Blood tests let doctors know what’s going on within your child’s body. Whether it is to address general health or to prevent serious diseases, important blood tests for kids are essential diagnostic tools. Though kids have robust immune systems, they’re still prone to a host of infections and disorders. Sometimes blood tests are also useful in detecting congenital and hereditary disorders. It is important to understand important blood tests for kids to provide effective care for your child. Though routine screenings are avoided in growing kids, there are certain situations when a pediatrician might order a few tests. 

When Is A Blood Test Necessary for Kids?

Your child’s pediatrician orders tests to look for signs that point toward underlying problems. A lot of symptoms are caused by signs that aren’t easily detected on a general physical examination. Important blood tests for kids help the doctor take a closer look and detect problems early. Here are common reasons the tests are ordered:

• To look for abnormalities in the numbers of red and white blood cells & platelets. 
• To look for bodily chemicals that trigger allergies 
• To detect your child’s blood group for future medical records
• Measuring your child’s blood sugar in case your family has a history of diabetes, or to monitor type-1 diabetes that occurs in children. 
• Measuring the levels of excretory products like urea to make sure your kid’s kidneys are functioning properly. 
• Estimating the amount of electrolytes and enzymes to ensure the child’s liver is working effectively. 
• Estimating the kid’s acid-base balance and measuring the saturation of oxygen, carbon dioxide, and nitrogen in the blood. 
• Screening for active infections

Important Blood Tests for Kids & Their Lab Values

Here are some of the most important blood tests for kids recommended by pediatricians. We also provide important lab values for these tests for your reference. Read on to learn more. 

Complete Blood Cell Count

Complete blood cell counts monitor parameters like the number of red blood cells, white blood cells, platelets, and the ratio of blood cells to plasma (hematocrit). These tests are quite routine and are also some of the most important blood tests for kids. Complete blood counts are essential in confirming certain diagnoses, screening for underlying diseases, and also detecting hereditary diseases. The important lab values for complete blood counts are: 

•  Red Blood Cells

Newborns: 4.2 to 5.5 million cells/mcL

6 months - 2 years: 4.1 to 5 million cells/mcL 

2 years - 12 years: 4 to 4.9 million cells/mcL

12 - 18 years: 4.2 to 5.3 million cells/mcL

•  White Blood Cells

Newborns: 6800 to 13300 cells/mcL

6 months - 2 years: 6200 to 14000 cells/mcL

2 years - 12 years: 5300 to 11200 cells/mcL

12 - 18 years: 4500 to 10000 cells/mcL 

• Platelets

Newborns: 164,000 to 351,000 cells/ mcL

6 months - 2 years: 219,000 to 365,000 cells/ mcL

2 years - 12 years: 204,000 to 369,000 cells/ mcL

12 - 18 years: 165,000 to 335,000 cells/ mcL

• Hematocrit 

Newborns: 43.4% to 56.1% 

6 months - 2 years: 30.9% to 37.2% 

2 years - 12 years: 31.7% to 39.6%

12 - 18 years: 34.0% to 43.2%

Blood Grouping Test

Everyone’s blood cells have specific markers on their surfaces called antigens. These antigens are categorized into four different types under the ABO system of blood grouping. The different antigens are A, B, AB, and O. Based on these antigens, there are four blood groups found in all human beings. Another important antigen that helps categorize blood groups is the Rh antigen. A child is either Rh positive or Rh negative depending on the presence of it. Nearly 80% of the population is Rh-positive, while the remainder lacks the antigen. Blood grouping is one of the most important blood tests for kids and helps with: 

• Future medical records.
• Tracing potential blood-relatives. 
• In cases of blood transfusion. 
• Maintaining the safety of both the mother and child in case of an Rh antigen mismatch. 

Blood Sugar Tests

Blood glucose levels are important markers for diabetes and an important blood test for kids and adults alike. Most children afflicted with the condition suffer from type- 1 diabetes. The condition is caused by the destruction of the insulin-producing alpha cells in the pancreas by the immune system. Though it is not completely understood why this happens, a hereditary and genetic component is thought to be responsible. The lack of insulin causes more glucose to be present in the blood, instead of being pulled into the cells to be used as energy. This causes long-term complications and is mitigated by injecting insulin periodically. 

More recently, several children are also being diagnosed with type- 2 diabetes. The condition is usually seen in obese, unhealthy, and middle-aged adults due to a phenomenon called insulin resistance. Something that occurs due to the cells becoming resistant to insulin, an insufficient quantity of insulin being produced, and due to environmental reasons. This increase in early-onset type- 2 diabetes is thought to be due to unhealthy lifestyles, bad habits, and decreased physical activity. Your child’s pediatrician might order blood sugar tests for your child in case they suspect diabetes. The important lab values for this test are: 

• Premature infants: 20 - 80 mg/dL
• Full-term infants: 30 - 100 mg/dL
• Fasting blood glucose in children: <100 mg/dL 
• Post meals: <180 mg/dL

Blood Tests for Allergies 

Though skin testing is the preferred form of testing for allergies, blood tests are employed in the case of infants and young children. Allergy testing with blood samples also happens to be one of the most important blood tests in case the pediatrician suspects serious allergic reactions. Blood tests for allergies revolve around two major components:

• Detecting allergy-causing chemicals in the blood, called antibodies. The antibody called Immunoglobulin E or IgE is linked to allergic reactions. 
• Detecting an increase in specific white blood cells that cause allergies, like eosinophils. 

Commonly performed blood tests for detecting allergies in children are: 

• Enzyme-linked immunosorbent assay (ELISA): Detects IgE and other allergy-causing antibodies in the child’s blood.
• Radioallergosorbent assay (RAST): This test also detects allergy-causing antibodies in the blood. However, the usage of the test has decreased with the introduction of ELISA.
• Total Leukocyte Count (TLC): This test detects the number of white blood cells in the blood. The test also elaborates upon the specific numbers of different white blood cells, giving the doctor an idea about the nature of the allergy. 

Metabolic Panel

This test gives your child’s pediatrician a complete idea about how your child’s body is functioning on the subtlest levels. The test looks for specific chemicals, enzymes, and electrolytes that determine smooth functioning. Metabolic panels are some of the most important blood tests for kids as they are direct markers of liver & kidney function. The tests also provide insight into the body’s acid-base balance and blood buffer systems that maintain essential salts at optimal levels. Here are the important lab values for this test: 

• Sodium: 136 - 144 mEq/ L
• Potassium: 3.7 - 5.2 mEq/ L
• Chloride: 96 - 106 mmol/ L
• Calcium: 8.5 - 10.2 mg/  dL
• Blood Glucose: <100 mg/dL (fasting)
• Carbon Dioxide: 23 - 29 mmol/ L
• Blood Urea Nitrogen: 6 - 20 mg/dL
• Creatinine: 0.8 - 1.2 mg/dL
• Alkaline Phosphatase (ALP): 44 - 147 IU/ L
• Alanine Aminotransferase (ALT): 7 - 40 IU/ L
• Aspartate Aminotransferase (AST): 10 - 34 IU/ L
• Bilirubin: 0.3 - 1.9 mg/dL
• Albumin: 3.5 - 5.4 g/ dL
• Total Protein: 6 - 8.3 g/ dL

If the test shows skewed or varying values, your child’s doctor may order further tests to detect the underlying condition.

Pediatric Lipid Profile

Until recently, lipid testing was deemed unnecessary in children. However, with an increase in unhealthy lifestyles, obesity, and high sugar diets, even children are now deemed to be at risk of high cholesterol. Cholesterols are commonly called fats and are found in the body and perform several functions. However, certain types of it can increase the risk of heart disease and complicate normal life. A lipid profile measures the amount of high-density lipoprotein (good cholesterol), low-density lipoprotein (bad cholesterol), total cholesterol, and triglycerides (freely present fats) in the blood. These tests help doctors determine potential risks from cholesterol to your child’s health. The test is usually avoided in children below the age of two and pubescent teenagers due to fluctuating lipid levels. Children in the other age groups are fit for testing. Here are the test’s normal values:

• Total Cholesterol: <170 mg/dL
• LDL Cholesterol: <110 mg/dL
• HDL Cholesterol: 45 mg/dL or higher 
• Triglycerides: <100 mg/dL

Hemoglobin Test

Hemoglobin is a protein present on the red blood cells’ surface that carries oxygen to different parts of the body. The protein contains iron, and the metal is essential to this protein’s production in the body. Testing for hemoglobin levels is an important blood test for kids as it lets doctors know if your child has iron-deficiency anemia. In case your child suffers from chronic weakness, has pale fingernails, or a pale discoloration of the skin, the doctor might recommend this test. A hemoglobin test along with hematocrit levels from complete blood count help the pediatrician assess the iron levels in your child’s body. Important lab values for this test are- 

• 0.5 to 5 years: 11 g/ dL or higher 
• 6 to 12 years: 11.5 g/ dL or higher
• 12 to 18 years: 12 g/ dL or higher

Screening for Heavy Metal Poisoning

Metals like lead and cadmium were once used in pigments incorporated in paint and other objects like crayons. The use of these metals in pigments was banned after the 70s, however, certain children still tend to be susceptible due to the environment they live in. In case you live in an area that is prone to pollution by heavy metals or live in a house that was constructed and embellished a long time ago, your doctor may recommend this test. Irrespective of the risk, this test is an extremely important blood test for kids as heavy metal poisoning can cause serious issues like stunting, growth defects, and can even be life-threatening.

The test involves collecting the blood sample and making it react with a specific chemical that binds to heavy metals. If the sample is found to react with the chemical reagent, then heavy metal poisoning is detected. Further, tests like urine examinations can be ordered in case your child’s doctor wants a closer assessment of the situation.

Tuberculosis Screening

The tuberculosis screening tests are important blood tests for kids that might have compromised immune systems or for those who have come in contact with an infected individual. Tuberculosis blood tests are usually ordered following the skin tests, but sometimes pediatricians order just the blood tests. TB blood tests just let you know whether your child has been infected with TB bacteria, and not if the disease is active.

Further testing following the TB blood tests is required to tell if your child has an active tuberculosis infection. The TB blood test is called the Interferon Gamma Release Assay or IGRA. The test involves detecting the body’s production of interferon-gamma, an important chemical released by the immune system to counter the tuberculosis bacteria. There are various options available for testing and a robust treatment methodology exists to treat tuberculosis once detected. 

HIV & Other Sexually Transmitted Diseases

HIV is a virus that can be passed onto children from an infected mother through the placenta. The same mode of transmission applies to a host of other sexually transmitted diseases such as syphilis, chlamydia, hepatitis B, gonorrhea, HPV, and herpes. Children show specific signs that hint toward placental or sexually transmitted diseases. This might cause your doctor to order tests to detect these diseases to enable timely treatment of the condition. Though it might seem odd to some, testing for STDs and HIV are some of the most important blood tests for kids to provide them comprehensive medical care. 

The procedure for these important blood tests for kids involves either single or multiple blood draws depending on the requirement and the condition. Most pediatricians recommend these tests only after complete physical examinations and other preliminary tests. Most of these tests yield results within 24 hours, however, some specific tests might take longer. These tests are important to children's’ health and are the driving force in detecting preventable conditions before they cause serious consequences.