Heterophilic antibody interference in a non-endogenous molecule assay: An apparent elevation in the tacrolimus concentration

Puzzling Interference in the Siemens Tacrolimus Assay in a Renal Transplant Patient: A Case Report

BACKGROUND

Therapeutic drug monitoring is a key tool for optimizing tacrolimus therapy in transplant recipients. The modified ACMIA assay from Siemens Healthcare Diagnostics is an immunoassay commonly used for tacrolimus monitoring, but it is not known whether this assay is resistant to interference from endogenous substances in real-world use.

OBJECTIVE

To describe a case of unexpected interference in tacrolimus monitoring using the modified ACMIA method in a kidney transplant recipient, and to highlight the importance of careful interpretation of laboratory results and effective communication with clinicians in optimizing patient care.

CASE DESCRIPTION

This case report describes a significant interference in the monitoring of tacrolimus in a kidney transplant recipient using the new ACMIA method. In this case, when aberrant results for tacrolimus were found using the new ACMIA method, they were re-analyzed using the CMIA method from Abbott. The presence of positive ANCA-MPO autoantibodies was found to be the most likely cause of the interference after an extensive workup.

CONCLUSIONS

This is the first report of major interference with the modified ACMIA tacrolimus method and emphasizes the importance of proper interpretation of laboratory results and effective communication with clinicians in optimizing patient care.

Effects of Broad Spectrum Antibiotics on Measurement of Immunosuppressant Drugs

BACKGROUND

Antibiotics used parenterally can affect blood drug level measurements, as measured in diagnostic tests.

OBJECTIVE

To investigate the effect of six different antibiotics commonly used in intensive care units on tacrolimus, sirolimus, everolimus and cyclosporin A levels measured by mass spectrometry.

METHODS

Ampicillin + sulbactam (AB1, IV, 1 g), imipenem + cilastatin sodium (AB2, IV, 500 mg), piperacillin + tazobactam (AB3, 4.5 g, IV), ertapenem (AB4, IV, 1 g), meropenem trihydrate (AB5, 500 mg, IV) and ceftriaxone (AB6, 1 g, IV) antibiotics were used for the interference assay. Measurements were performed on the Shimadzu 8045 (Japan) LC-MS/MS instrument. Bias values were calculated.

RESULTS

The least affected immunosuppressant was cyclosporine A (between -6.88% and 3.40%). The most affected were everolimus and sirolimus. Ertapenem caused negative interference on the level of everolimus at the rate of -27.34% and sirolimus at the rate of -26.79%. Piperacillin + tazobactam and imipenem + cilastatin sodium caused positive interferences on sirolimus at the rate of 24.24% and 22.73%, respectively. Ampicillin + sulbactam, meropenem trihydrate and ceftriaxone affected the sirolimus levels at lower rates (-4.49%, 5.93% and 9.86%). Everolimus levels deviated at the rate of -11.21% to -16.99% due to imipenem + cilastatin sodium, meropenem trihydrate and ceftriaxone.

CONCLUSION

This study demonstrated the potential of antibiotic use affecting immunosuppressant levels. Antibiotic interference, especially in transplant patients, may cause erroneous immunosuppression, increasing the likelihood of rejection.

False Immunosuppressant Measurement by LC-MS/MS Method Due to Radiopaque Agents

BACKGROUND

Although liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) is preferred as a reliable method, some molecules in the blood matrix may lead to false positive or false negative results. False positive or negative results show the direction of the deviation rate from the target value.

AIM

The aim of this study was to investigate the effect of seven different radiopaque agents on four immunosuppressant drugs.

METHODS

Every agent coded with RM1 to RM7 was added to control materials containing tacrolimus, everolimus, sirolimus, and cyclosporine A drugs. Measurements were performed using an LC-MS/MS instrument. Bias values were calculated to detect the deviation rates.

RESULTS

All RMs led to false negative results in the tacrolimus and cyclosporine A levels at a rate of -19.77% (95% CI, -27.16 to 12.52) to -44.45% (95% CI, -49.20 to -39.69). The smallest deviations were seen in the everolimus levels with the administration of RM6 (gadodiamide) and in the sirolimus levels with RM1 (gadobutrol) at the rates of 4.04% (95% CI, -11.36 to -3.17) and 2.11% (95% CI, -7.18 to 7.11), respectively. The most affected drug by RM4 (gadopentetate dimeglumine salt) was sirolimus at the rate of 114.01% (95% CI, 97.31 - 130.76). RM5 (gadodiamide) interfered cyclosporine A at the most. The highest deviations were observed with the administration of RM3 (iohexol) in the everolimus and sirolimus levels at the rates of 153.72% (95% CI, 142.44 to 164.78) and 171.41% (95% CI, 157.91 to 184.97), respectively.

CONCLUSION

Radiopaque agents interfered the measurement of immunosuppressant drugs. Especially, everolimus and sirolimus levels were affected due to using iohexol. The choice of gadodiamide or ioversol is important to reduce the risk of interference for everolimus measurement. The blood samples should be obtained for measurement of drug levels before contrast-enhanced imaging.

False Elevation of the Blood Tacrolimus Concentration, as Assessed by an Affinity Column-mediated Immunoassay (ACMIA), Led to Acute T Cell-mediated Rejection after Kidney Transplantation

Tacrolimus is the most commonly used immunosuppressant. Because of its narrow therapeutic range, it is necessary to frequently monitor its concentration. We report the case of a 25-year-old man who underwent kidney transplantation whose tacrolimus concentrations, as measured by an affinity column-mediated immunoassay, were falsely elevated. As we reduced the dose of tacrolimus, the recipient developed T cell-mediated rejection. Using the same blood samples, an enzyme-multiplied immunoassay technique showed that the patient's levels of tacrolimus were extremely low. A further examination indicated that the false increase in the tacrolimus concentration was likely due to an unknown interfering substance. We administered methylprednisolone and antithymocyte-globulin. The patient's serum creatinine level decreased and remained stable after these treatments.

Heterogeneous and homogeneous immunoassays for drug analysis

Immunoassays are very useful techniques to perform screening and semi-quantitative analysis of hundreds of different xenobiotics. Small sample volumes are required and pretreatment is usually unnecessary (e.g., homogeneous immunoassays). Fully automated and high-throughput systems are available, which help physicians to take timely decisions. However, immunoassays do suffer from interference from both endogenous and exogenous factors that limit their application in quantitative analysis. These assays use different labels (e.g., colorimetric, fluorescent, chemiluminescent or electrochemiluminescent) and different methods for generating and measuring signals, but the basic principles are usually similar. This review outlines the practical aspects of immunoassays in bioanalysis and describes their application in clinical chemistry for xenobiotic analysis, namely medicines and drugs of abuse.

False tacrolimus concentrations measured by antibody-conjugated magnetic immunoassay in liver transplant patient: 2 case reports and literature review

Safe use of tacrolimus relies on regular whole-blood drug monitoring. Of the methods used to assess whole-blood tacrolimus concentration, antibody-conjugated magnetic immunoassay is mostly used for therapeutic drug monitoring because it requires only a minimal sample preparation and no pretreatment procedure. However, several cases recently have been reported in which abnormally false elevated tacrolimus concentrations were measured by antibody-conjugated magnetic immunoassay (>15 ng/mL), despite the absence of clinical symptoms. We present 2 cases of falsely detected tacrolimus concentrations that did not show abnormally high values within the therapeutic range. Whole-blood tacrolimus concentrations obtained by antibody-conjugated magnetic immunoassay showed well-controlled concentrations (approximately 2-8 ng/mL), whereas those obtained by another immunoassay and in washed erythrocytes were below the assay range (< 1.2 ng/mL). Thus, antibody-conjugated magnetic immunoassay can elicit falsely positive results of tacrolimus concentrations, even though they are within the therapeutic range.

Standardization of LC-MS for Therapeutic Drug Monitoring of Tacrolimus

BACKGROUND

LC-MS is increasingly used for therapeutic drug monitoring of tacrolimus. A recent summary from an international proficiency-testing scheme demonstrated that the mass spectrometry respondents were the largest method group. However, these methods lack standardization, which may explain the relatively poor interlaboratory agreement for such methods. This study aimed to provide one path toward the standardization of tacrolimus quantification by use of LC-MS.

METHODS

A 40-member whole blood tacrolimus proficiency panel was circulated to 7 laboratories, 4 in the US and 3 in Europe, offering routine LC-MS–based quantification of tacrolimus. All laboratories used a common LC-MS platform and followed the manufacturer's instructions that accompanied an LC-MS reagent kit intended for tacrolimus quantification in whole blood samples. Four patient pools were prepared that had sufficient volume to allow comparison with a tacrolimus reference measurement procedure.

RESULTS

For the 40-member panel, the standardized MassTrak LC-MS assay demonstrated excellent agreement with a validated LC-MS method used by Analytical Services International (y = 1.02x − 0.02; r = 0.99). The CVs for the pooled patient samples ranged from 2.0% to 5.4%. The mean difference from the reference measurement procedure ranged from 0.4% to 4.4%.

CONCLUSIONS

Tacrolimus assay standardization, which must include all facets of the analysis, is necessary to compare patient results between laboratories and to interpret consensus guidelines. LC-MS can provide accurate and precise measurement of tacrolimus between laboratories.

Impact of interferences including metabolite crossreactivity on therapeutic drug monitoring results

Therapeutic drug monitoring is an integral part of services offered by toxicology laboratories because certain drugs require routine monitoring for dosage adjustment to achieve optimal therapeutic response and avoid adverse drug reactions. Immunoassays are widely used for therapeutic drug monitoring. However, immunoassays suffer from interferences from both exogenous and endogenous compounds including metabolites of the parent drug. Digoxin immunoassays are affected more commonly than any other immunoassays used for therapeutic drug monitoring. Digoxin immunoassays are affected by endogenous digoxin-like immunoreactive substances and exogenous compounds such as various drugs, certain herbal supplements, and Digibind. Carbamazepine is metabolized to carbamazepine 10, 11-epoxide, and the crossreactivity of this metabolite with carbamazepine immunoassay may vary from 0% to 94%. Immunoassays used for measuring concentrations of tricyclic antidepressants are affected by tricyclic antidepressant metabolites and by a number of other drugs. Immunoassays for immunosuppressants are also subjected to significant interferences from metabolites, and liquid chromatography combined with mass spectrometry or tandem mass spectrometry is recommended for therapeutic drug monitoring of immunosuppressants. However, liquid chromatography combined with mass spectrometry may also suffer from interferences, for example, due to ion suppression or from isobaric ions.

Ligand binding assays in the 21st century laboratory: recommendations for characterization and supply of critical reagents

Critical reagents are essential components of ligand binding assays (LBAs) and are utilized throughout the process of drug discovery, development, and post-marketing monitoring. Successful lifecycle management of LBA critical reagents minimizes assay performance problems caused by declining reagent activity and can mitigate the risk of delays during preclinical and clinical studies. Proactive reagent management assures adequate supply. It also assures that the quality of critical reagents is appropriate and consistent for the intended LBA use throughout all stages of the drug development process. This manuscript summarizes the key considerations for the generation, production, characterization, qualification, documentation, and management of critical reagents in LBAs, with recommendations for antibodies (monoclonal and polyclonal), engineered proteins, peptides, and their conjugates. Recommendations are given for each reagent type on basic and optional characterization profiles, expiration dates and storage temperatures, and investment in a knowledge database system. These recommendations represent a consensus among the authors and should be used to assist bioanalytical laboratories in the implementation of a best practices program for critical reagent life cycle management.

Serum insulin aspart concentrations following high-dose insulin aspart administered directly into the duodenum of healthy subjects: an open-labeled, single-blinded, and uncontrolled exploratory trial

OBJECTIVE

The goal of this study was to determine the bioavailability of high-dose insulin aspart administered directly into the duodenum of healthy subjects.

METHODS

In a pilot study, four subjects each received four escalating doses of a 1-ml solution of insulin aspart (100, 300, 600, and 1000 IU, respectively) directly into the duodenum. In the following main study, eight subjects each received two identical doses of insulin aspart of 1000 IU, in 4- and 8-ml solutions, respectively, directly into the duodenum. Subjects in the main study also received an intravenous and a subcutaneous injection of 4 to 6 IU of insulin aspart.

RESULTS

A considerable number of samples and, in some cases, consecutive samples revealed significantly increased concentrations of serum insulin aspart. Despite the significant serum insulin aspart concentrations, no significant changes of plasma glucose were measured. Moreover, no significant suppression of endogenous insulin secretion was detected, as assessed by the levels of serum human insulin.

CONCLUSIONS

Administration of high-dose insulin aspart directly into the duodenum of healthy subjects resulted in significantly increased serum insulin aspart concentrations in a high number of consecutive samples using a specific enzyme-linked immunosorbent assay. However, no significant changes in the levels of plasma glucose or serum human insulin were observed. Thus, the study did not provide any evidence of biological activity of the original insulin aspart molecule after high-dose administration directly into the duodenum.

Performance characteristics of laboratory testing and clinical outcomes

In order to demonstrate the relationship between performance characteristics of laboratory tests and clinical outcomes, diabetes seems to represent a paradigmatic disease: diagnosis, monitoring of therapeutic efficacy and prognosis are adequately achieved by means of laboratory testing. Starting from a simple molecule, glucose, used for the diagnosis of diabetes, continuing with creatinine, used for monitoring renal function in diabetic patients and concluding with cardiac troponins, a recognised gold standard for the diagnosis and risk stratification of cardiovascular diseases, several criticisms may be stressed considering the current methodological state-of-the art. Finally, an often overlooked aspect of performance, the analytical interferences, being responsible of unexpected results, that in turn depend from unknown or undisclosed factors will be discussed, concerning in particular, in our paper, the macroprolactin and the heterophilic antibodies aspects.