Common NICU tests


Blood tests

The most common blood tests performed in the NICU are the following:

  • Arterial blood gas (ABG): This test measures the acidity (pH) and the oxygen and carbon dioxide levels in the blood. ABG is used to assess the lungs’ ability to move oxygen into the blood and remove carbon dioxide from the blood.
    These also measure the pH and the oxygen and carbon dioxide levels in the blood. However, the ABG test measures oxygen in a manner that better correlates with lung function. This is because the oxygen level of the blood in the capillaries is already depleted and on its way back to the heart and lungs. , CBG and VBG tests can still be used as screening tools for respiratory issues because the blood carbon dioxide levels are similar to those in an ABG.
  • Complete blood count (CBC): This test analyzes the components of blood, including hemoglobin, hematocrit, platelets, red blood cells and white blood cells.
    • Hemoglobin: Is a major portion of the red blood cells. It enables the body to carry oxygen from the lungs to the tissues and carbon dioxide from the tissues to the lungs to be removed.
    • Hematocrit: Is another portion of the red blood cells. It enables us to determine the percentage of red blood cells present in the body. The normal percentage will vary according to age, sex and the laboratory performing the test. Too high of a percentage can indicate dehydration, blood loss or other issues. Too low of a hematocrit can indicate anemia.
    • Platelets: Platelets are vital to blood clotting to stop bleeding. The platelet count is an important screening test of platelet function. If the platelet count is too low the patient may be prone to spontaneous bleeding that is difficult to control. Bleeding can occur in various parts of the body. If the platelet count is too high, it may indicate massive blood loss, infection or other disorders that require more testing.
    • Red Blood Cell Count: Results can be used in other tests to help diagnose a condition.
    • White Blood Cell Count: This can be an indicator of infection or inflammation in the body. The white blood cell count should be used with a white blood cell differential. The differential evaluates each of the five types of white blood cells – neutrophils, eosinophils, basophils, lymphocytes and monocytes – to give a better idea of the immune system response.
  • Electrolyte measurement: Electrolytes are the basic chemicals of the body. They include sodium, potassium, chloride, calcium and magnesium. These chemicals are essential to the function of all body cells.
  • Septic workup: These tests include blood cultures, a urine culture and a spinal tap. All of the samples are sent to the lab. Each specimen is allowed to grow and then examined under a microscope for the presence of microorganisms that cause infection. These microorganisms may be bacterial, viral or fungal. If any are found, the baby has an infection that needs to be treated aggressively with IV antibiotic, antifungal or antiviral medications. It takes 24 to 48 hours to get culture results, so to be safe, antibiotics are started as soon as the specimens are gathered and before the culture results are known.
  • Glucose (blood sugar) test: This test can be done at the bedside with one drop of blood taken from a heel stick. The blood is placed on a chemically treated strip. If the result is very high or low, a larger amount of blood may be drawn to get a more accurate measurement of the blood sugar. The amount of sugar in the IV solutions can be adjusted to keep glucose levels within the normal range.
  • BUN and creatinine tests: These tests assess kidney function. A high BUN measurement can signal kidney disease, reduced blood flow to the kidneys or other problems. A low BUN measurement can signal overhydration and other issues. The creatinine test is a slightly more sensitive test of kidney function. A high creatinine level signals decreased kidney function.
  • Bilirubin test: Bilirubin is a byproduct of the breakdown of red blood cells. The liver rids the body of this byproduct. Bilirubin can build up in the blood when the body is unable to eliminate it — either because too much is being produced or the liver is not mature enough to keep up with the amount being made.

Urine tests

A newborn’s kidneys are very sensitive to changes. Some changes that can alter urine production include: 

  • Increased or decreased blood pressure
  • A change in blood volume
  • An infection
  • A change in the pH of the blood
  • A change in the electrolyte or glucose levels in the blood

A urine test can screen for some of these issues.

Weight monitoring

Babies are weighed nearly every day. If a baby is gaining too much or too little weight, staff will conduct other tests to rule out an infection or other health issues. They will also review the baby’s calorie intake. Optimal calorie intake depends on the baby’s weight, and adjustments need to be made as the baby grows. As the baby begins to eat by mouth, staff will adjust calories received from the IV solution to balance the calories received from food. They also consider the amount of fluids that the baby consumes. Calories can be added to breast milk and/or formula, so the baby gets the same amount of calories in a smaller amount of fluid.


An X-ray uses invisible energy beams to produce images of internal tissues, organs and bones on a special plate, which is similar to camera film. This plate then sends the images to a computer.

X-rays are performed for a variety of reasons, such as:

  • Determining the optimal placement of various tubes
  • Measuring the size and shape of the heart
  • Detecting lung problems
  • Assessing general bone structure
  • Detecting stomach and intestinal problems

Although X-ray involves exposure to radiation, the amounts of exposure are controlled and monitored closely. Unnecessary X-rays are avoided. If the genitals are within the area of exposure, they are covered with a lead shield.


An ultrasound uses high-frequency sound waves and a computer to create images of soft body structures, such as tissues, organs and blood vessels. A transducer, which looks like a microphone, is attached to the ultrasound machine. The technologist performing the ultrasound gently moves the transducer over the child’s skin. The machine takes pictures and saves them to a computer so the doctor can review them later.


An echocardiogram is a procedure that assessed the heart’s structures and function. A small probe called a transducer is placed on the child’s chest and sends out ultrasonic sound waves at a frequency too high to be heard. When the transducer is placed on the child’s chest in certain locations and at certain angles, the ultrasonic sound waves move through the skin and other body tissues to the heart tissues, where the waves bounce (or "echo") off the heart structures. The transducer picks up the reflected waves and sends them to a computer. The computer translates the “echoes” into an image of the heart walls and valves.

CT (computed tomography) scans

While a regular X-ray shows a lot of useful information, it cannot provide specific details about internal organs and other structures. A CT (computerized tomography) scan provides much greater detail than a regular X-ray.

With a CT scan, an X-ray beam moves in a circle around the body. This allows for many different views of the same organ or structure. The X-ray information is sent to a computer, which interprets the data and displays it in two-dimensional form on a monitor.

MRI (magnetic resonance imaging)

MRI (magnetic resonance imaging) uses a large magnet, radio waves and a computer to produce detailed images of organs and body structures. Unlike X-rays and CT scans, MRI does not use radiation. There are no known harmful effects from having an MRI scan.