Is an alkaline phosphatase (ALP) level of 85 significant in a 14-year-old and what are the next steps?

Significance of Alkaline Phosphatase Level of 85 in a 14-Year-Old

An alkaline phosphatase (ALP) level of 85 in a 14-year-old is within normal range and not clinically significant, requiring no further workup in the absence of other concerning symptoms or laboratory abnormalities. 1

Understanding ALP in Adolescents

• In children and adolescents, 80-90% of total ALP originates from bone tissue, compared to only about 50% in adults 1
• ALP levels naturally fluctuate during periods of bone growth, with higher levels expected during puberty due to increased osteoblastic activity 1
• Normal ALP reference ranges are age-dependent and typically higher in adolescents than adults due to active bone growth 2

Clinical Context for ALP Interpretation

• Elevated ALP (above age-specific reference range) is a biochemical hallmark of conditions like X-linked hypophosphatemia (XLH), where it would be accompanied by hypophosphatemia and renal phosphate wasting 2
• In children with active rickets or osteomalacia, ALP levels would be significantly elevated above the age-appropriate reference range 2
• When evaluating ALP levels, they should be interpreted alongside other laboratory parameters including:
  • Serum phosphate levels 2
  • Calcium levels 2
  • Parathyroid hormone (PTH) levels 2
  • Vitamin D status 2

When Further Evaluation Is Warranted

ALP levels would warrant further investigation in the following scenarios:

• Values significantly above age-specific reference ranges 2
• Persistent elevation on repeated measurements 3
• Presence of clinical symptoms suggesting:
  • Bone disease (rickets, growth abnormalities, bone pain) 2
  • Liver disease (jaundice, hepatomegaly) 1
  • Other systemic conditions 4

Potential Causes of Truly Elevated ALP in Adolescents

If ALP were actually elevated (which it is not in this case), potential causes would include:

• Physiologic elevation during growth spurts 1
• Bone disorders:
  • Rickets/osteomalacia 2
  • Healing fractures 1
• Liver disorders:
  • Cholestatic liver disease 1
  • Infiltrative liver disease 5
• Transient hyperphosphatasemia - a benign condition in children that resolves spontaneously 3

Conclusion

The ALP value of 85 in a 14-year-old is within normal limits and does not require additional investigation in the absence of other clinical or laboratory abnormalities. Normal ALP levels in adolescents are typically higher than in adults due to active bone growth during puberty 1.