Differential Diagnosis in Adults with Low ALP-Differential Diagnosis in Adults with Low ALP

Video Transcription

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.

Meta Tag

Concept Alkaline Phosphatase

Concept Alkaline Phosphatase Deficiency

Concept Hypophosphatasia

Concept Pyridoxal Phosphate

Concept Phosphoethanolamine

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

Alkaline Phosphatase

Alkaline Phosphatase Deficiency

Hypophosphatasia

Pyridoxal Phosphate

Phosphoethanolamine


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