Pseudohypercreatininemia due to positive interference in enzymatic creatinine measurements caused by monoclonal IgM in patients with Waldenström's macroglobulinemia

Discrepant serum creatinine concentrations caused by paraprotein interference preceding diagnosis of monoclonal gammopathy of undetermined significance

We report a man in his 70s who presented with discrepant serum creatinine concentrations in different hospitals at the same time. Further examinations of these discrepancies revealed turbidity of the serum sample and, thus, a reagent reaction and false hypercreatinine caused by paraprotein interference were suspected. Serum protein electrophoresis revealed a small amount of monoclonal γ globulin (2.9 g/L), which may have been involved in paraprotein interference. Monoclonal λ-type IgG was detected in the serum, resulting in a diagnosis of monoclonal gammopathy of undetermined significance. Previous studies indicated paraprotein interference in serum containing monoclonal IgM or a large amount of IgG (> 25 g/L). Although this case of paraprotein interference induced by a small amount of IgG is rare, a discrepancy in creatinine results may be an indicator leading to the diagnosis of plasma cell proliferative diseases.

Pseudohypercreatininemia after surgery for aortic dissection: a case report

BACKGROUND

Elevated creatinine concentrations often indicate acute renal injury and renal biopsies are considered in this situation. However,pseudohypercreatininemia is potential cause of elevated creatinine concentrations, and invasive interventions should be avoided.

CASE PRESENTATION

A 54-year-old woman underwent surgery for descending aortic dissection.Nine days postoperatively, her creatinine concentration increased from 1 mg/dl to 5.78 mg/dl (normal range, 0.47-0.7 mg/dl). Azotemia and hyperkalemia were absent and physical examination findings were unremarkable. Cystatin C concentration was 1.56 mg/l (normal range, 0.56-0.8 mg/l) and pseudohypercreatininemia was suspected. Testing with different reagents showed a creatinine concentration of 0.84 mg/dl. Immunoglobulin (Ig)G was markedly elevated, and creatinine and IgG fluctuated in parallel, suggesting the cause of the pseudohypercreatininemia. IgG4 was also elevated at 844 mg/dl. Immunosuppressive steroid therapy effectively decreased the IgG concentration and resolved the pseudohypercreatininemia.

CONCLUSIONS

In cases of elevated creatinine concentration with the presence of abnormal proteins, pseudohypercreatininemia should be considered. We report a rare case of pseudohypercreatininemia caused by polyclonal IgG.

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.

PSEUDOHYPOPHOSPHATEMIA IN A PATIENT WITH MULTIPLE MYELOMA

Objective

To discuss the diagnosis and management of paraprotein interference in the setting of multiple myeloma (MM).

Methods

We discuss the evaluation of hypophosphatemia in a patient with MM and present a review of the relevant literature.

Results

Our patient, who had a history of MM, was found to have persistently undetectable serum phosphate which did not respond to aggressive phosphate replacement. His clinical condition was not consistent with severe phosphate depletion and hence paraprotein interference secondary to MM was suspected. Re-analyzation of samples on a different machine showed normal serum inorganic phosphate levels.

Conclusion

Paraprotein interference from MM causing pseudohypophosphatemia can be overlooked and lead to unnecessary treatment. Recognition of this phenomenon is important to all clinicians, especially in light of potential complications of unnecessary treatment.

Clinical and Analytical Impact of Moving from Jaffe to Enzymatic Serum Creatinine Methodology

Background

Identification and monitoring of chronic kidney disease (CKD) requires accurate quantification of serum creatinine. The poor specificity of Jaffe creatinine methods is well documented, and guidelines recommend enzymatic methodology. We describe our experience of moving from Jaffe to enzymatic creatinine methodology. We present comparison of >5000 paired Jaffe and enzymatic creatinine results, examine interferences, and attempt to assess clinical consequences of changing methodology.

Methods

Overall, 5303 serum samples received for routine creatinine measurement were analyzed using Jaffe and enzymatic methods with an Abbott Architect autoanalyzer. Associated results for glucose, total bilirubin, triglycerides, total protein, and hemolytic, icteric, and lipemic indexes were extracted from the laboratory database. CKD staging was estimated for each sample to assess potential clinical effects.

Results

The methods correlated well (r = 0.996) and showed good agreement (Passing-Bablok fit, y = 0.935x + 0.074). Paired analysis, however, showed significant differences (P < 0.001), and approximately 20% of results differed by more than ±10%. Multivariate analysis demonstrated independent associations between difference in creatinine results, glucose (P < 0.0001), and hemolytic index (P = 0.009). Glucose demonstrated positive interference in the Jaffe method, and hemolysis produced negative interference in the enzymatic method. Little or no association was observed with other analytes. CKD staging differed in 4% of samples.

Conclusions

Differences between Jaffe and enzymatic serum creatinine results exceed the recommended 5% target for a significant proportion of samples, particularly at concentrations <1.13 mg/dL (100 µmol/L). Both glucose and hemolysis contribute to the variance in results. Although the clinical impact of these differences seems small, laboratories should continue moving toward enzymatic creatinine estimation to ensure the best estimate of renal function.

Unusual manifestation of monoclonal gammopathy of undetermined significance: a false serum creatinine elevation

A 72-year-old Japanese man with diabetes mellitus and hypertension presented with an acutely elevated serum creatinine level, from 1.02 to 4.13 mg/dL over 2 months as measured by the enzymatic method by pure-auto S CRE-N^®. Renal biopsy could not identify the etiology of the elevating sCr. However, an elevated total protein level (8.2 g/dL) and lowering of the BUN and sCr ratio from 14.5 to 2.7 were found, and bone marrow biopsy showed less than 10% lymphoplasmacytic infiltration, compatible with monoclonal gammopathy of undetermined significance. The diagnosis of a false serum creatinine elevation due to monoclonal gammopathy of undetermined significance was confirmed with the serum cystatin C level at 1.05 mg/dL and the creatinine level of 0.97 mg/dL using Shikarikid-S CRE^® method. Although cases of monoclonal gammopathy of undetermined significance with a false serum creatinine elevation as an initial presentation are rare, this condition should be considered in patients with paraproteinemia; measuring the renal function using cystatin C is important in such patients.

Deceiving proteins! A case of lymphoma and high creatinine

Estimation of kidney function by measuring serum creatinine is one the commonest laboratory tests conducted in clinical practice. Enzymatic methods are often used to measure serum creatinine. Clinicians should be aware of the limitations of these methods, such as test interference with paraproteins.We present a case of falsely elevated serum creatinine in a patient referred for renal biopsy. The combination of fluctuating creatinine and normal blood urea level was unusual. Serum protein electrophoresis revealed the presence of an IgM paraprotein. Further investigations confirmed an underlying diagnosis of lymphoplasmacytoid lymphoma. This case highlights how IgM paraprotein can interfere with creatinine estimation by enzymatic assay and the utility of alternative methods of estimating serum creatinine.

Falsely Elevated Plasma Creatinine Due to an Immunoglobulin M Paraprotein

The most common method for measuring plasma creatinine is based on its reaction with picric acid. However, enzymatic methods are becoming more popular due to improved specificity. We present a case of falsely elevated plasma creatinine values obtained by an enzymatic method that turned out to be due to a monoclonal immunoglobulin M (IgM) paraprotein. A 63-year-old woman evaluated for lung transplantation had falsely increased plasma creatinine levels (1.54-1.71mg/dL; corresponding to estimated glomerular filtration rates of 32-36 mL/min/1.73m²) as measured by the Roche Creatinine plus enzymatic assay when compared with the picric acid-based procedure and several other enzymatic methods, which gave plasma creatinine values of 0.7 to 0.8mg/dL. Serum protein electrophoresis revealed an IgM κ light chain paraprotein. Removal of high-molecular-weight (>30kDa) proteins by ultrafiltration reduced the patient's plasma creatinine level by the Roche enzymatic method to 0.7mg/dL. Addition of the patient's immunoglobulin fraction to plasma from other patients with normal plasma creatinine levels resulted in values that were increased by 0.58 to 0.62mg/dL. Furthermore, removal of non-IgM immunoglobulins with protein G-coupled beads did not eliminate the interference from the patient's plasma. Taken together, these studies demonstrate that falsely elevated plasma creatinine values by the Roche enzymatic method can be due to an IgM paraprotein.

The pH of chemistry assays plays an important role in monoclonal immunoglobulin interferences

Objectives

Immunoglobulin paraproteins can interfere with multiple chemistry assays. We want to investigate the mechanisms of immunoglobulin interference.

Design and methods

Serum samples containing paraproteins from the index patient and eight additional patients were used to investigate the interference with the creatinine and total protein assays on the Beckman Coulter AU5400/2700 analyzer, and to determine the effects of pH and ionic strength on the precipitation of different immunoglobulins in these patient samples.

Results

The paraprotein interference with the creatinine and total protein assays was caused by the precipitation of IgM paraprotein in the index patient's samples under alkaline assay conditions. At extremely high pH (12–13) and extremely low pH (1–2) and low ionic strength, paraprotein formed large aggregates in samples from the index patient but not from other patients.

Conclusions

The pH and ionic strength are the key factors that contribute to protein aggregation and precipitation which interfere with the creatinine and total protein measurements on AU5400/2700. The different amino acid sequence of each monoclonal paraprotein will determine the pH and ionic strength at which the paraprotein will precipitate.

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Investigation of the cause of IgM paraprotein interference with creatinine assay.

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Paraprotein precipitation under assay conditions caused the interference.

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Identified The pH of chemistry assays is a key factor causing paraprotein precipitation.

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Results showed that not all paraproteins precipitate under the same assay conditions.

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Different paraproteins react differently to changes in pH and ionic strength.

Paraproteins are a common cause of interferences with automated chemistry methods

CONTEXT

Previous studies have shown that paraproteins caused spurious results on individual analytes including total bilirubin (TBIL), direct bilirubin (DBIL), or HDL-cholesterol (HDL-C). Studies demonstrating paraprotein interferences with multiple analytes measured by different analyzers have not been reported.

OBJECTIVE

To systemically investigate interferences of paraproteins on TBIL, DBIL, and HDL-C measured by the Roche MODULAR and the Olympus AU2700.

DESIGN

Eighty-eight serum specimens with monoclonal gammopathies were analyzed using the Roche MODULAR and the Olympus AU2700. Paraprotein interferences with the MODULAR and AU2700 were identified by abnormal absorbance curves and confirmed by results from the Ortho Vitros 950 or inconsistent laboratory information.

RESULTS

Spurious results occurred in 89 of 528 measurements; 29 specimens did not demonstrate any interferences whereas 26 specimens gave spurious results in 2 to 4 of the 6 assays. Paraprotein interferences caused spuriously high levels of TBIL in 4 sera measured by the MODULAR. In contrast, paraprotein interferences on DBIL were observed by at least 1 method in 44% (39/88) of sera assayed, occurring almost exclusively with the AU2700. Paraprotein interferences with HDL-C results were present in 35% of specimens assayed with the MODULAR and 16% of specimens assayed with the AU2700. In specimens with interferences, spuriously low AU2700 DBIL, MODULAR HDL-C, and AU2700 HDL-C results occurred with 28%, 90%, and 91% of specimens, respectively.

CONCLUSIONS

We demonstrated that paraprotein interferences with TBIL, DBIL, and HDL-C are relatively common and provided explanations why these interferences occurred. Although it is difficult to predict which specimens cause interferences, spurious results appeared method and concentration dependent.

Protein precipitation as a possible important pitfall in the clinical chemistry analysis of blood samples containing monoclonal immunoglobulins: 2 case reports and a review of the literature

Two case reports are presented, both illustrating an analytical interference caused by monoclonal immunoglobulins. Falsely low results were obtained in the routine analysis of glucose, CRP and HDL-cholesterol. When analysing samples containing paraproteins, various problems can be encountered in the clinical laboratory: next to the antibody effect, pseudohyponatraemia, hyperviscosity, cryoglobulinaemia and gel formation have to be taken into account. In our two cases the interference was caused by paraprotein precipitation, causing an increased turbidity and an apparent increase of light absorbance at every wavelength due to light scattering, including the wavelengths used in the clinical chemistry assays. We review the literature on this sometimes overlooked interference in photometric/turbidimetric assays. This reaction is based on the insolubility of these proteins in specific physico-chemical circumstances in which many variables are involved, among others: pH and ionic strength, presence of preservatives and surfactants in the assays, pI and other specific properties of the monoclonal immunoglobulins. The complexity of the problem makes predicting or preventing this probably infrequent interference usually impossible. This artifact can cause both false positive and false negative results in multiple parameters (e.g. bilirubin, creatinine, iron, urea, uric acid), the most frequently reported analyte being phosphate. The Sia water test (Sia euglobulin precipitation test) can provide a first clue to a paraprotein aggregation; confirmation can be obtained by observing the time/ absorbance curves of the analysis, performing the test manually or setting up a serial dilution of the sample. The problem can be solved by avoiding the presence of the proteins in the assay, performing the analysis using an alternative method or diluting out the interference. Both laboratorians and clinicians should be aware of interferences in the clinical laboratory since the clinical consequences could be important.

Artifactual hyperbilirubinemia due to paraprotein interference

CONTEXT

Paraprotein interference in automated chemistry is uncommon. We describe 2 patients with paraproteinemia and elevated total bilirubin levels measured erroneously using the Roche total bilirubin assay.

OBJECTIVES

To explain the mechanism of this artifactual hyperbilirubinemia and to determine its frequency in patients with monoclonal or increased immunoglobulins.

MATERIALS AND METHODS

The assay was performed manually using serum from 2 index patients and from control patients (without M proteins). Total bilirubin was also determined using another manufacturer's assay. A prospective study was then undertaken using serum from 100 consecutive patients with various monoclonal gammopathies and from 13 patients with polyclonal hypergammaglobulinemia and cryoglobulins. For all patients, serum immunoglobulin (Ig) G, IgA, IgM, total and direct bilirubin, creatinine, and a direct spectrophotometric assessment of icterus were measured.

RESULTS

After the addition of assay reagents, a white precipitate formed in the reaction mixtures containing serum from the index patients, but not in other samples. This turbidity, rather than the expected color change to pink, increased the absorbance and falsely elevated the total bilirubin value. Serum from both index patients was anicteric, their direct bilirubin measurements were unaffected, and total bilirubin measured using an alternate assay was normal. Among the 113 patients studied, no additional spurious total bilirubin values were detected.

CONCLUSION

Paraprotein interference with the Roche automated total bilirubin assay is caused by precipitate formation. This interference is rare and probably idiosyncratic. Spurious hyperbilirubinemia from paraprotein interference may cause clinical confusion. If artifactual elevation of total bilirubin is suspected, the laboratory should examine the specimen for icterus (manually or by spectrophotometry) or measure total bilirubin using a different method.