Dr JESSICA SUN1,2, Dr MARGARET JANU1,2,3, Dr SHAUNDEEP SEN1,2
1Concord Repatriation General Hospital, Concord, Australia, 2University of Sydney, Camperdown, Australia, 3NSW Health Pathology, Sydney, Australia
Background
Serum creatinine (sCr) is the most common marker used to estimate glomerular filtration rate. It is measured by either the colorimetric (Jaffe) method, or newer enzymatic assays. There are well-known interferences with the Jaffe method including glucose, ascorbic acid, bilirubin, and drugs such as cephalosporins. Enzymatic assays are less susceptible to influence by such chromogenic substances, but interference by paraproteins with these newer methods has been infrequently reported. We report a less well-described case of falsely elevated sCr measured by the Jaffe method.
Case report
An 81-year-old male with known IgM monoclonal gammopathy of uncertain significance (kappa light chain overlying beta region [26.0g/L], kappa/lambda ratio 6.42) was referred for follow-up of stage 3/4 chronic kidney disease presumed secondary to vasculopathy. Over three years, his sCr fluctuated between 90 and 240umol/L. There were no clinical precipitants for these fluctuations. It was subsequently noted that the lower sCr readings were from samples processed at an external laboratory that used an enzymatic assay, rather than the Jaffe method used locally. To determine the patient’s true kidney function, a single specimen was processed by both the Jaffe (213umol/L) and enzymatic (110umol/L) methods at our local laboratory. A concurrent 24-hour urine collection demonstrated creatinine excretion of 14mmol/day, correlating to a creatinine of 115umol/L.
Conclusions
IgM paraproteins may positively interfere with sCr measured by the Jaffe method, contrasting with existing case reports of IgM interference with enzymatic methods. Clinicians should be cognisant of unexplained fluctuations in sCr, understanding the potential limitations of commonly used assays, and speak with their respective laboratory staff for assistance as needed. Access to both laboratory creatinine assays is crucial in investigating clinically discrepant results.
Biography:
Bio to come