Predictors of Positive Immunofixation Testing in Patients With Acute Kidney Injury

Abstract Introduction Acute kidney injury may be the presenting manifestation of multiple myeloma, although optimal use of immunofixation testing in this setting is incompletely defined. The authors attempted to determine clinical and laboratory predictors of positive immunofixation testing in patients with acute kidney injury. Patients and Methods The authors did a retrospective study of hospitalized patients with acute kidney injury who had immunofixation studies done. Various clinical and laboratory variables that may be predictive of the presence of multiple myeloma were evaluated and correlations with immunofixation test results determined. Results One hundred twenty-eight patients were studied. Thirteen had a monoclonal paraprotein detected by immunofixation testing (positive result). Patients with positive testing had higher total, ionized and corrected calcium levels, although the median total calcium in immunofixation-positive patients was normal at 9.7 mg/dL. Patients with positive testing also had lower hemoglobin and platelet counts. An anion gap of < 7 mmol/L and total protein-albumin gap > 4 g/dL were also associated with positive results. Conclusions In patients with acute kidney injury, relatively higher total, ionized and corrected calcium levels and lower hemoglobin and platelet counts may predict the presence of a monoclonal paraprotein. An anion gap of < 7 mmol/L and total protein-albumin gap > 4 g/dL may also be predictors. The metabolic consequences of acute kidney injury may attenuate some of these abnormalities as well. These findings may help guide optimal use of immunofixation testing and hence help potentially identify patients who may have multiple myeloma.