Abstract: TH-PO1109

Workup of Unexplained Renal Hypophosphatemia

Session Information

Category: Fluid, Electrolytes, and Acid-Base

  • 704 Fluid, Electrolyte, Acid-Base Disorders

Authors

  • Bech, Anneke, Radboud University Nijmegen Medical Center, Nijmegen, Nijmegen, Gelderland, Netherlands
  • Hoorn, Ewout J., Erasmus Medical Center, Rotterdam, Netherlands
  • Zietse, Robert, Erasmus Medical Center, Rotterdam, Netherlands
  • Wetzels, Jack F., Radboud University Medical Center, Nijmegen, Netherlands
  • Nijenhuis, Tom, Radboud university medical center, Lent, Gelderland, Netherlands
Background

Hypophosphatemia can be caused by renal phosphate loss. Increased renal phosphate loss can be inherited or acquired. The most common causes of acquired renal hypophosphatemia are medication, Fanconi syndrome, hyperparathyroidism and tumor induced osteomalacia (TIO). The clinical picture of these disorders varies widely and is non-specific. An increasing number of patients with unexplained renal hypophosphatemia is being referred to our clinics.

Methods

We retrospectively evaluated all patients who were referred in the period of 2013-2017 because of unexplained renal hypophosphatemia in two university hospitals in the Netherlands (N=13).

Results

The median age was 51 years and ten patients were male. They did not show any other signs of tubulopathy and did not use drugs known to be associated with hypophosphatemia. Baseline characteristic are shown in table 1.
We performed an 111Indium-pentetreotide SPECT/CT in 5 patients and a 68Ga-DOTA-TOC PET/CT scan in 3 patients. One of these scans showed an increased uptake suggestive of TIO. Genetic testing, performed in all patients, did not show a mutation in genes that are known to be associated with renal phosphate wasting (DMP1, FGF23, FGFR1, GALNT3, PHEX, SLC34A1, SLC34A3, SLC9A3R1).

Conclusion

We have evaluated a group of patients with unexplained renal hypophosphatemuia. Despite extensive and expensive additional investigations, the cause of renal phosphate loss remained unexplained in the majority of patients. The pretest probability of finding a phosphaturic hormone producing tumor on a scan with radiolabeled somatostatin analogs or to find a mutation with genetic analysis in a patient with aspecific complaints and an (inappropriately) normal FGF23 level is low. We therefore advise not to perform scans and genetic analyses as a standard workup in these patients.

Table 1 Baseline characteristics
 MedianRangeReference value
Serum phosphate (mmol/l)0.610.36-0.770.80-1.40
TmP/GFR (mmol/l)0.500.38-0.550.80-1.40
Serum creatinine (µmol/l)8153-14260-110
PTH (pmol/l)5.23.2-8.71.0-6.5
25OHD (nmol/l)7140-135>50
cFGF23 (RU/ml)9253-202<125