Common Laboratory Diagnostics In Primary Pediatric Care

Common laboratory diagnostics in primary pediatric care settings

Identify and describe the purpose of various pediatric laboratory tests, including their normal ranges, indications for high or low levels, and reasons for ordering each test.

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In primary pediatric care, laboratory testing is an essential component for diagnosing, monitoring, and managing various health conditions. These tests provide valuable information about a child's physiological status, nutritional deficiencies, metabolic functions, and potential exposure to toxins or infectious agents. Understanding the purpose, normal ranges, and clinical indications for each test enables healthcare providers to make informed decisions and provide appropriate interventions.

Basic Metabolic Panel (BMP): BUN and Creatinine Tests

Blood Urea Nitrogen (BUN) and Creatinine are common tests included in the basic metabolic panel, used to evaluate kidney function. The normal BUN range varies by age: infants typically have a range of 5-18 mg/dL, children 5-18 mg/dL, and adolescents 7-20 mg/dL. Elevated BUN levels can indicate renal insufficiency, dehydration, or increased protein catabolism, whereas low levels may suggest liver dysfunction or malnutrition. Similarly, serum creatinine levels are indicative of glomerular filtration rate; normal ranges are approximately 0.2-0.4 mg/dL in infants, 0.3-0.7 mg/dL in children, and 0.6-1.2 mg/dL in adolescents. High creatinine points to impaired kidney function, dehydration, or muscle breakdown, whereas low levels are generally not clinically significant but may reflect decreased muscle mass. These tests are ordered to assess kidney health, monitor renal disease progression, and evaluate hydration status.

Urinalysis

Urinalysis is a non-invasive diagnostic tool used to detect urinary tract infections, kidney disease, and metabolic disorders. The dipstick measures various parameters: pH typically ranges from 4.5 to 8; leukocytes can indicate infection or inflammation; nitrite suggests bacterial presence; protein, glucose, and ketones can point toward metabolic disturbances like diabetes or renal impairment; specific gravity assesses urine concentration; blood may reveal bleeding; and RBCs (red blood cells) and other cells can suggest pathology. High leukocytes or nitrites often indicate urinary tract infection, while elevated protein suggests kidney damage or disease. Low levels of these parameters generally confirm normal urinary function. Urinalysis assists in diagnosing infections, monitoring renal health, and screening for metabolic conditions.

Complete Blood Count (CBC): Hemoglobin, Hematocrit, and Platelets

Hemoglobin (HGB) and Hematocrit (HCT) data are vital for identifying anemia or polycythemia. Normal HGB ranges are approximately 11-13 g/dL in infants, 11.5-15.5 g/dL in children, and 12-16 g/dL in adolescents. Elevated levels may indicate dehydration or polycythemia vera, whereas low levels suggest anemia, which can be caused by nutritional deficiencies, chronic disease, or blood loss. Platelet counts are essential for coagulation assessments; normal values are about 150,000 to 450,000 per microliter across age groups. Thrombocytopenia (low platelets) may lead to bleeding tendencies, and thrombocytosis can be associated with inflammatory states. These CBC components are ordered routinely to evaluate overall health, detect hematologic disorders, and monitor conditions like bleeding or clotting abnormalities.

Reticulocyte Count

The reticulocyte count measures immature red blood cells, providing information about bone marrow activity and RBC production. Normal ranges are approximately 0.5-1.5% of total RBCs. Elevated reticulocyte levels indicate increased erythropoiesis, often in response to anemia or blood loss, whereas low levels suggest marrow suppression or deficiency of erythropoietin. It is ordered to differentiate between types of anemia and assess the marrow’s response to anemia or therapy.

White Blood Cell (WBC) Differential: Neutrophils, Bands, Eosinophils, Lymphocytes, Monocytes, Basophils

For each WBC subtype, normal ranges vary: neutrophils (~40-60%), bands (0-5%), eosinophils (1-4%), lymphocytes (20-40%), monocytes (2-8%), basophils (0.5-1%). Neutrophils help fight bacterial infections; elevated levels suggest bacterial infection or inflammation. Increased bands, known as left shifts, also indicate bacterial infections or immune response. Elevated eosinophils are associated with allergies or parasitic infections. Lymphocytosis can occur in viral infections, while monocytes increase in certain bacterial, viral, or inflammatory conditions. Basophilia may be seen in allergic reactions or hematologic disorders. The differential helps identify specific causes of infection or inflammation and guides targeted treatment.

Hemoglobin A1c

Hemoglobin A1c reflects average blood glucose levels over approximately three months. Normal ranges are below 5.7%. Elevated levels (above 6.5%) suggest diabetes mellitus or poor glycemic control. This test assists in diagnosing, monitoring, and managing diabetes, ensuring effective intervention to prevent complications.

Blood Lead Level

The normal blood lead level for children is generally considered below 5 micrograms per deciliter. Levels above this threshold indicate potential lead poisoning, which can cause neurological and developmental impairments. Elevated blood lead levels warrant environmental evaluation and interventions to eliminate exposure sources.

Sweat Chloride Test

The sweat chloride test is primarily used to diagnose cystic fibrosis. Normal sweat chloride levels are below 30 mmol/L in children; intermediate results range from 30-59 mmol/L, and levels above 60 mmol/L are diagnostic of cystic fibrosis. An abnormal test indicates defective chloride channels, guiding further genetic testing and management.

Electrolytes: Potassium and Sodium

Normal serum potassium ranges from 3.5 to 5.0 mmol/L, and sodium from 135 to 145 mmol/L across pediatric age groups. Elevated potassium can indicate renal failure, dehydration, or cell breakdown; low levels suggest hypokalemia caused by diuretics or vomiting. Sodium disturbances may reflect dehydration, hyponatremia, or other fluid imbalances. These tests are ordered to assess electrolyte balance, monitor kidney function, and evaluate acid-base status.

Fasting Blood Glucose

Normal fasting blood glucose in children is less than 100 mg/dL. Elevated levels indicate impaired glucose regulation, prediabetes, or diabetes mellitus. This test is essential for screening and diagnosis of glucose metabolism disorders.

Thyroid Function Tests: TSH, T3, and Free T4

TSH normal range is approximately 0.5-4.0 mIU/L; T3 levels vary but are typically 80-200 ng/dL, and free T4 ranges from 0.8 to 1.8 ng/dL. Elevated TSH suggests hypothyroidism, while low TSH indicates hyperthyroidism. Abnormal T3 and T4 levels further clarify thyroid status. These tests guide diagnosis and management of thyroid disorders in pediatric patients.

Oxygen Saturation

Normal oxygen saturation levels are between 95-100%. Levels below 90% indicate hypoxemia, requiring intervention. Continuous monitoring helps assess respiratory function, especially in children with respiratory illnesses or cardiac conditions.

Serum pH and Magnesium

Serum pH normal range is 7.35-7.45, reflecting acid-base balance. Abnormal pH indicates acidosis or alkalosis, requiring prompt correction. Serum magnesium levels (1.7-2.2 mg/dL) are important for neuromuscular function; abnormalities can cause neurological or cardiovascular disturbances.

Alanine Aminotransferase (ALT) and Aspartate Aminotransferase (AST)

ALT and AST are enzymes measuring liver health; normal ALT values are 7-56 IU/L, and AST 10-40 IU/L. Elevated levels suggest liver inflammation, injury, or disease. Monitoring these enzymes helps assess hepatic function in children with suspected liver pathology.

Conclusion

Routine pediatric laboratory diagnostics are vital for early detection and management of health issues. Familiarity with the normal ranges, indications of abnormal levels, and reasons for testing ensures that healthcare providers can interpret results accurately and tailor care to pediatric patients' needs. These tests collectively contribute to a comprehensive assessment, promoting better health outcomes in the pediatric population.

References

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  • Levy, J., & Silberstein, J. (2018). Pediatric Nephrology and Renal Laboratory Tests. Pediatric Nephrology, 33(7), 1073–1081.

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