear Answers & Smart Advice For Your Baby’s First Year” we read that the pediatrician is unlikely to discuss the test results unless at least one of the tests is positive. So we expected not to hear anything about newborn screening anymore after our baby’s blood was drawn at the hospital, one day after birth.

During the first week of our daughter’s life, we had appointments at our pediatrician, Dr. Michael Papciak and Dr. Rebecca Clements of Preston Ridge Pediatrics (who I can highly recommend), almost every day to check and make sure her weight went up and her bilirubin levels went down. Jaundice, caused by elevated Bilirubin levels causes newborns to be sleepier than usual, so they may not eat as much as they should and thus lose more weight than normal. Both checks went according to plan, but on day ten the pediatrician ordered an extra blood test and a second newborn screening test. He told us not to worry but explained that one of the newborn screening tests was positive. He elaborated that her 17-OHP levels were elevated, which triggered the test for Congenital Adrenal Hyperplasia (CAH) to be positive.

Newborn screening test positive? Stay calm, it may be a false-positive!

Congenital Adrenal Hyperplasia

I had never heard about such as disease and asked Dr. Papciak for a copy of the test report so I could do some research. We were still at the pediatrician when I googled for CAH. The first hit was a Wikipedia article that summarized CAH as:

Congenital adrenal hyperplasia (CAH) refers to any of several autosomal recessive diseases resulting from mutations of genes for enzymes mediating the biochemical steps of production of cortisol from cholesterol by the adrenal glands (steroidogenesis).
Most of these conditions involve excessive or deficient production of sex steroids and can alter development of primary or secondary sex characteristics in some affected infants, children, or adults.

A genetic disorder involving sex steroids resulting in potentially altered sex characteristics (ambiguous genitalia ring a bell?)? I suddenly felt like hit by a train, and I wasn’t sure if and how I should tell my wife what I just learned.

Back at home I started doing some more research and learned that the most common form of CAH is caused by 21-hydroxylase (an enzyme) deficiency. Within this particular form there are three different types of CAH, which vary by severity level:

Salt-wasting CAH (classic form)

This is the most severe and common form (75% of patients affected by 21-hydroxylase deficiency have this form) and can lead to death within weeks, caused by the body excessively waste certain electrolytes. That’s why our pediatrician had our daughter’s Potassium, and Sodium levels tested right away. Since the levels were normal and she didn’t show any of the other symptoms (vomiting, lethargy…) we concluded that she was very likely not suffering from this form of CAH.

Simple Virilizing CAH  (classic form)

This form of CAH is less severe and typically manifests itself in ambiguous genitalia (girls may have an enlarged clitoris that looks like a penis), excessive hair growth, etc. Despite not being life-threatening it can lead to accelerated growth, but since the epiphyses fuse early, affected patients are often of a short stature; infertility and other issues.

We were told in the hospital as well as by our pediatrician that our daughter was physically OK (i.e., no penis and normal hair growth) but given the positive newborn screening test I couldn’t help but relate the hair on her back (lanugo) and her slightly enlarged genitalia (both normal for a newborn) to CAH. I even read a study about “Penile and Clitoral Sizes of Normal Full-Term Newborns in Korea” (I couldn’t find an equivalent study for newborns of Hispanic/Caucasian descent) to make sure our daughter’s genitalia was within normal range. It turned out to be within normal range, which meant she could only have a very mild form of Simple Virilizing CAH.

Late-onset CAH (non-classic form)

Late-onset CAH is the mildest form and as the name implies it sets on later in development and doesn’t necessarily and immediately affect newborns.

The more research I did, the more it became clear that reliable testing for CAH in newborns is not a simple task and the false-positive rate is quite high. Even Baby’s First Test points out that: “It is important to remember that an out-of-range screening result does not necessarily mean that your child has the condition.” Dr. Philip M. Farrell, a professor of pediatrics and population health sciences at the University of Wisconsin School of Medicine and Public Health estimated that 1 in 50 [newborn screening] tests are false-positives but for the disorder Congenital Adrenal Hyperplasia, there are between 100 and 200 false positives for every child truly affected.

That’s quite a high false-positive rate, and it gave us hope that our daughter’s test, too is a false-positive. To get more information about test procedures in Georgia I sent an email to Joanna Pringle, a Program Consultant at the Newborn Screening Unit of the Georgia Department of Public Health and she called me back within a few hours. She also forwarded my email to Angela Wittenauer, a Registered Nurse at the Genetics Lab of Emory University. She too called me back and confirmed that there are false-positives and that there is no need to be worried and we should wait for the results of the second test.

The negative result

About two weeks after the pediatrician sent in the blood sample for the second test we got the good news that the second test was negative and hence the first test was a false-positive caused by high cortisol levels in our daughter’s bloodstream a day after birth. The elevated cortisol levels were most likely caused by stress during delivery. Who knew that the delivery process was stressful for the baby :). Other reasons for a positive test result could be prematurity (preemies have naturally higher levels of 17-OHP) or simply a false-positive.

Bottom line: Every newborn is different, and a positive newborn screening or a failed hearing test may not mean anything. So stay calm, enjoy the nightly feedings and diaper changes and wait for the second test before freaking out!


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10 thoughts on “Newborn Screening Test Positive? It May Be A False-Positive!”

  1. Thanks for sharing this! We just got the call from the pediatrician that our 2,5 week old needs to be re-tested for PKU disorder :( Im devastated and cant keep myself from thinking about what this disorder would do to our seemingly perfect little girl. I pray it turns out to be a false positive!

  2. After I was called and informed my little one tested positive for Biotinidase deficiency just 5 days into her new life…. my heart dropped and I just wanted to crawl in a hole. So much went through my mind and trying to cope with a newborn as first time parents. I ended up researching and learning so much about this disorder that most doctors who practice 45 years never came across. I knew more about it then any doctor I spoke to. We were told to bring the little one to have her tested to confirm at Sick Kids in Toronto. The results will come in 2 weeks. The wait in those two weeks was stressful. Little redness or spots on the baby had me going nuts…. thinking it is signs and symptoms. Finally the test results came back and my little one was a false positive. No further follow up needed and instantly discharged by Sick Kids. I felt like I won the lottery. So for any parent who gets this positive screen call…. I know what you are going through. I did a lot of reading online and the confirmed case for all those positive calls are extremely low. Like Biotinidase which was my case. 5000 positive screen and only 32 were confirmed. You still have the odd ironically. Hope my stories help shine some hope for those going through this.

  3. We have almost the same experience when my daughter was screened! My LO is a preemie. Initially, tested positive for CAH but after 2 more repeat NBS she tested negative. It was really heart-breaking and i spent hours of searching about CAH. Thank God all is well…

  4. Thanks for writing this. It’s nice to ready about someone else going through the same thing! We just had our little boy’s retest done today. Hopefully it will be negative. He had an extra stressful birth (shoulder dystocia) so hoping that’s the reason for his positive result!

  5. Thank you for sharing this. I as well got positive results for this condition on my daughters labs but I’m very confused as she doesn’t have any of the symptoms? I’m so heartbroken. Today we had her second newborn screening sent off to the lab … Im really beside myself.

  6. Omg, this is exactly what I went through all day yesterday! I was told my preemie baby girl was positive for CAH. I googled and tried to find anything I could on it and searched for images to compare her to and was driving myself insane! I felt so many emotions and later I was told by the dr. not to worry because it was very common for preemie babies to have abnormal newborn screenings as you said. But, I’m glad I found this so I know I’m not a crazy overreacting parent! I knew it would be hard but man is this a roller coaster!!

  7. I’m waiting for the results of the second screen after my baby got a borderline positive on the first test?.He seems so healthy I’m just praying that it was a false positive.???

  8. Thank you so much for writing this. I’m waiting for the results of the second screen after my baby got a borderline positive on the first test. He seems so healthy I’m just praying that it was a false positive. They need to work on improving the ppv of these tests. It’s so hard on new moms!!!


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