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Background
Benign transient hyperphosphatasia (BTH) is a disorder characterised by transient marked increases in alkaline phosphatase (ALP) activity in the absence of bone or liver disease. It was first reported by Bach in 1954 as a condition occurring in infancy and early childhood only.
The aetiology of BTH remains unclear. However, a number of theories have been put forward to explain the transient rise in ALP activity. Firstly, increased hepatic ALP synthesis as part of the acute phase reaction 1 - 3 was postulated, as infectious diseases have accompanied some cases of BTH. 4 - 6 However, BTH has also been observed in healthy subjects and during the course of a wide variety of clinical disorders. 2 , 4 Secondly, decreased clearance of ALP from circulation due to increased sialation of the enzyme is the most probable mechanism, although the cause of the altered sialation in BTH remains uncertain. This possibility is supported by the abnormal sialation of liver and bone isoenzyme fractions reported by Crofton. 7
The prevalence of BTH in infants is unknown. In 1966, Asanti et al studied ALP in 260 healthy infants and 1.5% had an unexplained transient rise in ALP activity to more than 3 times the upper reference limit (URL) for the assay. In the acute medical setting, Parker studied a population of 204 adults and found that 32% of the cases of hyperphosphatasia were attributed to BTH. However in these cases the elevation in ALP was less than three times the upper reference limit. 8 In 2001 this prevalence was supported by a similar finding in acutely ill children. 9 This transient raised ALP is often found incidentally during routine biochemical investigations. The aim of this case report is to present two new cases of BTH in adults and to suggest criteria for the diagnosis of this condition at an early stage to avoid performing expensive and possibly invasive tests.
Case presentation
Case 1
A 59-year-old woman attended her general practitioner (GP) surgery for a routine check-up. She was found to have grossly elevated serum ALP activity at 5206 IU/litre (relative risk (RR): 70-300 IU/litre) but other liver function tests (bilirubin, alanine transaminase, [GAMMA]-glutamyltransferase) were within reference limits. This result was confirmed 2 days later (6003 IU/litre). Subsequent...