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Differential Diagnosis in Adults with Low ALP
Differential Diagnosis in Adults with Low ALP
Differential Diagnosis in Adults with Low ALP
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Video Summary
The webinar reviews how to evaluate persistently low serum alkaline phosphatase (ALP) in adults, emphasizing hypophosphatasia (HPP) as an often-missed genetic cause. Dr. Alia Khan explains that tissue-nonspecific ALP (encoded by the ALPL gene) normally dephosphorylates inorganic pyrophosphate, pyridoxal-5′-phosphate (vitamin B6/PLP), and phosphoethanolamine; when ALP activity is low, these substrates accumulate, impairing bone and tooth mineralization and contributing to neurologic and pain symptoms. Practical points include avoiding EDTA/oxalate tubes (can falsely lower ALP) and interpreting ALP by age/sex, noting transient “pseudonormalization” in pregnancy or after fractures. Common acquired causes to exclude include antiresorptives, severe illness/ICU, malnutrition/malabsorption (e.g., celiac), vitamin/mineral deficiencies (zinc, magnesium, vitamin C), endocrine disorders (hypothyroidism, hypoparathyroidism), renal adynamic bone disease, chemotherapy, and others. If low ALP persists, measure PLP (B6) as an accessible substrate marker; imaging may include skeletal survey (pseudofractures, chondrocalcinosis) and renal ultrasound (nephrocalcinosis). New proposed adult diagnostic criteria require low ALP plus either two major criteria (elevated substrates, ALPL variant, atypical femoral fracture, recurrent metatarsal fractures) or one major plus two minor (poor healing, pain, early tooth loss, nephrocalcinosis, chondrocalcinosis). Management discussion highlights avoiding mislabeling as osteoporosis and caution with antiresorptives; enzyme replacement (asfotase alfa) is preferred when indicated, with limited evidence for anabolic therapies.
Keywords
persistently low alkaline phosphatase
adult hypophosphatasia
ALPL gene mutation
tissue-nonspecific alkaline phosphatase
pyridoxal-5'-phosphate (vitamin B6) elevation
inorganic pyrophosphate accumulation
diagnostic criteria for hypophosphatasia
avoid antiresorptive therapy
asfotase alfa enzyme replacement
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