Case report Spurious hypophosphatemia associated with monoclonal paraproteinemia

Hypophosphatemia is a relatively uncommon finding in clinical practice, with a prevalence of 1–5% in all hospitalized patients. However, it is an adverse prognostic marker for mortality and morbidity. Although the correlation between serum phosphate levels and symptoms is not linear, severe hypophosphatemia is important to recognize and treat since it can lead to rhabdomyolysis, haemolysis, respiratory failure secondary to diaphragmatic weakness and neurological abnormalities. We report a case of spurious hypophosphatemia in a patient with longstanding MGUS coincident with the onset of Waldenstrom’s macroglobulinemia due to paraprotein interference with the phosphate assay used. Clinicians should be aware of the possibility of spurious phosphate measurements in patients with paraproteinemias to avoid unnecessary investigation and intervention.