Understanding Your Laboratory Test: What It Is, How the Sample Is Collected, and What Your Results Mean for Your Health

Published: August 9, 2026Updated: August 16, 2026

A test that measures the acid-base balance in blood taken from the umbilical cord after birth to assess the baby's oxygen status.

Quick summary

{"Base excess measures how much acid is in the baby's blood at birth","Negative values indicate the baby may have experienced oxygen deprivation during labor","This test helps doctors determine if the newborn needs special care","The sample is taken from the umbilical cord immediately after delivery","Results are part of cord blood gas analysis along with pH and other measurements"}

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC: 28639-3
Short code: Base excess BldCoV Calc-sCnc
Synonyms: Base excess BldCoV Calc-sCnc
Category: chemistry
Sample: whole-blood
Container: Lavender-top (EDTA)
Units: N/A
Fasting: false
Population: adult
Sex: all
Age range: 18–65 years
Method: calculated
Specimen volume: 3 mL
Stability: Room temperature: 4h, Refrigerated: 24h
Hemolysis max: 0
Lipemia max: 0
Icterus max: 0
TAT: 4–24 hours
Order: routine

The base excess test measures the amount of excess acid (or base) in the baby's blood at the time of birth. It is calculated from the venous cord blood sample, which is blood taken from the umbilical cord vein right after the baby is delivered. This test is part of cord blood gas analysis, which provides important information about the baby's condition at the moment of birth.

How is the sample for this test collected, and what should I expect during the process?

Immediately after your baby is born, the healthcare provider clamps the umbilical cord in two places and cuts it. A small sample of blood is then drawn from the cord vein using a needle and syringe. This sample is sent to the laboratory for analysis. The procedure is quick and does not cause any pain to the mother or baby.

What do the results of this test mean for my health and my next steps in care?

Base excess is measured in millimoles per liter (mmol/L). A normal base excess value typically ranges from -10 to +10 mmol/L. A negative value (metabolic acidosis) suggests that the baby's blood is too acidic, which may indicate that the baby did not receive enough oxygen during labor or delivery. The more negative the value, the more severe the acid buildup. Your healthcare provider will interpret this result along with other cord blood gas values to determine if any intervention is needed.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Cord blood base excess is primarily used to assess fetal well-being during labor and delivery. It helps healthcare providers determine if the baby experienced hypoxia (low oxygen) or metabolic acidosis during the birthing process. This information is crucial for making decisions about newborn care, such as whether the baby needs additional monitoring, respiratory support, or admission to the neonatal intensive care unit (NICU). The test is particularly important for babies who show signs of distress during labor or have abnormal heart rate patterns.

In legal and medical contexts, cord blood gas analysis, including base excess, may be used as evidence in cases where birth injury is suspected. It provides objective data about the baby's condition at the exact moment of birth, which can help determine whether oxygen deprivation occurred during the delivery process.

Frequently asked questions

Is this test harmful to my baby?

No, the blood sample is taken from the umbilical cord after the baby is born. This does not cause any harm or pain to your newborn. The cord is usually already clamped and cut before the sample is collected.

Why is base excess important if the baby looks healthy?

Even if the baby appears healthy at birth, the base excess value can reveal subtle oxygen deprivation that may not be immediately visible. This information helps healthcare providers monitor the baby more closely in the first hours after birth and plan appropriate care if needed.

What happens if the base excess is abnormal?

If the base excess shows significant metabolic acidosis, your healthcare team will assess your baby carefully. This may include additional physical examination, monitoring of vital signs, and possibly other tests. Some babies with abnormal cord blood gases may need observation in the nursery or transfer to the NICU for further evaluation and care.

Can I request cord blood gas analysis?

Cord blood gas analysis is typically performed automatically in cases of high-risk deliveries, when the baby shows signs of distress, or if there are complications during labor. Your obstetrician or midwife can provide information about whether this test is recommended for your specific situation.

Sources

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy