Low alkaline phosphatase (ALP) levels characterize a rare genetic disease, hypophosphatasia. Hypophosphatasia is a phenotypically heterogeneic disease, and clinical severity may range from asymptomatic to severely disabling. Importantly, hypophosphatasia can be mistaken for osteoporosis, which is commonly treated with bisphosphonate therapy. If bisphosphonates are given to a patient with hypophosphatasia, this may worsen the bone disease. In many such cases a low ALP level may be the only clue to the existence of this disease. Diagnosis of hypophosphatasia involves clinical features, biochemical features (low serum ALP and elevated substrates of the tissue nonspecific ALP enzyme) and radiological features. There are no guidelines regarding the diagnosis or further investigation of this disorder.
Patients with persistently low ALP levels may have undiagnosed hypophosphatasia, and we hypothesize that although rare, hypophosphatasia may be more common than is currently recognized. To date, there are few studies evaluating this.
The aim of our retrospective consecutive electronic and paper chart audit was to determine whether consistently significantly low ALP levels are associated with an increased risk of bone disease (particularly bone pain, recurrent fractures and osteoporosis or osteopenia) and to evaluate for correlations with age, sex, comorbidities and medications.
We have collected data from all patients in a tertiary rural referral hospital with persistently low ALP levels over a one year period. Subjects were identified by searching the Queensland Health Pathology and Scientific Services Laboratory Information System for all patients with consistently (greater than one) low ALP activity. We have collected data regarding medication usage, particularly bisphosphonate use, history of fractures or osteoporosis, family history of fractures or osteoporosis, skeletal imaging and patient demographics. This will expand clinical knowledge regarding the clinical relevance of low ALP levels. Preliminary analysis indicates that 9.48% of the subjects have osteoporosis, further analysis is pending.