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

Understanding the limitations of your assay using EQA data with serum creatinine as an example

OBJECTIVES

Laboratories need to take into consideration the specificity and imprecision of assays not only in verification, but also of quality assessment. This study investigates the composition of serum used in EQA materials by comparing material from a single and multiple donors (pooled material), across multiple methods, using creatinine as an example.

METHODS

Sixteen different serum matrices were distributed as 36 specimens through the UK NEQAS for Acute and Chronic Kidney Disease Scheme from March 2022 to March 2023. Male-only and female-only serum was used as single donations, pooled donations, unmanipulated or with added exogenous creatinine. Specimens were distributed to primarily UK participants (approximately n=500) for creatinine analysis. Data has been reviewed by method compared to the enzymatic creatinine method principle mean.

RESULTS

From the 16 different matrices, only the enzymatic creatinine assay systems from Roche Cobas and Siemens Atellica met the minimum acceptable bias goal, from biological data, of 5.6 %, in all specimens. Pooled material showed less variation in bias across all methods.

CONCLUSIONS

Since Laboratories invest a lot of time and money in quality management, they need to know the limitations of their assays so that they are not investigating 'apparent' EQA/IQC problems which are purely due to non-specific, imprecise assay, rather than an analytical issue in their laboratory. When large numbers of individual donations are combined, interferents are essentially diluted out. Therefore, if EQA material is of this type it will be very difficult to determine the actual assay's bias and variability.

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.

Emergency medicine pharmacotherapy compromises accuracy of plasma creatinine determination by enzyme-based methods: real-world clinical evidence and implications for clinical practice

Background

Assessment of kidney function in emergency settings is essential across all medical subspecialties. Daily assessment of patient creatinine results from emergency medical services showed that some deviated from expected values, implying drug-related interference.

Methods

Real-time clinical evaluation of an enzyme method (Roche CREP2) in comparison with the Jaffé gen. 2 method (Roche CREJ2) was performed. During the period of December 2022 and January 2023, we analyzed 8,498 patient samples, where 5,524 were heavily medicated STAT patient specimens, 500 were pediatric specimens, and 2,474 were from a distant general population in a different region using the same methods.

Results

In 109 out of 5,524 hospital specimens (1.97%, p < 0.001), the CREP2 value was apparently (25% or more) lower than CREJ2. Suspect interfering medication was found in a sample of 43 out of 46 reviewed patients where medication data were available. This phenomenon was not observed in the general population.

Conclusion

In a polymedicated urgent care hospital population, a creatinine enzyme method produces unreliable results, apparently due to multiple drug-related interferences.

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.

Effect of serum creatinine difference between the Jaffe and the enzymatic method on kidney disease detection and staging

Background

Serum creatinine (SCr), mainly determined by the Jaffe or an enzymatic method, is the central marker to assess kidney function. Deviations between these two methods may affect the diagnosis and staging of acute kidney injury (AKI) and chronic kidney disease (CKD).

Methods

The results of the first parallel SCr measurement (Jaffe and enzymatic method) of adult in- and outpatients in the same serum sample at the University Hospital Essen (Essen, Germany) between 2020-2022 were retrospectively evaluated. A Bland-Altman plot with 95% limits of agreement (LoAs) was used to assess the difference between the Jaffe and the enzymatic SCr (eSCr) method. We used the 2009 Chronic Kidney Disease Epidemiology Collaboration equation for determination of estimated glomerular filtration rate (eGFR) according to the Kidney Disease: Improving Global Outcomes guidelines.

Results

A total of 41 144 parallel SCr measurements were evaluated. On average, Jaffe SCr was 0.07 mg/dl higher than eSCr (LoA -0.12; 0.25 mg/dl). In 19% of all cases there was a different CKD stage when comparing eGFR between both SCr methods, of which 98% resulted in a more severe CKD stage determined with Jaffe SCr. In 1.6% of all cases Jaffe SCr was ≥0.3 mg/dl higher than eSCr.

Conclusion

The present study showed that methods of SCr measurement may affect both the diagnosis and staging of AKI and CKD. This must be taken into account when interpreting measurements of renal function in everyday clinical practice, but also when planning and comparing studies on renal diseases. One should therefore stay with one method for SCr measurement, preferably with the enzymatic method.

Diagnostic challenges of diabetic kidney disease

Diabetic kidney disease (DKD) is one of the most common microvascular complications of both type 1 and type 2 diabetes and the most common cause of the end-stage renal disease (ESRD). It has been evidenced that targeted interventions at an early stage of DKD can efficiently prevent or delay the progression of kidney failure and improve patient outcomes. Therefore, regular screening for DKD has become one of the fundamental principles of diabetes care. Long-established biomarkers such as serum-creatinine-based estimates of glomerular filtration rate and albuminuria are currently the cornerstone of diagnosis and risk stratification in routine clinical practice. However, their immanent biological limitations and analytical variations may influence the clinical interpretation of the results. Recently proposed new predictive equations without the variable of race, together with the evidence on better accuracy of combined serum creatinine and cystatin C equations, and both race- and sex-free cystatin C-based equation, have enabled an improvement in the detection of DKD, but also require the harmonization of the recommended laboratory tests, wider availability of cystatin C testing and specific approach in various populations. Considering the complex pathophysiology of DKD, particularly in type 2 diabetes, a panel of biomarkers is needed to classify patients in terms of the rate of disease progression and/or response to specific interventions. With a personalized approach to diagnosis and treatment, in the future, it will be possible to respond to DKD better and enable improved outcomes for numerous patients worldwide.

Spurious laboratory results associated with immunoglobulin M gammopathy in a dog with multiple myeloma

An 11 year old female-neutered Labrador presented for facial swelling. Clinicopathological abnormalities included hyperglobulinemia, azotemia, hypercalcemia, nonregenerative anemia, thrombocytopenia, and spurious hypoglycemia. Normoglycemia was subsequently confirmed using a cage-side analyzer (AlphaTRAK, Zoetis, UK). Serum and urine protein electrophoresis documented monoclonal (immunoglobulin M) gammopathy with Bence-Jones proteinuria. Computed tomography imaging revealed a monostotic osteolytic bone-lesion, and bone marrow cytology and histopathology documented plasmacytosis with multiple myeloma oncogene 1 / interferon regulatory factor 4 positivity, consistent with multiple myeloma. Infectious disease testing initially indicated seropositivity for Leishmania, Borrelia, and Anaplasma spp.; however, Leishmania PCR (splenic and bone marrow aspirates), and paired serological titers for Borrelia and Anaplasma were negative. Consequently, initial serological results were considered to be false positive because of paraproteinemia-associated assay interference. Chemotherapy (prednisolone and melphalan combination therapy) was initiated, but the dog was euthanased 30 days later because of the development of pericardial effusion. This is a report of spurious serological (and other laboratory) results occurring secondary to monoclonal gammopathy in a dog.