Deciphering an Unexpected Serum Creatinine Result in a Critically Ill Patient

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1 CASE REPORTS SC Deciphering an Unexpected Serum Creatinine Result in a Critically Ill Patient Charlton Agius 1 * and Gerald Buhagiar 1 CASE DESCRIPTION A 74-year-old man with acute congestive cardiac failure complicated by cardiogenic shock came for emergency care. He required admission to the coronary care unit because of circulatory collapse and was given inotropic support with simultaneous intravenous infusions of dopamine and dobutamine. These medications were administered via a central line. An unexpected change in the patient's serial serum creatinine (SCr) resulted in a >60% change within 24 h (71 μmol/l/0.8 mg/dl from the earlier 186 μmol/l/2.1 mg/dl; reference interval μmol/l/ mg/dl). However, other surrogate markers of renal function (urea and potassium) did not show the same magnitude of variability in their measurements (Fig. 1). The isolated change affecting 1 analyte did not suggest a dilutional effect by sample contamination. Preanalytical errors related to sample misidentification were excluded, and serum indices did not indicate the possibility of hemolysis, icterus, or lipemia interference. Another urgent blood sample was requested, and this was reanalyzed with the same methods used previously for urea, SCr, and potassium. The repeat results yielded values for SCr of 66 μmol/l/0.75 mg/dl, urea of 31 mmol/l/87 mg/dl urea nitrogen (reference interval <11.9 mmol/l/<71 mg/dl), and potassium of 3.3 mmol/l (reference interval mmol/l), which were comparable with previous measurements obtained. Clinicians noted no improvement in the patient's clinical condition and no change in his drug therapy except for escalation of the infusion rates for administered inotropes on day 15 of his hospital admission. An alternative method using a compensated kinetic Jaffe assay was performed on the samples showing the unexpected SCr results, and a marked difference in results between the 2 methods was noted (Table 1). Results from the Jaffe method were comparable with the patient's day 15 postadmission SCr measurements; thus, possible negative interference in the enzymatic-based creatinine method was suspected. Liaison with the coronary care unit staff confirmed that the last 2 blood samples were collected from the patient's central venous catheter because of difficult peripheral venous access. Incidentally this was also the site of administration of the inotropic drugs dopamine and dobutamine. Based on the preanalytical site of sample collection and the different SCr results obtained from using the Jaffe method as opposed to the enzymatic SCr method of analysis, the patient's catecholamine-based therapy was implicated as being the possible interferent. Therefore, a switch to Jaffe-based results was necessary to provide further assessment and monitoring of his renal function; however, the patient died on day 17 after hospital admission. 1 Department of Pathology, Clinical Chemistry Section, Mater Dei Hospital, Msida, Malta. *Address correspondence to this author at: Department of Pathology, Clinical Chemistry Section, Mater Dei Hospital, Msida, Malta. charlton.agius@gov.mt. DOI: /jalm American Association for Clinical Chemistry JALM :03 November 2017

2 Case Report CASE REPORTS Fig. 1. Patient serum creatinine (SCr), urea (Ur), and potassium (K) results over the period of hospitalization in the intensive care unit. All SCr measurements were performed with same enzymatic-based method. Reference intervals for SCr, μmol/l/ mg/dl; Ur, <11.9 mmol/l/<71 mg/dl; and K, mmol/l. All analytes were obtained in VACUETTE serum separator tubes containing clot activator and serum separator gel. Analysis was performed on a Roche Cobas c501 automated analyzer platform (Roche Diagnostics) with reagent kits supplied from the same manufacturer. SCr was assayed using an enzymatic method based on 4- aminophenazone to generate a quinone imine chromogen. Alternative creatinine measurements were performed using a compensated buffered kinetic Jaffe reaction without deproteinization. Urea was analyzed using a urease and glutamate dehydrogenase kinetic-based method. Potassium was analyzed using a neutral carrier indirect ion-selective electrode. DISCUSSION SCr measurements are routinely used as a surrogate marker for the assessment of renal function, and are also frequently incorporated in SCr-based equations to provide an estimated Table 1. Comparison of kinetic and enzymatic creatinine values. SCr (enzymatic method) a SCr (kinetic Jaffe method) a Percentage difference between results (%) First sample 71 μmol/l (0.8 mg/dl) 210 μmol/l (2.38 mg/dl) 66 Repeat sample 66 μmol/l (0.75 mg/dl) 200 μmol/l (2.26 mg/dl) 67 a SCr reference interval, μmol/l ( mg/dl).... November : JALM 431

3 CASE REPORTS Case Report glomerular filtration rate. The use of an SCr method that has calibration traceable to an isotope-dilution mass spectrometry reference measurement procedure has been advocated by standardization and harmonization campaigns in an attempt to provide more reliable SCr measurements and glomerular filtration rate estimation by reducing the source of variation caused by calibration bias (1). However, standardization of calibration does not correct for nonspecificity bias by analytical interferences of field methods. The use of enzymatic-based assays that are more specific for SCr determination than the long-established alkaline picrate-based (Jaffe) methods is also supported by international efforts (2). Enzymatic methods, although less susceptible to noncreatinine chromogen interference, are still subject to clinically significant interferences, as this case illustrates; however, when compared with the Jaffe methods, the enzymatic assays offer more specific SCr determination with improved accuracy, producing results that agree closely with isotope-dilution mass spectrometry even after potential elimination of the calibration error by alignment of Jaffe assays with isotope-dilution mass spectrometry (2). Better precision for SCr measurements may also be afforded with the enzymatic methods, as well as the added benefit of appearing to produce reliable results when delays in sample processing defers blood centrifugation for 24 h or more (2). Although the adoption of enzymatic methods into routine practice is based on robust and widely accepted evidence, these have, to date, still not completely replaced Jaffe-based methods. The main reason for this may be the perceived higher commercial costs of reagents for enzymatic assays; however, this may be a false objection because the increase in the number of enzymatic assays by competing vendors will likely reduce prices in the near future, and these costs are also likely to be outweighed in the context of wider health economics (2). This case illustrates a well-established but significant interference in enzymatic SCr determination by the catecholamines dopamine and dobutamine. Negative interference by these 2 amines has been previously reported with other assays, including glucose, uric acid, cholesterol, and triglycerides, using methods that utilize a peroxide/ peroxidase system based on the reaction originally described by Trinder to generate quinone-imine dyes (3, 4). Two distinct mechanisms for dopamine and dobutamine interference occurring with peroxidase-based assays have been described. Dopamine interferes stoichiometrically with methods that use 4-aminophenazone to form a chromophore but shows minimal interference in methods that use other compounds to generate a chromophore. As a result, a novel peroxideimine dye is formed when dopamine reacts with 4-aminophenazone in the presence of peroxide and peroxidase. This dye has a smaller absorptivity than the chromophore formed in the absence of dopamine, thus resulting in the negative interference observed by reducing the total absorbance at the wavelength used to measure the analyte. Contrary to dopamine, dobutamine interferes stoichiometrically with all peroxidase-based tests, regardless of whether 4-aminophenazone is used to form the chromophore, by being rapidly oxidized by peroxide in the presence of peroxidase, thus depleting the peroxide necessary to generate chromophore (4). Epinephrine and norepinephrine also produce a negative interference in enzymatic SCr values at low molar ratios when in vitro spiked solutions of these drugs are added to patient sera; however, these 2 catecholamines show minimal differences (<5%) in creatinine values when paired catheter and venipuncture samples from patients receiving epinephrine and norepinephrine are collected, suggesting that these catecholamines do not adhere to indwelling catheters (5). Point-of-care enzymatic methods that make use of peroxidase to determine the concentration of JALM :03 November 2017

4 Case Report CASE REPORTS creatinine have also been shown to be susceptible to catecholamine interference with dopamine and dobutamine when spiked solutions of the drugs were added to patient sera (5). Very significant positive interference from dopamine has been noted with the i-stat method but not with the StatStrip method. Whereas dobutamine had no significant effect using the i-stat method, a negative bias with the StatStrip method was shown to be present, and this increased with the increase in the dobutamine concentration (6). The interference observed in routine clinical practice is largely a preanalytical error whereby minor intravenous fluid contamination of samples with dopamine and dobutamine can result in clinically significant interferences (4). This is observed only with samples obtained from sites of indwelling catheters where there is concomitant intravenous administration of these drug solutions and not with peripheral blood sampling remote from the site of drug administration (6). The interference does not occur with in vivo steady-state plasma concentrations of both these drugs as levels reach <1 mg/l, even when multiple catecholamine agents are administered simultaneously (8 10). Catecholamines are widely used intravenous therapeutic agents in critically ill patients with refractory decompensated cardiac failure and cardiogenic shock. Thus, misleading and inaccurate results caused by catecholamine interferences are arguably more clinically significant for SCr because the patient population receiving this particular drug therapy requires more frequent biochemical assessment of their renal function because they are more vulnerable to worsening of their kidney function and, as a consequence, also have higher mortality rates (7). To circumvent this well-established interference, the first step should be avoidance of preanalytical error by instructing service users to avoid blood draws from catheters that are used for administering dopamine and/or dobutamine infusions. If this is practically challenging, for example, TAKEAWAYS Dopamine interferes with methods that use 4-aminophenazone to form a chromophore but shows minimal interference in methods that use other compounds to generate a chromophore, whereas dobutamine interferes with all peroxidase-based tests regardless of whether 4-aminophenazone is used to form the chromophore. The catecholamine interference is primarily a preanalytical error, and service users require adequate instruction on proper sample collection procedures to prevent contamination of blood samples with these drug solutions. This is achieved largely by avoiding sample collection from sites of drug administration. Contrary to Jaffe methods, most enzymatic-based methods for SCr measurement used in clinical practice are susceptible to such interference. This has serious clinical implications for critically ill patients who are receiving therapy with these drugs and require regular biochemical assessment of their renal function. Clinicians and laboratory professionals should be mindful of this interference, and meaningful deciphering of any clinically suspected falsely low SCr result may be afforded if the laboratory makes use of 2 SCr methods (enzymatic and Jaffe) to cross-check questionable results, especially with the use intelligent information solutions to proactively detect and route investigations to suitable platforms. Alternatively, other markers of renal function such as serum cystatin C may be used in these cases.... November : JALM 433

5 CASE REPORTS Case Report if other sites of collection are unavailable, it is worth considering the addition of other SCr methods that are not prone to interference from catecholamines in the laboratory test repertoire offered to these patients, such as Jaffe-based or alternative enzymatic methods free from this interference (5). Otherwise, a different renal marker altogether, such as serum cystatin C, may be used. Although the latter assay is more expensive, cystatin C has been shown to be a better marker of renal function in early stages of acute kidney injury and is less affected by age, sex, muscle mass, and ethnicity. The use of urea as a substitute for SCr or cystatin C as a stand-alone renal marker is not feasible because it is well known that various confounding factors limit its use and thus can vary independently of the glomerular filtration rate. A combination of markers increases diagnostic accuracy in both acute and chronic settings of renal dysfunction but comes at an obvious cost that may not be afforded in routine clinical practice (11). If resources permit the use of information technology solutions, then these may also be used to proactively identify and manage this issue, whereby the patient's medications are scanned for The situation thus highlights the continued need for laboratories, especially those supporting intensive care facilities, to offer a combination of assays for the assessment of renal function in critically ill patients, for whom an inaccurate result may lead to serious untoward consequences. catecholamines when a hospitalized patient has an electrolyte panel or creatinine ordered, and if the patient is taking any catecholamine medications known to cause interference, the specimen will be routed to the appropriate platform having a suitable method that is free from interference for analysis (5). SUMMARY This case demonstrates negative interference in enzymatic SCr measurement occurring in a critically ill patient. This is a preanalytical error resulting from intravenous fluid contamination of serum samples with dopamine and dobutamine solutions. Author Contributions: All authors confirmed they have contributed to the intellectual content of this paper and have met the following 4 requirements: (a) significant contributions to the conception and design, acquisition of data, or analysis and interpretation of data; (b) drafting or revising the article for intellectual content; (c) final approval of the published article; and (d) agreement to be accountable for all aspects of the article thus ensuring that questions related to the accuracy or integrity of any part of the article are appropriately investigated and resolved. Authors Disclosures or Potential Conflicts of Interest: No authors declared any potential conflicts of interest. REFERENCES 1. Myers GL, Miller WG, Coresh J, Fleming J, Greenberg N, Greene T, et al. Recommendations for improving serum creatinine measurement: a report from the Laboratory Working Group of the National Kidney Disease Education Program. Clin Chem 2006;52: Panteghini M, on behalf of the IFCC Scientific Division. Enzymatic assays for creatinine: time for action. Clin Chem Lab Med 2008;46: Trinder P. Determination of glucose in blood using oxidase with an alternative oxygen acceptor. Ann Clin Biochem 1969;6: Karon BS, Daly TM, Scott MG. Mechanisms of dopamine and dobutamine interference in biochemical tests that use peroxide and peroxidase to generate chromophore. Clin Chem 1998;44: Saenger AK, Lockwood C, Snozek CL, Milz TC, Karon BS, Scott MG, Jaffe AS. Catecholamine interference in enzymatic creatinine assays. Clin Chem 2009;55: JALM :03 November 2017

6 Case Report CASE REPORTS 6. Dimeski G, Tilley V, Jones B, Brown N. Which point-ofcare creatinine analyser for radiology: direct comparison of the i-stat and StatStrip creatinine methods with different sample types. Ann Clin Biochem 2012;50: Rafouli-Stergiou P, Parissis J, Anastasiou-Nana M. Inotropes for the management of acute heart failure patients with renal dysfunction. Still an option? Expert Opin Pharmacother 2012;13: Schwartz PH, Eldadah MK, Newth CJL. The pharmacokinetics of dobutamine in pediatric intensive care unit patients. Drug Metab Dispos 1991; 19: Banner W, Vernon DD, Dean JM, Swenson E. Nonlinear dopamine pharmacokinetics in pediatric patients. J Pharmacol Exp Ther 1989;249: Fisher DG, Schwartz PH, Davis AL. Pharmacokinetics of exogenous epinephrine in critically ill children. Crit Care Med 1993;21: Wasung ME, Chawla LS, Madero M. Biomarkers of renal function, which and when? Clin Chim Acta 2015; 438: November : JALM 435