Hyperphosphatemia By James L Lewis III, MD, Brookwood Baptist Health and Saint Vincent's Ascension Health, Birmingham Reviewed / Revised Sep 2021 | Modified Sep 2022 View Patient Education Etiology Pathophysiology Symptoms and Signs Diagnosis Treatment Key Points Hyperphosphatemia is a serum phosphate concentration > 4.5 mg / dL (> 1.46 mmol/L).