Fluctuating creatinine in the cardiac unit

Background: Inconsistent serum creatinine results were observed in a patient with a history of λ light-chain (AL) amyloidosis with multiple comorbidities, including renal nephropathy. Throughout admission, serum creatinine concentrations varied and were inconsistent with the patient's clinical presentation. Studies were conducted to elucidate the cause of the observed fluctuations. Methods: Whole blood plasma and serum samples were assessed using alternate methodologies and confirmed a falsely low creatinine concentration when analyzed using an enzymatic methodology. A review of the patient's chart identified a potential interfering substance, which was verified via spiking studies. A review of the specimen collection practices was also conducted to understand the intermittently low creatinine values. Results: Upon admission, the patient's serum creatinine concentration was 1.7mg/dl. However, creatinine values varied from 0.6 to 1.9mg/dl in the proceeding days, and the low creatinine concentrations were inconsistent with the patient's clinical presentation. To investigate, paired specimens were collected for whole blood plasma analysis via amperometric detection and serum analysis using either enzymatic or Jaffe methodologies. Enzymatic measurement of creatinine resulted in a lower creatinine concentration (0.6mg/dl) as compared to kinetic Jaffe or whole blood testing (1.8mg/dl). Following consultation with the clinical team, the patient had been administered dopamine intravenously in the days following admission. Studies illustrated dopamine concentrations above 6.50×10⁵pg/ml resulted in decreased creatinine concentrations when measured enzymatically. The intermittent low creatinine concentrations observed were due to collection via a peripherally inserted central catheter line. Conclusion: Fluctuations in serum creatinine concentrations in a hospitalized patient were due to interference by dopamine. Samples collected from a peripherally inserted central catheter line in which dopamine was administered resulted in the suppression of peroxidase assays that use phenazone as a substrate.