Clinical Contexts of Detection of Benign Transient Hyperphosphatasemia in Infants and Young Children: A Single-Center Retrospective Study

Background: Transient hyperphosphatasemia (TH) is a benign, self-limited condition characterized by a marked but temporary elevation of serum alkaline phosphatase (ALP), typically exceeding 3-5 times the upper limit of the age-adjusted reference range, in otherwise healthy infants and young children. Because extreme ALP elevations may raise concern for liver or bone disease, clarification of its clinical characteristics is important. Methods: We conducted a retrospective single-center study of children diagnosed with TH at a tertiary pediatric center. TH was defined as a marked but temporary elevation of serum ALP in the absence of clinical or laboratory evidence of bone or liver disease, with spontaneous normalization within several months. Demographic characteristics, clinical symptoms, associated infections, and laboratory findings (including ALP isoenzyme levels) were analyzed. Results: Forty-one children were included, with a median age of 13 months (IQR 11-18 months). Associated infections were identified in 29 patients, most commonly viral gastroenteritis and respiratory viral infections, although no single pathogen predominated. In 12 patients, TH was detected incidentally during blood testing performed for unrelated clinical reasons. The median peak ALP level was 2,304 U/L (IQR 1,699-3,985 U/L), with values exceeding 10,000 U/L in some cases. ALP isoenzyme analysis demonstrated elevation of both liver and bone isoenzymes in all patients. Peak ALP levels did not differ between sexes or between patients with and without associated infections. Conclusions: TH predominantly affects infants and toddlers and may be detected both during evaluation of mild infections and incidentally during routine laboratory testing. Recognition of this benign condition is important to prevent unnecessary diagnostic investigations and to reassure caregivers when marked ALP elevation is encountered in otherwise healthy young children.