Laboratory and Blood Tests

female doctor with preemie 
To do what's known as blood work for your premature baby, she will need to have a small sample of blood taken by either a brief prick of the heel or from a vein with a needle. Many of these procedures are painful. There are certain measures that can be taken before these procedures that can reduce pain and provide comfort. For example, sucrose, a sweet liquid, can be put on the tip of a baby's tongue and this can reduce pain from these procedures.

Premature babies do not have a lot of blood and so as little as possible will be taken for tests. Blood is drawn into small, air tight tubes which are labelled and sent to the laboratory for analysis. The procedure doesn't take a long time.

Blood work will likely be required a number of times. Initially, blood will be taken for diagnostic reasons. Following that, blood work will be done to monitor a premature baby’s progress. For example, if the first diagnostic blood test determines that a baby is hypoglycemic, meaning that he has a low blood sugar level, treatment will begin and further blood tests will be used to determine if progress is being made.

There are many different tests that can be done on blood, each giving a measure of a certain aspect of the blood itself and possibly an indication of a specific problem. In addition to blood, other bodily fluids such as urine and cerebrospinal fluid, which is the fluid within and surrounding the brain and in the spine, can be assessed in the laboratory and can give indications about a premature baby’s health.

It should be noted that some blood tests are standard and will be done whether a problem is suspected or not. Other tests will only be done if a problem is suspected.

Complete blood count

The complete blood count (CBC) is a common blood test. It measures the amount of red blood cells (RBCs), white blood cells (WBCs), platelets, and hemoglobin in the blood. RBCs carry oxygen to the rest of the body. WBCs are part of the body mechanism for fighting infection. Platelets are parts of the blood that help with clotting.

Checking hemoglobin is important, especially in babies who may be cyanotic, meaning that they have a bluish tinge to the skin, because it is the hemoglobin in RBCs that carries oxygen to all parts of the body. Low hemoglobin is a sign of anemia. Anemia occurs when there aren't enough RBCs in the body, which means the heart must work harder. The body may also get less oxygen, and so has less energy. Anemia can be treated by taking iron supplements or through a blood transfusion.

Other blood tests

In addition to counting WBCs and RBCs, other common tests on the blood are likely to be performed. These include tests for blood gases, electrolytes, and glucose.

The blood gases test gives information about how well the baby is getting oxygen into the bloodstream and getting rid of unwanted gases such as carbon dioxide and other waste products. This test can recognize acidosis, which is an increased level of acid in the blood. This is usually due to respiratory problems whereby the lungs are not expelling enough carbon dioxide, disturbing the acid balance of the blood. Acidosis can also due to metabolic reasons, such as a failure of the kidneys and other organs that regulate the level of acid in the blood.

  • Analysis of glucose or blood sugar is a common blood test. The glucose in the blood provides energy for the body and brain. The level of glucose in the blood shows if the baby is getting too little or too much energy from intravenous fluids and/or milk.
  • Electrolyte tests measure minerals such as sodium or salt, potassium​, and calcium in the blood. Additional minerals in the blood can be analyzed but are done so less frequently..
  • Infection can often be detected with blood tests.
  • Bilirubin, an excess of which causes jaundice, can be detected with a blood test. Additional testing will determine if the jaundice is being resolved.
  • Coagulation tests can determine how quickly the blood coagulates.
  • Renal and liver function tests are used to determine whether the kidneys and liver are functioning properly.
  • Chromosomal testing can determine if the baby has a genetic abnormality.

Examination of umbilical cord and placenta

Your premature baby’s umbilical cord and the placenta are also checked as a regular part of the physical assessment. The umbilical cord usually contains two arteries and one vein.

A sample of your baby’s umbilical cord will be taken to determine her hemoglobin level and ABO blood type. If the umbilical cord is not available to do these tests, they will be done on the baby’s blood. It is important to determine whether your baby had any blood group incompatibility with her mother during pregnancy because blood group incompatibility is associated with jaundice in newborn babies.

Testing other body fluids

In addition to testing your baby’s blood in the laboratory, cerebrospinal fluid and urine may also be tested.

Cerebrospinal fluid testing may reveal infection, most commonly meningitis. The fluid is taken in a procedure called a lumbar puncture or spinal tap.

Testing urine may reveal infection. Glucose and protein levels in the urine can provide information about kidney function.

Kim Dionne, RN, MN, NNP