Is an Alkaline Phosphatase of 83 U/L Concerning in a 16-Year-Old?
An ALP of 83 U/L in a 16-year-old is not concerning and is actually below the expected physiologic range for this age, as adolescents normally have ALP levels 2–3 times higher than adults due to active skeletal growth. 1
Understanding Normal ALP in Adolescence
Adolescents have physiologically elevated ALP levels compared to adults because bone-specific ALP represents 80–90% of total circulating ALP during periods of active skeletal development. 1, 2
Peak ALP levels occur during puberty, with boys typically showing higher values at ages 12–17 years and girls at ages 10–12 years, after which levels gradually decline toward adult ranges. 3
A level of 83 U/L is well below the typical adolescent range, which can extend to several hundred U/L depending on pubertal stage and sex. 3, 4
When Low ALP Would Be Concerning
Persistently low ALP (<100 U/L on repeated testing) in children and adolescents may indicate hypophosphatasia, a rare genetic disorder of bone mineralization caused by mutations in the ALPL gene. 5
If this 16-year-old has a history of recurrent fractures, dental problems (premature loss of primary teeth), bone pain, or short stature, then further evaluation with repeat ALP, plasma pyridoxal-5'-phosphate, and urinary phosphoethanolamine would be warranted. 5
In the absence of clinical symptoms or bone disease, a single low-normal ALP measurement requires no immediate action beyond consideration of repeat testing in 3–6 months if clinical suspicion exists. 5
Practical Interpretation
Most adolescents with ALP in the 80s U/L range are either post-pubertal (growth plates closing) or have completed their growth spurt, which is a normal physiologic finding. 3
No further workup is needed unless there are accompanying symptoms such as fractures, bone deformities, dental abnormalities, or a family history of bone disease. 5
Transient variations in ALP are common and a single value should not prompt extensive investigation in an otherwise healthy teenager. 6, 4