Transient, marked, unexplained elevation of serum alkaline phosphatase.

Five children, aged 16 to 38 months, were found to have serum alkaline phosphatase levels seven to 30 times the upper limit of the reference range. Studies suggested a skeletal origin for the enzyme. No other abnormalities or explanations for the unusual enzyme levels were found. The enzyme levels returned to the reference range. A retrospective review of the records of 74 children with lymphoblastic leukemia, who were 2 to 4 years of age at diagnosis, disclosed only four cases of transient, isolated serum alkaline phosphatase elevation similar in degree to those described herein. The review covered 661 patient-years follow-up and 2,417 enzyme measurements. Benign, transient hyperphosphatasemia is a rarely recognized clinical entity. Awareness of this condition should curtail the extensive evaluation that may follow the detection of such an abnormality.