Why Do Preemies Need Blood Gas Tests?

Blood gas tests can tell your baby's doctor a lot

Preemie Baby

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A blood gas is a blood test that looks at the acid and base balance and oxygenation level in a newborn's blood. Blood gasses are some of the most common blood tests used in the NICU, as they pack a ton of information about your baby's health into just a few drops of blood.

In the NICU, you may hear blood gasses being called many different names. A blood gas test can be called an ABG, for arterial blood gas; a CBG, for capillary blood gas; or just gas. Other NICUs may have other terminology.

NICU staff collects blood for blood gas in different ways. If your baby has an umbilical artery catheter (UAC), blood can be drawn from the UAC without having to prick your baby. Blood gasses can also be collected with a heel prick or by inserting a needle into one of your baby's arteries or veins.

Understanding Your Child's Results

When your baby has a blood gas, the NICU staff can learn a lot from the results. These results might include:

  • pH: Your baby's acid and base balance are measured by the pH. A low pH means that your baby's blood is acidotic, whereas a high pH means their blood is alkaline. Both conditions can be dangerous.
  • Carbon Dioxide: Carbon dioxide can build up in your child's blood when your baby is not breathing well, which can cause acidosis. Doctors can lower carbon dioxide levels by making sure your baby's airway is open or by increasing respiratory support. For example, a baby with a high carbon dioxide may need to be placed on CPAP or have their ventilator settings changed.
  • Bicarbonate: Bicarbonate, or bicarb for short, is a measure of your baby's metabolic functioning. A high or low bicarb can be caused by sepsis; prolonged lack of oxygen; or problems with the heart, kidneys, or gut.
  • Oxygen Saturation: An arterial blood gas measures how much oxygen is in your baby's blood. Blood gasses drawn from a vein or from a heel prick are not good measures of oxygenation.

All blood gasses look at the measures listed above, however, some tests may look at other measures of your baby's health in the blood sample including glucose level, electrolytes, and hematocrit.

Why Do Preemies Need So Many Blood Gasses?

If your baby is in the NICU, you may find yourself worrying over how many bloods tests your baby is getting. Doctors and nurses worry about it too! Too many blood tests can cause anemia, especially in preemies who have less blood, to begin with.

Frequent blood gasses are common in the NICU, but for good reasons. It's important to make sure that babies are getting the very best respiratory support, especially since preemies are very sensitive to even small changes in ventilator settings and oxygen levels.

The blood draws won't hurt your baby if he or she has an umbilical artery catheter or an arterial line. If blood gasses must be drawn via the heel stick, the NICU staff will be very gentle and will combine blood tests to minimize the number of painful procedures your baby needs.

3 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Gleason C, Juul S. Avery's Diseases of the Newborn (10th Edition). Elsevier. 2017.

  2. Linden DW, Paroli ET, Doron MW. Preemies - Second Edition The Essential Guide for Parents of Premature Babies. Simon & Schuster. 2010.

  3. Strauss RG. Anaemia of prematurity: pathophysiology and treatment. Blood Rev. 2010;24(6):221-5.  doi:10.1016/j.blre.2010.08.001

Additional Reading
  • Karlesen, K. (2006) The S.T.A.B.L.E. Program Learner Manual (5th ed).
  • Newborn Emergency Transport Service. "Blood Gas Interpretation." Neonatal Handbook.
  • UCSF Children's Hospital. (2004) "Acid Base Balance." Intensive Care Nursery House Staff Manual.

By Cheryl Bird, RN, BSN
Cheryl Bird, RN, BSN, is a registered nurse in a tertiary level neonatal intensive care unit at Mary Washington Hospital in Fredericksburg, Virginia.