Un co rre cte d

Objectives: Hypophosphatasia (HPP) is an inborn error of metabolism with significant morbidity and mortality. Its presentation is non-specific leading to delay or missed diagnosis. Low ALP is a diagnostic test. Unlike high ALP, low level is commonly un-flagged by laboratories as abnormal. A new treatment has proved to be effective in HPP. We aim to study frequency of flagging of low ALP level by laboratory and the clinical manifestations of patients presenting with low ALP for a possible diagnosis of HPP. Methods: Patients under 18 with low ALP were identified from biochemistry records over a period of 6 months. Reference ranges were used as per the ARUP directory. Electronic results for patients with low level were checked for flagging as abnormal/low ALP results. Charts of identified patients were reviewed. Presenting features were categorized under groups of disorders. Results: 2890 patients had ALP test. 702 had values less than 160 U/L. 226 had age/gender specific low ALP. None of the low ALP results was flagged as low. 205 patients were excluded. Charts of 21 patients were studied further. 4 patients under the neuromuscular and 4 in the miscellaneous group presented with features suspected of HPP and had no specific diagnoses. Such patients could be potentially HPP patients. Conclusion: Low levels of ALP are not alerted for by lab. 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 be a way to detect undiagnosed HPP. Un co rre cte d What is already known on this topic: • Hypophosphatasia is a rare disorder with significant morbidity and mortality • High level of Alkaline Phosphatase is commonly alerted for by biochemistry labs • Asfotase alpha is a new and effective medication for hypophosphatasia treatment What this study adds: • Unlike high alkaline phosphatase, low alkaline phosphatase is not always alerted for by biochemistry labs • Identification of children presenting with unspecific clinical features and have more than one reading of low alkaline phosphatase could help diagnosing children with hypophosphatasia. • Devising lab specific reference ranges for alkaline phosphatase is important to avoid missing of abnormally low levels.