Transient Hyperphosphatasemia Following Pediatric Kidney Transplant.

Introduction Transient hyperphosphatasemia (TH) is a rare benign condition of elevated serum alkaline phosphatase (AP) levels seen in healthy children. TH has been reported to occur in pediatric solid organ transplants, including kidney transplant patients. Little is known about TH in pediatric kidney transplant patients. Objective To evaluate the incidence and natural history of TH in pediatric kidney transplant patients. Methods A retrospective chart review of patients < 18 years of age who underwent kidney transplantation at the University of Pittsburgh Medical Center (UPMC) Children's Hospital of Pittsburgh between 2008 and 2019 was performed to identify patients with TH, defined as an AP level greater than 1,000 IU/L. Exclusion criteria included repeat kidney transplants or kidney transplant as part of a multiorgan transplant. Results One hundred seventy-six patients underwent a solitary kidney transplant, of which 87 were less than 12 years of age. Eleven patients (6.5%) were found to have TH, all of whom were < 12 years of age (12.8%) (median age: 5 years; range: 1 - 11 years). The median AP level prior to transplant was 183 IU/L (range: 104 - 309 IU/L) and the median peak AP was > 2,300 IU/L (range: 1,227 - 4,912 IU/L). The median time from a kidney transplant to the diagnosis of TH was 0.6 years (range: 0.3 to 7.7 years). The median length of time that TH persisted was 0.5 years (range: 0.2 to 0.9 years). The median estimated glomerular filtration rate (GFR) at the time of diagnosis of TH was 84 mL/min/1.73m per the bedside Schwartz equation (range: 45 to 152 mL/min/1.73m). One patient had variable AP levels over nine months prior to resolution; the other 10 patients had a solitary peak of AP prior to resolution. No patient required treatment of elevated AP levels and the TH resolved spontaneously without intervention. No patients had significant abnormalities of markers of metabolic bone disease or were on active vitamin D, calcium, or phosphorus supplements. Two patients reported bone pain, and one patient was found to have avascular necrosis of the hip. Conclusions TH is a relatively common finding following a pediatric kidney transplant in pre-pubertal children less than 12 years of age. It primarily occurs in the first year following a kidney transplant and usually resolves without recurrence within one year of onset.