How Doctors Diagnose HIE

In the first hours after birth, you may hear several different terms used by the medical team. Understanding how doctors arrive at a diagnosis of Hypoxic-Ischemic Encephalopathy (HIE) is a key part of navigating your baby’s care.

Neonatal Encephalopathy vs. HIE

It is common for doctors to initially use the term Neonatal Encephalopathy (NE). This is a broad “umbrella term” used to describe a baby who is showing signs of altered brain function, such as being very sleepy, having low muscle tone, or experiencing seizures.

HIE is a specific type of encephalopathy caused by a lack of oxygen and blood flow. Because other conditions can look exactly like HIE, doctors must use a structured evaluation to confirm the diagnosis and rule out “mimics,” such as genetic disorders, infections, or metabolic conditions ^[1][2].

The Sarnat Scale: Grading Severity

The most important tool doctors use to diagnose HIE is a physical neurologic exam called Sarnat Staging ^[3]. This allows the team to grade the severity of the encephalopathy into three categories:

• Stage I (Mild): The baby may be irritable, hyper-alert, or have slightly increased muscle tone (hypertonia). At this stage, babies usually do not have seizures and often feed well shortly after birth ^[1].
• Stage II (Moderate): The baby is typically very lethargic or sleepy and has low muscle tone (hypotonia). Seizures are common in this stage, and the baby may have weak or absent reflexes ^[4].
• Stage III (Severe): The baby may be in a coma (completely unresponsive to touch) and appear very limp (flaccidity). Reflexes are usually absent.

The Diagnostic Process

To confirm a diagnosis of HIE and decide if a baby is eligible for treatments like therapeutic hypothermia (cooling), doctors generally look for two sets of evidence:

1. Clinical Distress (Criteria A): This involves looking at the baby’s health at the exact moment of birth. Doctors check for a low pH or a high base deficit (markers of acid in the blood) in the umbilical cord blood or the baby’s first blood sample. They also consider if the baby needed significant help breathing or had a low Apgar score ^[5].
2. Neurologic Evidence (Criteria B): This is the Sarnat exam. Cooling treatment is currently the standard of care only for babies with moderate-to-severe (Stage II or III) HIE ^[5][6].

Ruling Out “Mimics”

Because some genetic mutations or metabolic disorders can cause a baby to appear lethargic or have seizures just like HIE, the medical team may perform genetic and metabolic testing ^[7].

Ruling out these “mimics” is vital because:

• Treatment differs: Genetic or metabolic conditions often require specific medications or diets rather than cooling ^[7].
• Prognosis changes: Understanding the exact cause helps doctors provide more accurate information about your baby’s future development ^[8].
• Future planning: Knowing if a condition is genetic can be important for families planning future pregnancies ^[7].

Later, usually between day 4 and 10, an MRI will be used to look at the brain’s structure. This provides the “final piece of the puzzle” by showing exactly which areas of the brain were affected, helping the team plan for your baby’s long-term care ^[9].

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