Falsely Elevated Serum Creatinine Associated With IgM Paraproteinemia

False positive elevation in serum creatinine: a case report

Background

Paraproteins can interfere with several substances, producing erroneous laboratory measurements. The diagnosis of kidney disease in patients with hematological disorders has important prognosis implications. An elevated creatinine with no other signs of kidney disease should prompt the idea of a spurious creatinine. Communication between the clinical team and the laboratory is key.

Case presentation

In this case, we present a 68-year-old woman with an elevated creatinine and an IgM lambda paraprotein. Interestingly, there were no other signs of chronic kidney disease besides the creatinine value, with no albuminuria or microhematuria. A kidney biopsy showed normal parenchyma and ruled out the possibility of paraprotein-related damage. The monoclonal component and creatinine levels raised parallelly during follow-up while maintaining normal urea levels. This prompted the hypothesis of a falsely elevated creatinine. It was confirmed with a normal glomerular filtration rate determined by a radioisotope, a cystatin C measurement and a reduction in creatinine when diluting the sample.

Conclusion

It is important to consider the possibility of a falsely elevated creatinine in patients with paraproteinemia and no other signs of kidney disease to avoid unnecessary diagnostic tests and for the prognostic implications.

Artefactually low creatinine by Beckman Coulter enzymatic method due to immunoglobulin M paraprotein interference

An 81-year-old man was admitted to hospital with symptomatic coronavirus disease (COVID-19) infection. He had a background of progressive chronic inflammatory demyelinating polyneuropathy associated with Waldenstrom's macroglobulinaemia. His plasma creatinine on four separate samples was inconceivably low (all ≤13 μmol/L), as measured by a Beckman Coulter enzymatic assay) after being 72 μmol/L 3 months earlier. On further investigation, his serum immunoglobulin M (IgM) was 15.4 g/L and his plasma creatinine measured by Roche enzymatic and Roche Jaffe methods was 62 μmol/L and 64 μmol/L, respectively. This was consistent with results post dilution studies and polyethylene glycol (PEG) precipitation on the Beckman Coulter assay. There was no evidence of similar interference when reviewing creatinine results from 10 other patients with IgM paraproteinaemia who had been tested in our laboratory. Clinicians and laboratorians are reminded that enzymatic creatinine is not free from interferences. IgM paraprotein negative interference of enzymatic creatinine is rare and specific to a patient's IgM and assay combination, but should be considered in patients with an unexplained low enzymatic creatinine result. Useful investigations to identify an interference include dilution studies, PEG precipitation and measuring creatinine on an alternative method such as Jaffe, mass spectrometry or an enzymatic method from a different platform.

Negative interference from immunoglobulin M paraproteinaemia on the Roche enzymatic creatinine method

Although enzymatic creatinine methods are subject to fewer interferences than traditional Jaffe creatinine methods, every method in clinical chemistry has limitations. We report, for the first time in the literature, a case of an immunoglobulin M (IgM) paraproteinaemia causing an undetectably low creatinine result on the Roche enzymatic assay. This interference did not occur with other enzymatic creatinine methods produced by Abbott and Siemens or the Roche Jaffe, VITROS dry slide and liquid chromatography with tandem mass spectrometry (LC-MS/MS) creatinine methods. IgM interference was confirmed as patient serum precipitated with polyethylene glycol (PEG) and anti-IgM antiserum yielded detectable Roche enzymatic creatinine results comparable to unaffected methods. The patient's serum formed an obvious precipitate when mixed with reagent one of the Roche enzymatic creatinine method. This is in contrast to a report of positive interference from IgM paraproteinaemia in a different enzymatic creatinine method, which showed that a precipitate formed when mixing blood with reagent two. As each patient's paraprotein has a unique structure, it is possible that there are variations in the chemical characteristics of IgM paraproteins between patients. This, as well as IgM-class antibodies' tendency to form multimers and aggregates, can lead to unpredictable assay interferences and precipitation tendencies between different manufacturers of enzymatic creatinine reagents and their incubation steps. This case highlights the importance of continuing to question and investigates results that do not fit the clinical picture, especially as more laboratories switch from primarily using traditional Jaffe creatinine methods to enzymatic creatinine methods.