Blood Tests in Neonatal Care

Why so often

Bliss puts the rationale simply: blood does many jobs, so blood tests show how a baby is progressing, and tests let the team see how a baby is responding to care and decide whether to continue a treatment, try something new, or move a baby to a different hospital for more specialist care. In a preterm baby those questions get asked again every few hours in the early days, which is why the sampling feels relentless.

Bliss also states that tests and procedures are only done when a baby needs them, and that staff will always try to reduce pain, discomfort and disturbance. If the frequency looks arbitrary from a chair beside the cot, it is reasonable to ask what a particular test is being repeated for.

Where the blood comes from

Bliss notes that most samples are taken by pricking the skin to get blood from the back of the hand or the heel. Babies with an umbilical arterial line have samples taken from the line instead, which is one of the quiet advantages of that line and part of why it is used early. Larger samples, or blood cultures, may need a small needle into a vein.

Blood gases

Bliss explains that as well as carrying oxygen from the lungs, blood carries carbon dioxide back to be breathed out, and that measuring carbon dioxide and other waste chemicals shows how a baby is breathing and how other organs, such as the kidneys, are working. "The gas is better" usually means the carbon dioxide has come down or the acid level has improved, and it is one of the main things ventilator settings are adjusted against. NICE guideline NG124 sets target carbon dioxide ranges for ventilated preterm babies, which is why the number gets acted on rather than just recorded.

Infection markers

Bliss explains that white blood cells fight infection, that C-reactive protein rises with infection, and that checking these levels helps show whether a baby is fighting an infection or one is starting. Blood cultures are sent to the laboratory and take about 48 hours to grow, which is why antibiotics are often started immediately and stopped at 48 hours if the cultures are clear. That sequence — treat first, confirm second — is deliberate, because infection moves fast in preterm babies.

Haemoglobin and platelets

Bliss describes haemoglobin as the chemical that carries oxygen, and explains that if a baby does not have enough red blood cells the body may not get enough oxygen, which is anaemia. Platelets control bleeding and can run low in preterm and sick babies, which is why the count is watched.

Blood sugar

Bliss explains that this test shows whether blood sugar is being properly controlled, and notes that babies born to mothers with diabetes and babies with a very low birthweight are monitored more closely because they may have trouble keeping a healthy level. In late preterm babies, pre-feed sugars for the first day or two are routine, and frequent feeding is usually the treatment.

The problem nobody warns you about

Taking blood costs blood. Bliss says it directly: sometimes a baby needs multiple samples over a short period, and this might mean they need a transfusion to replace the blood used for testing. That is a genuinely common reason for a transfusion in a very preterm baby and it is not a sign of a new illness. It is also why teams batch tests where they can, use the smallest tubes available, and stop repeating things as soon as the picture is stable.

What you can do while it happens

This is the part parents most often do not know they are allowed to do. Bliss says that during procedures you may be able to comfort your baby to reduce discomfort, through comfort holding — cradling their hands and feet — skin-to-skin, or a dummy with some expressed milk. NICE NG124 separately tells staff to explain that non-nutritive sucking is beneficial and can even shorten hospital stay in tube-fed babies. These are recognised comfort measures with real effects, not distractions.

You do not have to stay for procedures if you would rather not, and units are used to both choices. Saying "I would like to be there for heel pricks" once is usually enough for it to become the norm at your cot side.

When the testing slows down

The frequency falls in steps that track the rest of the admission: fewer gases once your baby is off a ventilator, fewer infection markers once antibiotics stop, fewer sugars once feeding is established. If it feels like nothing is changing, ask which tests have been dropped in the last week. It is often the clearest evidence of progress on the chart.

Other samples that are not blood

Not everything sent off is a blood test. A urine sample may be collected with a small pad in the nappy, and swabs from the nose, throat or skin are used to screen for bacteria. Bliss also describes lumbar puncture, where fluid from around the spinal cord is taken and tested when doctors are worried about meningitis: your baby is held gently curled on their side, a nurse watches them closely throughout, and expressed breast milk is offered to ease discomfort.

Each of these is done for a reason somebody can state in one sentence. Asking for that sentence is reasonable and takes ten seconds.

Reading a result without a medical degree

You will not be handed numbers to interpret, and it is not your job to. Three habits help anyway. Ask for the direction rather than the value, because "is the CRP going up or down" tells you more than the figure. Ask what the team would do if it changed. And be wary of comparing your baby's results with another baby's on the same unit: targets in neonatal care are gestation-specific, and two babies four weeks apart are not on the same scale at all.