Most children go for years without needing a blood test, and that is exactly how it should be. When one is suggested, it is usually because a doctor, nurse or therapist wants an answer to a specific question: why a child seems unusually tired or pale, or whether a restricted diet is giving them what they need. This guide to blood tests for children explains the four tests that come up most often in that conversation, what each one measures, and how sample collection works.
Why blood tests for children are read differently
A child is not a small adult, and neither are their blood results. Many markers change with age, growth and puberty, so a value that is ordinary at six may be unusual at sixteen. A review from the CALIPER project, which built age and sex specific reference intervals from healthy children and adolescents, points out that laboratories have often had to report children's results against adult ranges because good paediatric data were missing (Adeli et al., 2017). The practical lesson for parents is simple: a result should always be interpreted by a professional who knows the child's age and history.
Iron is the clearest example of why these tests exist at all. A review in The Lancet describes iron deficiency as one of the leading contributors to the global burden of disease, and notes that it particularly affects children and premenopausal women. It also explains that problems can appear before anaemia does (Pasricha et al., 2021).
The four tests in the BPR catalogue
Full Blood Count
The Full Blood Count looks at the main components of the blood: red cells, white cells and platelets. The LML lists 15 markers, including haemoglobin, haematocrit, red cell indices and a five part white cell differential. It gives a general picture of blood health and is the test the NHS describes as the usual first step when anaemia is being considered.
Ferritin
Ferritin is a protein that stores iron. A low ferritin means the body's iron reserves are low, even if haemoglobin is still in range. The LML also notes that ferritin rises with inflammation, which is one more reason to read it alongside other results rather than on its own.
Vitamin D
Vitamin D helps regulate calcium and phosphate, which are needed for healthy bones, teeth and muscles. The NHS explains that we do not make enough vitamin D from sunlight between October and early March, and advises a daily supplement all year for children aged 1 to 4. The marker the LML measures is 25-OH vitamin D.
Anaemia Profile
The Anaemia Profile combines a full blood count with iron studies, vitamin B12 and folate: 17 markers in the LML list. It is useful when the question is not only whether red cells are low but why. The NHS notes that a lack of vitamin B12 can happen with a vegan diet when supplements or fortified foods are not used.
When a blood test tends to make sense
For healthy children, there is no routine schedule of blood tests. The general guidance for this age group is to test only when there is a reason, and to agree that reason with a professional first. Situations that commonly lead to the conversation include:
- tiredness and lack of energy that do not settle, or skin that looks paler than usual, which the NHS lists among the symptoms of iron deficiency anaemia;
- a vegetarian, vegan or otherwise restricted diet;
- a question about vitamin D, especially after winter or in children who spend little time outdoors;
- following up a result that was already outside the expected range.
Many of these signs have ordinary explanations such as sleep, a growth spurt or a busy term. A blood test is one piece of information, not a verdict, and the decision to do one is best made with your GP or the professional who knows your child.
Preparing your child
The NHS describes a blood test as a short procedure: a small amount of blood is usually taken from the inside of the elbow, with a brief scratch as the needle goes in, and any bruising should fade after a few days. A few things help children:
- tell them what will happen in plain words, without promising it will not hurt at all;
- let the person taking the sample know if your child is worried about needles, as the NHS suggests;
- bring a book, a game or a favourite toy for the wait;
- plan something pleasant for afterwards.
