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Pseudohypercreatininaemia in two patients caused by monoclonal IgM interference with enzymatic assay of creatinine
  1. Tracey Salter1,
  2. James Marsh1,
  3. Bhrigu Sood1,
  4. Callum Livingstone2,
  5. Hugh Gallagher1
  1. 1 South West Thames Renal and Transplantation Unit, St Helier Hospital, Carshalton, Surrey, UK
  2. 2 Clinical Biochemistry Department, Royal Surrey County Hospital, Guildford, Surrey, UK
  1. Correspondence to Dr Tracey Salter, South West Thames Renal and Transplantation Unit, St Helier Hospital, Wrythe Lane, Carshalton, Surrey SM5 1AA, UK; traceysalter{at}

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Creatinine is released into the blood following non-enzymatic hydrolysis of creatine in skeletal muscle, and excreted into urine depending on glomerular filtration. The serum creatinine concentration is widely used as a marker of glomerular function because it increases in patients with decreased glomerular filtration rate (GFR). Although GFR is costly to measure, an estimated GFR (eGFR) can be calculated from the serum creatinine concentration. Since 2006, laboratories have calculated eGFR values using the isotope dilution mass spectrometry traceable modification of diet in renal disease equation.1 This standardisation allows direct comparison of creatinine and eGFR results from different laboratories. Reporting of eGFR is a significant advance, but it should be remembered that results are affected by interferences affecting the creatinine assay.

Serum creatinine was initially measured for clinical purposes using alkaline picrate (Jaffé reaction),2 but this method is affected by numerous interferents, including bilirubin, ketones, protein and non-creatinine chromogens.3 Enzymatic assays were later introduced, which are less susceptible to interference3 and more specific being unaffected by non-creatinine chromogens.4 However, interference has been reported from 5-fluorocytosine, ethamsylate, dopamine, dobutamine, nitromethane, creatine, sarcosine and ascorbic acid. Hummel et al 5 reported positive interference in enzymatic creatinine measurement caused by monoclonal IgM in three patients with Waldenström's macroglobulinaemia. IgM can precipitate and interfere in the detection step of the reaction. This interference can be avoided by ultrafiltration to remove protein before measuring creatinine. At the time …

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  • Contributors Here, I outline the individual contributions of each coauthor: Myself (TS): I drafted the article, and have been involved in revising it. JM, BS, CL and HG have all revised the article, and given final approval of the version to be published. BS and HG were responsible for the nephrological care of the patients described.

  • Competing interests None declared.

  • Patient consent Obtained.

  • Provenance and peer review Not commissioned; externally peer reviewed.