What is the normal bilirubin level in a 16-year-old female?

Normal Bilirubin Levels in a 16-Year-Old Female

The normal total bilirubin level for a 16-year-old female is less than 1.2 mg/dL (20.5 μmol/L), with direct (conjugated) bilirubin typically comprising less than 20-30% of the total value.

Normal Reference Ranges

• For females aged 15-19 years, the normal hemoglobin range is 121.6-144.2 g/L (12.1-14.4 g/dL), which indirectly relates to bilirubin production as bilirubin is a byproduct of hemoglobin breakdown 1
• Total bilirubin in healthy adolescent females should typically be below 1.2 mg/dL, with values above this threshold considered elevated 1, 2
• Direct (conjugated) bilirubin should normally be less than 0.3 mg/dL or less than 20-30% of the total bilirubin value 1, 2

Interpretation of Bilirubin Values

• Bilirubin exists in two forms: unconjugated (indirect) and conjugated (direct), with the latter being water-soluble and created in the liver for excretion 1
• Total bilirubin represents the sum of both unconjugated and conjugated fractions 1
• In adolescents and adults (unlike neonates), the majority of measurable bilirubin should be conjugated 1

Clinical Significance of Bilirubin Levels

Normal Range Significance

• Bilirubin within normal range indicates proper liver function and normal red blood cell turnover 2
• Mild elevations (1.2-2.0 mg/dL) may be seen in Gilbert's syndrome, which affects 5-10% of the population and is characterized by intermittent unconjugated hyperbilirubinemia without evidence of liver disease 2

Abnormal Values

• Total bilirubin >1.2 mg/dL may indicate:
  • Gilbert's syndrome (benign condition) if predominantly unconjugated 2
  • Early liver disease if predominantly conjugated 2
  • Hemolysis (increased red blood cell breakdown) 1
• If direct bilirubin exceeds 35% of total bilirubin, this suggests hepatobiliary disease 2

Factors Affecting Bilirubin Levels

• Fasting can temporarily increase unconjugated bilirubin levels, particularly in individuals with Gilbert's syndrome 2
• Certain medications can affect bilirubin metabolism 1
• Stress and illness may cause transient elevations in bilirubin 2

Important Considerations for Measurement

• Bilirubin is photosensitive but stable in plasma samples for up to 8 hours when exposed to normal laboratory lighting at room temperature 3
• For accurate results, blood samples should be protected from light if analysis will be delayed more than 8 hours 3
• Samples can be stored at refrigerator temperature (3°C) or room temperature (22°C) with light protection for at least 24 hours without significant changes in bilirubin concentration 3

Clinical Pearls

• Even mild hyperbilirubinemia should not be ignored as it can be an early indicator of significant liver disease 2
• Low bilirubin levels (<0.5 mg/dL) have been associated with increased oxidative stress and potentially higher risk of coronary artery disease in some studies 4, 5
• When evaluating elevated bilirubin, it's essential to assess other liver function tests (AST, ALT, ALP, GGT) to determine the pattern of liver injury 2

Remember that bilirubin values should always be interpreted in the context of other laboratory findings and the patient's clinical presentation.