Could Alerting Physicians for Low Alkaline Phosphatase Levels Be Helpful in Early Diagnosis of Hypophosphatasia?

OBJECTIVE: Hypophosphatasia (HPP) is an inborn error of metabolism with significant morbidity and mortality. Its presentation is nonspecific leading to delayed or missed diagnosis. Low alkaline phosphatase (ALP) is a diagnostic test. Unlike high ALP, low level is commonly not flagged by laboratories as abnormal. A new treatment was shown to be effective in HPP. In this study we aimed to establish the frequency of low ALP levels requiring notification to physicians by the laboratory and also to describe the clinical manifestations of patients presenting with low ALP for a possible diagnosis of HPP.

METHODS: Patients under age 18 years with low ALP levels were identified from biochemistry records over a period of 6 months. Reference ranges were used as per the Associated Regional and University Pathologists Reference Laboratory (Utah, USA). Electronic results for patients with low levels were checked for flagging as abnormal/low ALP results. Charts of identified patients were reviewed. Presenting features were categorized under groups of disorders.

RESULTS: ALP levels were tested in 2890 patients. 702 had values less than 160 U/L. Of these patients, 226 (32%) had age/gender specific low ALP. None of the low ALP results was flagged as low. Twenty-one had more than one low reading and their charts were reviewed. Four patients in the neuromuscular and four in the miscellaneous group presented with features consistent with HPP despite these patients having no specific diagnoses.

CONCLUSION: Laboratories do not alert physicians in cases with low ALP levels. A persistently low level in patients with unspecified diagnoses could be a key to diagnose HPP. Implementing lab-specific ranges and alerting for low levels could prompt physicians to investigate for undiagnosed HPP.