Oral Presentation ANZBMS-MEPSA-ANZORS 2022

A low serum alkaline phosphatase may signal the presence of hypophosphatasia in patients with reduced bone mineral density or fragility fractures (#22)

Elisabeth Ng 1 2 , Claudia Ashkar 2 , Ego Seeman 3 4 , Hans-Gerhard Schneider 2 5 , Hanh Nguyen 1 6 , Peter Ebeling 1 6 , Shoshana Sztal-Mazer 2 7 8
  1. Department of Endocrinology, Monash Health, Clayton, Victoria, Australia
  2. Department of Endocrinology & Diabetes, Alfred Health, Melbourne, Australia
  3. Department of Medicine, The University of Melbourne, Melbourne, Australia
  4. Department of Endocrinology, Austin Health, Melbourne, Australia
  5. Clinical Biochemistry Unit, Alfred Pathology Service, Alfred Health, Melbourne, Australia
  6. Department of Medicine, School of Clinical Sciences, Monash University, Clayton, Australia
  7. School of Public Health, Monash University, Melbourne, Australia
  8. School of Medicine, Monash University, Melbourne, Australia

Introduction 

Hypophosphatasia (HPP) is an inherited disorder associated with impaired primary mineralisation of osteoid (osteomalacia). HPP may be misdiagnosed as osteoporosis, a reduction in the volume of normally mineralized bone. Both illnesses may result in fragility fractures. Antiresorptive therapy, first-line treatment for osteoporosis, is contraindicated in HPP. Misdiagnosis and mistreatment can be avoided by recognising a low serum alkaline phosphatase (ALP).

 

Methods

The prevalence of a low ALP (<30 IU/L) was determined in a study of patients attending an Osteoporosis Clinic at a tertiary hospital during 8 years (2012-2020).  Patients were categorised into those with a low ALP during one month, during at least two months but less than half of all months when ALP was measured, and in over half of all months when ALP was measured. The third group identified a persistently low ALP, minimising inclusion of patients with serial low levels within a brief time period.  

 

Results

Of 1839 patients, 168 (9%) had at least one low ALP, 50 (2.7%) had low ALP during at least two months and seven (0.4%) had low ALP levels for at least half of all months when the ALP was measured. HPP has been diagnosed in four patients, three of whom had persistently low ALP levels. The prevalence of HPP was 0.22% of patients in the Osteoporosis Clinic and 2.38% of patients with at least one low ALP.

 

Conclusion

Persistently low ALP in Osteoporosis Clinic attendees signals the likelihood of a diagnosis of hypophosphatasia, a condition that may be mistaken for osteoporosis and incorrectly treated with antiresorptive therapy.