Comparison of fluorescence polarization immunoassay and high performance liquid chromatography for the quantitative determination of phenytoin, phenobarbitone and carbamazepine in serum

The Abbott TDx fluorescence polarization immunoassay (FPIA) system has been evaluated and compared with well-established high performance liquid chromatography (HPLC) for the determination of three anticonvulsant drugs: phenytoin, phenobarbitone and carbamazepine. These assays were evaluated for precision, calibration curve stability, specificity and accuracy. Within-run precision studies using control samples (n = 15) in the subtherapeutic, therapeutic, and toxic concentrations, resulted in coefficients of variation in the range of 1.79-3.99% (FPIA) and 1.16-2.52% (HPLC), respectively. Between-run precision ranged from 2.32-6.34% for FPIA and from 2.04-3.38% for HPLC. Comparison of 122 patient samples assayed with both methods indicated an extremely good analytical correlation (r = 0.96) for all three comparisons. The FPIA method offers significant advantages in calibration curve stability while maintaining accuracy and precision comparable with those of established HPLC procedures.     

酶扩大免疫测定技术与荧光偏振免疫法测定全血环孢素浓度的比较

目的:比较酶扩大免疫测定技术(EMIT)与荧光偏振免疫法(FPIA)测定全血环孢素浓度的差异。方法:通过分别测定高、中、低浓度标准质控品评价各方法的准确度及精密度,并对卫生部室间质控品及99份临床全血环孢素样本进行测定,比较2种方法测定结果的相关性。结果:EMIT与FPIA方法学的相对回收率分别在93.74%～105.73%与99.84%～102.26%之间,日内及日间精密度良好,RSD均小于10%,符合生物样品的测定要求。两方法测定结果具有良好的相关性Y=1.122 1 X+1.783 7,r=0.987,EMIT的测定结果大多低于FPIA测定结果。结论:EMIT法与FPIA法测定环孢素血药浓度结果存在显著性差异,临床应用中应予以关注并作相应调整。     

Evaluation of an enzyme immunochromatography method for carbamazepine: a comparison with enzyme-multiplied immunoassay technique, fluorescence polarization immunoassay, and high-performance liquid chromatography

A noninstrumented enzyme immunochromatography (EIC) method for monitoring carbamazepine using whole blood was compared to the enzyme-multiplied immunoassay technique (EMIT), fluorescence polarization immunoassay (FPIA), and high-performance liquid chromatography (HPLC). Samples from 74 patients were evaluated in the comparison study, yielding correlation coefficients of 0.961 (EMIT), 0.974 (FPIA), and 0.867 (HPLC). The EIC method produced within-run coefficients of variation of 4.3%, 4.9%, and 5.8% for three carbamazepine concentrations. The between-run coefficient of variation over 107 days was 4.9%. The spiked serum sample analysis yielded recovery rates ranging from 98 to 102%. Enzyme immunochromatography was found to be a useful noninstrumented method for on-site testing. The test gives quantitative patient sample results comparable to the results obtained using established laboratory methods.     

Specific enzyme-multiplied immunoassay and fluorescence polarization immunoassay for cyclosporin compared with Cyclotrac [125I]radioimmunoassay.

The analysis of cyclosporin-A (CsA) has proved a valuable adjunct to clinical care of patients who have received organ grafts. The measurement of CsA in whole blood by specific methods has recently taken a new direction with the introduction of a range of rapid methods, including a homogeneous enzyme immunoassay technique (EMIT) and a monoclonal fluorescence polarization immunoassay (FPIA). The present paper compares these two methods with the established Cyclotrac specific [125I]RIA (radioimmunoassay) using both commercial CsA-spiked control material as well as a group of 60 patient specimens (predominantly renal transplants). While each of the new methods showed acceptable precision and accuracy with the commercial quality control material, significant differences were demonstrated with patient specimens, such that FPIA was 12.5% greater than [125I]RIA (p less than 0.0001), which was in turn 5.9% greater than EMIT (p = 0.007). These data suggested that the FPIA may have residual CsA-metabolite interference and that the EMIT method was the most "specific" for parent CsA of the three tested, potentially therefore more comparable to high-performance liquid chromatography (HPLC).     

Measurement of cyclosporine in plasma of cardiac allograft recipients by fluorescence polarization immunoassay

The Abbott TDx fluorescence polarization immunoassay (FPIA) procedure for measuring cyclosporine A (CsA) was evaluated and compared with the Sandoz polyclonal radioimmunoassay (CsA RIA kit) method. This drug assay was evaluated for precision, calibration, stability, and accuracy. Within-run precision studies utilizing 25 replicate analyses of the three control preparations (containing CsA in the 60-800 ng/ml range) resulted in coefficients of variation (CV) ranging from 1.0 to 9.1%. The CVs of between-run precision determined by assaying the same control drug levels for five consecutive working days ranged from 3.9 to 4.6%. Calibration curve stability was assessed by examining the drift in control values over a 2-week period. Maximum plasma ranged from 82.6 to 108.2%. Four hundred plasma samples were obtained from 30 heart-transplant patients during the first 6 months of CsA therapy and each sample was analyzed simultaneously by TDx and RIA. Linear regression analysis of the results obtained for each patient (x = RIA, y = FPIA) revealed the following mean values: r = 0.87, (CV = 13.7%), slope = 1.47 (CV = 39.2%). Moreover, the concentration of CsA was determined in 35 patient samples both by TDx and high-performance liquid chromatography (HPLC). FPIA results up to 12 times higher than HPLC results have been noted.     

Evaluation of fluorescence polarization immunoassay for determination of cyclosporin in plasma

The fluorescence polarization immunoassay (FPIA) method for determination of cyclosporin in plasma was evaluated and compared with the high-performance liquid chromatography (HPLC) and the radioimmunoassay (RIA) methods. The coefficients of variation for the within-run and between-run precision were less than 5 and less than 8%, respectively, for samples ranging in concentration from 50 to 600 ng/ml. Recoveries were determined by adding cyclosporin at concentrations from 25 to 1,000 ng/ml to patient plasma; they were, on average, 98.5%. The calibration curve was stable throughout a 10-week study period. There was no clinically significant interference due to hemolysis, icterus, lipemia, or other commonly used drugs. There was considerable variation of the ratio of the FPIA result to the HPLC result, whereas there was a good correlation between the FPIA and the RIA results (r = 0.975, n = 25, y = 1.2x - 36.4), when evaluated using specimens from renal transplant patients receiving cyclosporin orally. It was concluded that the FPIA is an appropriate, rapid method for patient cyclosporin analysis in plasma and serves as a practical alternative to the RIA.     

Potential problem with fluorescence polarization immunoassay cross-reactivity to vancomycin degradation product CDP-1: its detection in sera of renally impaired patients

During the development of a homogeneous immunoassay for the antibiotic vancomycin, we observed in certain patient samples a quantitation difference between the enzyme multiplied immunoassay technique (EMIT) method and the comparison method, fluorescence polarization immunoassay (FPIA). This prompted us to evaluate the integrity of vancomycin in samples from renally impaired patients. Since it has been reported in the scientific literature that vancomycin degrades into an antibiotically inactive crystalline degradation product (CDP-1) in vitro, we developed high-performance liquid chromatography (HPLC) and liquid chromatography/mass spectrometry (LC/MS) methods to determine whether CDP-1 is present in patient sera. HPLC and LC/MS analysis on samples from renally impaired patients positively identified CDP-1 in fresh samples. Next, we tested the cross-reactivity of three currently available vancomycin immunoassays, radioimmunoassay (RIA) FPIA, and EMIT, to CDP-1 prepared in our laboratory. Our data suggest that CDP-1 is recognized by FPIA and RIA, both polyclonal antibody-based methods, but not by EMIT, which uses a monoclonal antibody.     

三种检测方法测定甲氨蝶呤血药浓度的比较分析

目的比较高效液相色谱法（HPLC）、荧光偏振免疫分析法（FPIA）和酶增强免疫法（EMIT）监测甲氨蝶呤（MTX）血浆药物浓度的相关性。方法收集接受大剂量甲氨蝶呤化疗后的患者的血液样品,分别用HPLC、FPIA和EMIT法进行测定,考察3种测定方法的相关程度。结果多配对样本Friedman检验提示3种方法间差异有显著性,Wilcoxon检验结果提示HPLC法和FPIA法检测结果之间差异无显著性,EMIT法结果与另外两种方法之间差异有显著性。3种检测方法的的回归分析结果为：Y HPLC=1.00X FPIA＋0.015（r=0.978,P〈0.000 1）;Y HPLC=0.94X EMIT-0.079（r=0.956,P〈0.000 1）;Y FPIA=0.95X EMIT-0.089（r=0.927,P〈0.000 1）。结论 3种甲氨蝶呤检测方法之间还是存在差异,但这种差异是可以预见性的,且可以通过换算消除,临床治疗和研究工作要予以注意。     

Analytical performance of the CEDIA cyclosporine PLUS whole blood immunoassay

Cyclosporine A (CsA) is a potent immunosuppressive agent used in solid organ and bone marrow transplantation. Because of the narrow therapeutic range and variable pharmacokinetics, blood levels of CsA are routinely monitored. The performance of the CEDIA CsA PLUS whole blood immunoassay was evaluated on the Olympus AU400 trade mark, and results were compared to those obtained by high-performance liquid chromatography (HPLC), enzyme-multiplied immunoassay technique (EMIT), and fluorescence polarization immunoassay (FPIA). A total of 592 whole blood samples from patients receiving CsA were tested by each of the assays. CEDIA was linear from 25 to 2000 micro g/L. Total imprecision ranged from 2.7% to 8.7% at CsA values between 48 and 1502 micro g/L. Recovery of added CsA was within 10% of assigned values and was unaffected by bilirubin and lipemia. Metabolite cross-reactivity at 500 micro g/L was 8.1% for AM1, 21.7% for AM4n, and 32.5% for AM9. Regression analysis revealed the following: HPLC = 0.93. CEDIA - 21.2 (r = 0.975), EMIT = 1.08. CEDIA - 25.2 (r = 0.982), and FPIA = 1.14. CEDIA + 13.4 (r = 0.984). CEDIA has acceptable analytical performance for routine CsA monitoring. Advantages are the absence of an extraction step and an extended measuring range. The disadvantage is the high metabolite cross-reactivity; however, results were similar to EMIT     

Comparison of the fluorescence polarization immunoassay and the microbiological assay methods for the determination of gentamicin concentration in human serum

The performance of the fluorescence polarization immunoassay (FPIA) was compared with that of a microbiological assay for the measurement of serum gentamicin concentrations. Within-run precision from duplicate assays of two concentrations (4 and 8 micrograms/ml) using FPIA and the microbiological assay yielded coefficients of variation (r) of 2.62%, 1.76% (n = 12) and 8.06%, 6.87% (n = 12), respectively. Day-to-day precision was estimated by repetitive analysis of 4 and 8 micrograms/ml control samples over a 3-week period. Coefficients of variation (r) were 2.57%, 3.09% (n = 8) and 10.71%, 14.20% (n = 8) for FPIA and the microbiological assay, respectively. Linear regression analysis performed on data from parallel determinations on 143 patient samples by the two methods showed correlations in the order of 0.74. The FPIA offers a rapid, efficient, and accurate system for therapeutic monitoring of gentamicin serum levels.     

Evaluation of caffeine plasma levels by an automated enzyme immunoassay (EMIT) in comparison with a high-performance liquid chromatographic method

A new enzyme immunoassay (EMIT) for the measurement of levels of caffeine in plasma was adapted to an automated centrifugal analyzer (Cobas Bio) and compared with a high-performance liquid chromatographic (HPLC) method. Precision of the EMIT test was similar to that of the HPLC method with intraassay coefficients of variation in the range of 2.0-4.1% (EMIT) and 1.5-3.3% (HPLC), respectively, depending on the concentration range tested. Day-to-day precision ranged from 2.7 to 5.6% for EMIT and was 3% for HPLC. Comparison of 69 patient samples assayed with both methods yielded the following equation: y = 1.06x + 1.25 mumol/L, r = 0.994 (X = HPLC, y = EMIT). Evaluation of the cross-reactivity of the three main human caffeine metabolites revealed no significant interference from theobromine and theophylline; however, there was significant interference (28%) by paraxanthine at a concentration range from 2.5 to 80 mumol/L. At low caffeine concentrations, up to 10 mumol/L, the level of this metabolite may be more than twice the corresponding caffeine concentration; therefore, the latter may be falsely elevated in the EMIT test. Despite this cross-reactivity, the new EMIT test proved to be suitable for use in a drug assay laboratory, as well as in the routine screening of outpatients for liver disease.     

Validation of a high-pressure liquid chromatography and fluorescence polarization immunoassay for the determination of methadone in canine plasma

Methadone is a synthetic opiate derivative that possesses analgesic activity. A modified fluorescence polarization immunoassay (FPIA) method and a high-pressure liquid chromatography (HPLC) method with UV detection were compared for measurement of concentrations of methadone in canine plasma following intravenous and oral methadone administration. The mean+/-SD for accuracy (deviation from actual concentration) and precision (coefficient of variation) when methadone-fortified canine plasma was evaluated with the FPIA method were 3.9+/-3.2% and 4.4+/-2.9%, respectively. The accuracy and precision of the HPLC method were 6.2+/-5.2% and 7.7+/-3.9%, respectively. The limit of quantification for the FPIA and HPLC methods were 25 and 20 ng/mL, respectively. The coefficient of determination (r) between FPIA and HPLC analysis was 0.94 when plasma from dogs dosed with methadone was evaluated. FPIA provides a rapid, sensitive, and specific measurement of methadone in canine plasma following oral and intravenous administration.     

Methotrexate measurements in plasma: comparison of enzyme multiplied immunoassay technique, TDx fluorescence polarization immunoassay, and high pressure liquid chromatography

One hundred nine patient plasma samples were examined for methotrexate (MTX) levels by enzyme multiplied immunoassay technique (EMIT), fluorescence polarization immunoassay (TDx), and high pressure liquid chromatography (HPLC). EMIT analysis was performed twice within a time span of 18 months. All three methods measure MTX with a high degree of specificity, sensitivity, and precision. There was no evidence of decay of MTX concentrations in samples stored at -20 degrees C for 1.5 years. EMIT, TDx, and HPLC are adequate methods for MTX quantification in the clinical laboratory.     

EMIT和FPIA测定丙戊酸、甲氨喋呤和环孢霉素A血药浓度的比较研究

目的比较均相酶放大免疫分析法(EMIT)和荧光偏振免疫分析法(FPIA)测定丙戊酸(VPA)、甲氨喋呤(MTX)和环孢霉素A(CsA)血药浓度结果,并评价两种测定方法所得结果的相关性。方法收集患者服药后的血样,采用EMIT和FPIA同时测定VPA、MTX和CsA血药浓度;以FPIA测定值为X,以EMIT测定值为Y,进行线性回归,评价其相关性。结果所得线性回归方程如下:YVPA=1.894 1+1.190 3X,r=0.983;YMTX=0.099 24+1.136X,r=0.992;YCsA=1.146 5+0.846 1X,r=0.971。EMIT测定血浆中VPA血药浓度较FPIA高11.2μg.mL 1,EMIT测定MTX血药浓度较FPIA高0.22μmol.L 1,EMIT测定CsA血药浓度较FPIA低20.6 ng.mL 1,差异有统计学意义(P<0.05)。结论 EMIT与FPIA测定VPA、MTX和CsA血药浓度差异具有统计学意义,在治疗药物监测中应予以注意。     

CMIA、FPIA、MEIA与EMIT测定血药浓度的比较分析

目的：分析比较化学发光微粒子免疫分析法（CMIA）、荧光偏振免疫分析法（FPIA）、微粒子捕捉免疫分析法（MEIA）和酶扩大免疫分析法（EMIT）测定血清丙戊酸（VPA）、全血环孢霉素A（CsA）、血清卡马西平（CBZ）和血清地高辛（DIG）浓度的一致性。方法：通过测定高、中、低浓度质控样品,评价各方法的准确度及精密度,并对临床患者的VPA、CsA、CBZ和DIG样本进行测定,比较4种方法测定结果的相关性。结果：CMIA与EMIT（测定值为函数Y）比较,测定VPA的结果具有良好的相关性和差异性,Y_EMIT=1.172X_CMIA+0.227（r=0.97）,EMIT的测定结果比CMIA平均高17.49%。FPIA与EMIT比较,测定结果具有良好的相关性：VPA,Y_EMIT=1.259X_FPIA-4.671（r=0.97）;CsA,Y_EMIT=0.832X_FPIA+17.63（r=0.97）;CBZ,Y_EMIT=1.156X_FPIA-2.657（r=0.98）;MEIA与EMIT比较,测定结果有相关性：DIG,Y_EMIT=0.634X_MEIA+0.018（r=0.91）;其中CsA的EMIT测定结果比FPIA平均低2.08%,DIG的EMIT测定结果比MEIA平均低35.91%,而VPA的EMIT测定结果比FPIA平均高16.83%、CBZ的EMIT测定结果比FPIA平均高3.07%。结论：CMIA测定VPA血药浓度、FPIA测定VPA、CsA、CBZ及MEIA测定DIG血药浓度与EMIT的测定结果,存在差异性（P<0.05）,临床应用中应予以关注并作相应调整。     

Analytic validation of the enzyme multiplied immunoassay technique for the determination of mycophenolic acid in plasma from renal transplant recipients compared with a high-performance liquid chromatographic assay.

The analysis of mycophenolic acid (MPA) has proved a valuable adjunct to the clinical care of organ transplant recipients. The analytic validation of the enzyme multiplied immunoassay technique (EMIT) for the determination of MPA in plasma is described. The EMIT MPA standard curve was 0 to 15.0 microg/mL, and curve storage was maintained for 4 weeks. The MPA EMIT assay proved reliable and reproducible, as shown by the intra-assay and interassay coefficients of variation (1.58-3.68% and 1.23-7.57%, respectively). Excellent linear correlation ( r = 0.999) was observed for dilution linearity. The sensitivity of the assay was 0.01 microg/mL. Recoveries of 99.4% to 104.2% were obtained by spiking aliquots of three controls of known MPA concentrations with MPA. No interference was observed for endogenous substances and coadministered immunosuppressant drugs, and no cross-reactivity from the major metabolite MPA glucuronide was found. The high-performance liquid chromatography (HPLC) assay used protein precipitation and C18 ion-pair chromatography with ultraviolet detection at 304 nm. Plasma concentrations of MPA were measured using EMIT and HPLC. A linear relationship was observed between EMIT and HPLC (EMIT = 1.091 x HPLC - 0.089; r 2 = 0.990, n = 129). These results indicate that EMIT is a simple, rapid, and sensitive assay method for the measurement of MPA in plasma.     

Pentobarbital quantitation using immunoassays in Reye's syndrome patient serum

Analysis of serum pentobarbital concentrations in 28 specimens from Reye's syndrome patients was conducted with modifications of three nonspecific immunoassay procedures originally designed to detect barbiturates in serum or urine. An adaptation of the urine enzyme-multiplied immunoassay technique (EMIT) Dupont aca barbiturate screen to the quantitation of serum pentobarbital is described. Replicate analysis of control specimens containing pentobarbital across a wide spectrum of concentrations revealed a between-day precision of less than 6%. Regression analysis revealed excellent agreement with a high-performance liquid chromatography (HPLC) method: (HPLC) = 0.98 (aca) - 0.07 (r = 0.97). Multiple linear regression analysis with a serum EMIT barbiturate screen and a urine fluorescence polarization immunoassay screen modified to quantitate pentobarbital in serum revealed excellent agreement among all methods, demonstrating that immunoassays offer a reliable approach to pentobarbital quantitation.     

Evaluation of a mouse monoclonal antibody for the determination of serum theophylline by fluorescence polarization immunoassay

Theophylline concentrations in spiked human serum and serum specimens obtained from patients with normal and impaired renal function were measured by fluorescence polarization immunoassay (FPIA) using a mouse monoclonal antitheophylline antibody. The interday coefficients of variation of the assay after 14 days were 4.2, 3.3, and 2.4% at serum theophylline concentrations in pooled human serum of 7.1, 12.2 and 26.9 mg/L. Theophylline concentrations determined by FPIA and high performance liquid chromatography (HPLC) were used to generate the following linear regression equations relating the corresponding theophylline concentrations measured by each method in serum specimens from 50 patients with normal renal function (FPIA = 1.00 HPLC + 1.01, r = 0.98) and 50 patients with end-stage renal disease (FPIA = 1.04 HPLC + 0.08, r = 0.99). In contrast to previous studies performed with a polyclonal antitheophylline antibody, the precision, accuracy, and specificity of the FPIA were adequate for analysis of theophylline in serum specimens obtained from patients with end-stage renal disease.     

测定环孢素全血浓度的2种方法对比及临床应用

目的对比荧光偏振免疫法(FPIA)和均相酶扩大免疫分析法(EMIT)2种测定方法监测环孢素(CsA)血药浓度的差异。方法收集98例次环孢素全血样品,同日同一患者的全血样品分别采用FPIA和EMIT法测定血药浓度。结果 EMIT和FPIA测定结果相关系数r为0.9795,EMIT法较FPIA法平均低(11±12)%(P<0.05,n=98),其中CsA血药谷值浓度(c_0)EMIT法较FPIA法平均低(14±9)%(P<0.05,n=69)。CsA血药峰值浓度(c_2)EMIT法较FPIA法平均低(2±5)%(P>0.05,n=29)。结论 2种不同方法测定全血中CsA血药浓度具有显著差异,EMIT法较FPIA法具有较高的特异性。     

A comparison of EMIT and FPIA methods for the detection of cyclosporin A blood levels: does impaired liver function make a difference?

Objective: Apparent cyclosporin A (CSA) blood levels, as determined by fluorescence polarization immunoassay (FPIA) and enzyme-multiplied immunoassay technique (EMIT), were compared in CSA-treated patients with various degrees of liver dysfunction. Methods: FPIA and EMIT were performed in parallel according to test manufacturer instructions in blood from kidney (n=82), liver (n=96) and heart transplant (n=20) patients. Results: The precision of both techniques was greatest in patients with the highest blood levels, and at each blood level greater for the FPIA than for the EMIT. Apparent CSA blood levels, as determined by EMIT, were typically approximately 70% of those determined by FPIA, indicating greater cross-reaction of the antibody in the FPIA with CSA metabolites. However, the ratio of values determined with EMIT and FPIA was very similar in kidney, liver and heart transplant patients. Among liver transplant patients it was also very similar in those without major alterations of hepatic function and in those with impaired excretory (increased bilirubin and γGT) or synthetic (i.e., reduced thromboplastin time) function. Extended storage of blood samples for up to 10 days did not affect apparent CSA blood level estimates by EMIT in a clinically relevant manner. Conclusions: We conclude that the greater specificity of the antibody in the EMIT for the CSA parent compound does not translate into a clinically relevant advantage for CSA monitoring. Received: 20 September 1996 / Accepted in revised form: 17 February 1997