Automated latex nephelometric immunoassay for the measurement of serum lipoprotein (a)

A sensitive immunoassay based on latex particle agglutination has been developed for measuring lipoprotein Lp(a) concentrations in serum or plasma. Carboxylated latex particles (diameter 240 nm) covalently coated with F(ab')₂ fragments of anti-lipoprotein Lp(a) antibodies are incubated with diluted sample (400-fold) for 12 min at room temperature, with the resulting agglutination quantified by measuring the change of light-scatter produced. The assay has been automated on the Behring nephelometer analyzer with a sampling rate of 150 samples/hour. This assay generates a standard curve in the range of 27 to 1750 mg/L, showing inter-assay precision of less than 8%. There were no interferences from plasminogen, bilirubin, Intralipid?, haemoglobin, rheumatoid factor, and apolipoprotein B. No significant differences were observed when fresh and frozen samples were compared. Sample pretreatment with “Lipoclean” clearing agent and sample lyophillization decreased the agglutinating reaction. In two separate studies using 77 and 112 patient sera the Lp(a) values, determined by the latex nephelometric method, the Terumo Macra? Lp(a) ELISA test, and the Pharmacia Apo(a) radioimmunoassay method, gave correlation coefficients of 0.948 and 0.974, respectively. Physiological lipoprotein (a) values were determined in a blood donor group, with the distribution of serum Lp(a) highly skewed, with a mean (SD) and median values of 213(236) mg/L and 116 mg/L, respectively. Concentrations of Lp(a) were found to be age-and sex-independent. This latex nephelometric procedure is a convenient method and an interesting alternative to other immunoassays for routine measurement of human lipoprotein (a). © 1993 Wiley-Liss, Inc.     

Automated quantitative nephelometric latex immunoassay for determining ferritin in human serum.

We describe a rapid and sensitive latex nephelometric immunoassay for quantifying ferritin in human serum. This latex immunoassay procedure uses commercially available ready-for-use reagents [Tina-Quant (a) Ferritin, Boehringer Mannheim] that have a long shelf life. The assay consists of incubating the diluted serum sample (5-fold) for 12 min at room temperature with latex particles covalently coated with anti-ferritin antibodies, and then quantifying the change of light-scatter produced. The assay is fully automated on the Behring nephelometer analyzer with a sampling rate of 150 samples/hour. The method has an analytical range of 3 to 260 micrograms/l. Maximal intra- and inter-assay CVs were 4.0 and 6.2%, respectively. Analytical recoveries ranged from 91.3 to 103.6%. Assay detection limit was less than 3 micrograms/l. Linearity of the test is given throughout the measuring range. There was no interference from bilirubin (up to 340 mumol/l), haemoglobin (up to 7 g/l), or rheumatoid factor (up to 1,100 IU/ml). Turbid and lipemic samples interfere. This interference may be avoided by pretreating these samples prior to assay. Results correlated well with those obtained by an automated ELISA test (r = 0.995) and with those of two commercial RIA methods (r greater than 0.97). This latex nephelometric procedure is a convenient method and represents an interesting alternative to other immunoassays for measuring ferritin in human serum.     

Quantitative automated latex nephelometric immunoassay for determination of myoglobin in human serum

We have evaluated a new latex nephelometric test for the quantitation of myoglobin in human serum. The assay consists of incubating the diluted serum sample (20-fold) for 12 min at room temperature with latex particles covalently coated with anti-myoglobin antibodies and then quantifying the change of light-scatter produced. The assay is fully automated on the Behring nephelometer analyzer with a sampling rate of 150 samples/hour. There is no interference from bilirubin (up to 340 mumol/l), haemoglobin (up to 7,000 mg/l), or rheumatoid factor (up to 1,100 int. units/ml). Myoglobin standard curve extends from 20 to 380 micrograms/l. Assay detection limit lies around 6 micrograms/l. Coefficient of variation ranged from 2.7 to 7.6%. Correlation coefficient between latex immunoassay and an RIA method was 0.987, calculated from the assay of 37 samples. A statistically significant difference was found between the distribution for females and males. The serum level of myoglobin showed an age-dependent variation. Concentrations up to 60 micrograms/l are considered to be normal.     

Evaluation of the Dade Behring N Latex Cystatin C assay on the Dade Behring Nephelometer II System

The Dade Behring N Latex Cystatin C assay, a particle-enhanced nephelometric immunoassay for measuring serum cystatin C, was evaluated on the Dade Behring Nephelometer II. The assay time was 6 min and the throughput was 75 samples per hour. The sample volume was 40 microL and the measuring range was 0.25-7.90 mg/L. Imprecision studies revealed within-run CVs < 1.8% and between-run CVs < 1.8% in the concentration range 0.87-4.63 mg/L. Recovery was 92.4-101.3%. Linearity studies showed excellent correlation between the theoretical and obtained values. No interferences were detected from haemoglobin < 1.0 mmol/ L, bilirubin <512 micromol/L and Intralipid <20 g/L. Stability of cystatin C in serum was 7 days at temperatures from 20 degrees C to 20 degrees C and 6 months at -80 degrees C. Measurements of cystatin C in heparin-plasma and EDTA-plasma did not differ significantly from cystatin C measured in serum. Fifty patient samples run on the Dade Behring Nephelometer II (y) were compared to the Dako Cystatin C assay (x). The Passing-Bablok regression analysis revealed y = 1.105x - 0.340. In conclusion, the Dade Behring N Latex Cystatin C assay was precise and correlated with the Dako Cystatin C assay.     

Microparticle-enhanced nephelometric immunoassay of human plasminogen

A microparticle-enhanced nephelometric immunoassay was developed for plasminogen quantitation in human plasma. It is based on the nephelometric measurement of the light scattered by microparticle clusters formed during a sandwich reaction between plasminogen, microparticle—anti-plasminogen conjugate, and the free antibodies of anti-plasminogen rabbit antiserum. This immunoassay was sensitive (detection limit in reaction mixture, 34 μg/L) and could be performed in 500-fold diluted human plasma, excluding any interference or sample pretreatment. It allowed the quantitation of plasminogen on a large range of concentrations (17–550 mg/L), with a security in antigen excess reaching 1,100 mg/L, with accuracy (linear recovery in dilution-overloading assay and correlation with conventional immunonephelometry), and precision (within- and between-run coefficients of variation lower than 8%). A normal reference range from 54 to 148 mg/L (mean ± 2 SD) was calculated from plasminogen concentration in plasma from 130 adults. Easy to perform (no washing or phase separation) and rapid (two steps of 30 minutes then 1 hour of incubation at room temperature), this microparticle-enhanced nephelometric immunoassay could be an interesting alternative method for human plasminogen quantitation. © 1996 Wiley-Liss, Inc.     

Automated latex nephelometric immunoassay of theophylline in human serum.

A latex test was adapted for the nephelometric quantitation of theophylline in human serum. The assay is fully automated on the Behring Nephelometer Analyser with a sampling rate of 150 samples per hour. There is no interference from bilirubin (up to 340 mumol/l), haemoglobin (up to 7000 mg/l), Intralipid (up to 5 g/l), or rheumatoid factor (up to 1100 x 10(3) IU/l). The theophylline standard curve extends from 1.25 to 40 mg/l. The coefficient of variation ranged from 2.4 to 7.4%. The correlation coefficient between the latex immunoassay and the TDx theophylline procedure was 0.988, calculated from the assay of 74 samples.     

Continuous-flow system for automation of latex immunoassay by particle counting

Latex immunoassay is a nonisotopic method based on agglutination, by protein, of calibrated latex particles coated with a specific antibody. The assay has been automated in a simple continuous-flow system by incubating the reaction mixture in a heated mixing coil for 25 min and measuring the agglutination with a cell counter. No external shaking of the latex suspension and no additional reagent is required for the agglutination. The method can accurately and precisely quantify a wide variety of proteins in plasma and urine, including human ferritin, beta 2-microglobulin, retinol-binding protein, and albumin. Depending on the antigen-antibody system, the detection limit ranges from 10(-10) to about 10(-12) mol/L. Within- and between-assay CVs are less than 10%. In the assay of ferritin, sera are pretreated to eliminate interferences from chylomicrons, complement, and rheumatoid factor.     

Reference interval for serum C-reactive protein in healthy blood donors using the Dade Behring N Latex CRP mono assay

Measurement of the serum concentration of the acute-phase reactant C-reactive protein (CRP) provides an useful objective marker in clinical practice, both in screening for diseases and in monitoring disease activity and response to therapy. The aim of this study was to evaluate the analytical performance of the assay in the concentration range from 0.2 to 15 mg/L, and to determine a reference interval for serum CRP in healthy blood donors using the Dade Behring N Latex CRP mono assay on the Dade Behring Nephelometer II. The assay is a particle-enhanced nephelometric immunoassay with a measuring range of 0.2-1100 mg/L. The sample volume is 40 microL, and the assay time is 6 min. The coefficients of variation for within-run and between-run imprecision studies were between 2.2 and 5.4% in serum pools with CRP concentrations between 1.29 and 11.98 mg/L. Linearity studies showed excellent correlation between the theoretical and the measured values. No interferences were detected from hemoglobin <1.0 mmol/L, bilirubin <512 micromol/L and Intralipid <20 g/L. Blood samples were collected from 268 healthy blood donors (107 females and 161 males) between 20 and 65 years old. The non-parametric reference intervals for serum CRP was calculated to be <0.2-14.7 mg/L in females and <0.2-9.16 mg/L in males. The Mann-Whitney U-test revealed no gender-related difference for serum CRP (p-value=0.72). A common reference interval for serum CRP for both genders was calculated to be <0.2-10.5 mg/L (median 0.98 mg/L, range <0.2-17.3 mg/L).     

Determination of beta 2-microglobulin in serum by a microparticle-enhanced nephelometric immunoassay.

This fully automated nephelometric immunoassay to quantify beta 2-microglobulin in human serum measures the light-scattering signal produced by agglutination of commercially available latex microparticles (diameter 0.1 micron) coated with specific F(ab')2 against beta 2-microglobulin. The calibration curve, generated by serial dilutions of a beta 2-microglobulin standard of known concentration, is used to calculate beta 2-microglobulin concentrations in serum samples by the logit-log function and linear-regression analysis. The assay range (sample dilution 400-fold) extends from 0.3 to 40.0 mg/L. No antigen excess appears at beta 2-microglobulin concentrations up to 320 mg/L. Within-run CVs ranged from 1.0% to 3.4%, and between-days from 1.2% to 2.8%. Total imprecision (CV) was < 5%. Analytical recovery averaged 99.5% +/- 2.8%. Rheumatoid factor, complement, bilirubin (up to 340 mumol/L), and hemoglobin (up to 2.0 g/L) do not interfere. Strongly turbid lipemic samples must be cleared before analysis. Standard curve linearity was very good in samples covering the clinical useful range of concentrations. Results of the method correlated well with those of radioimmunoassay and microparticle enzyme-linked immunoassay (r = 0.979 and 0.975, respectively). The reference interval (nonparametric estimation) in apparently healthy adults (n = 303) was 0.87 (0.80-0.94) to 2.42 (2.28-2.45) mg/L; the median value was 1.54 mg/L.     

Fully automated immunoassay for quantitative determination of FXIII

Coagulation factor XIII (FXIII) is essential for clot stabilization. Deficiency of FXIII is associated with a risk of bleeding and impaired wound healing. Substitution therapy with FXIII remedies for patients with low plasma levels of FXIII requires diagnostic quantification of the factor before and during therapy. Here, we describe a prototype of a preliminary research immunoassay for quantification of FXIII antigen on automated coagulation instruments. The prototype assay is based on a monoclonal antibody (mAb) directed against FXIII A chain, whereas the mAbs are coupled to latex particles. FXIII in a plasma specimen causes agglutination of the latex particles, which can be quantified turbidimetrically. Performance data of the assay prototype processed on BCS? XP and Sysmex? CA-1500 instruments demonstrate a good correlation to the Berichrom? factor XIII activity assay1 from Siemens Healthcare Diagnostics (r = 0.94). Results: Comparability of instruments was excellent (r = 0.98). Coefficients of variation of total imprecision measurements ranged from 2.2 to 3.4%. Linearity was excellent over the range tested (12-121% FXIII). Analytical sensitivity was 0.51% FXIII on BCS XP and 0.44% FXIII on Sysmex CA-1500, respectively. No interference (>10% bias) was observed with haemoglobin (up to 400 mg/dl), cholesterol (up to 300 mg/dl), bilirubin (up to 60 mg/dl) or triglycerides (up to 3000 mg/dl). Conclusion: The preliminary research assay prototype has the potential for excellent analytical sensitivity, precision, and dynamic range suitable to measure reliably FXIII antigen levels in human plasma.     

A sol particle homogeneous immunoassay for measuring serum cystatin C

OBJECTIVES: We have developed a sol particle immunoassay (SPIA) for measuring serum cystatin C, an endogenous marker of glomerular filtration rate (GFR). DESIGN AND METHODS: We used colloidal gold particles coated with anti-cystatin C antibodies. RESULTS: The assay was linear in the range 0.2 to 8 mg/L and showed good correlation between theoretical and obtained values. The within and between-day coefficients of variation (CV) varied from 1.1 to 1.6% and 0.4 to 1.0%, respectively. Analytical recovery was 95.7 to 103.7%. No interference could be detected from bilirubin (up to 200 mg/L), hemoglobin (up to 3 g/L), chyle (up to 5,000 FTU), rheumatoid factor (up to 1,000 IU/mL) or anticoagulants. Serum samples (n = 101), from which turbidity had been removed, were measured either with our assay or with Dako Cystatin C PET kits, using a Model 7070 Hitachi automatic clinical analyzer. Comparing these two methods, the calculated linear regression equation and the correlation coefficient were y = 0.986 x -0.153 and r = 0.995, respectively. CONCLUSIONS: Our new SPIA assay is a fully automated, homogeneous immunoassay that can readily be used in conjunction with various commercial analyzers that are currently available. The assay is sensitive, precise and suitable for clinical use and appears to offer advantages over other GFR markers such as creatinine.     

Quantitative nephelometric assay for determining myoglobin evaluated

A recently introduced automated nephelometric immunoassay involving shell/core particles for determination of myoglobin (Behringwerke) was evaluated with the BNA Nephelometer. Method precision was good: the intra-assay CV varied between 1.5% and 6.1%; with daily calibration, the interassay CV ranged between 1.5% and 7.5%. For usual sample dilutions, the assay response varied linearly with myoglobin concentrations up to 23.1 nmol/L. After automatic dilution by the instrument, concentrations up to 2310 nmol/L could be measured without high-dose "hook" effect. Further manual dilution allowed measurement of myoglobin concentrations up to 26,000 nmol/L. Calibration was stable for at least seven days. We detected no significant interferences from hemoglobin, haptoglobin, bilirubin, iodine-containing contrast media, and rheumatoid factors. Treating lipemic samples with Lipoclean (Behringwerke) decreased test results. Simultaneously drawn serum and plasma samples from the same subject showed no consistent differences in myoglobin concentrations. The mean reference myoglobin concentration was 1.380 (SD 0.82) nmol/L for men and 0.878 (SD 0.45) nmol/L for women. In patients with renal insufficiency, serum creatinine values were moderately related to serum myoglobin values (r = 0.465). Although a commercial radioimmunoassay (Byk-Sangtec) and the nephelometric assay intercorrelated well (r = 0.929), values obtained by nephelometry were significantly lower (P less than 0.05). By both assays, results for heart and skeletal muscle tissue extracts showed no correlation, a finding that suggests the existence of multiple forms of myoglobin in human tissues. We conclude that immunonephelometry is a rapid, practical, and reliable method for measuring myoglobin in serum.     

Detection of anti-laminin antibodies in sera by latex agglutination

We describe a latex particle agglutination assay for detecting circulating antibodies against laminin, a noncollagenous glycoprotein of basement membranes. Polystyrene latex particles on which laminin has been adsorbed are incubated with serum for about 25 min at 42-45 degrees C. The agglutination is then measured by counting residual unagglutinated particles. Polyethylene glycol 6000 enhances the agglutination. The assay is fully automated, yielding results in about 45 min, for 50 samples per hour. Addition of purified laminin abolishes the agglutination of laminin-coated particles in practically all positive sera. The anti-laminin antibody titers obtained by this latex immunoassay and by radioimmunoassay correlated well in 161 sera from patients with suspected or established renal diseases. The agglutination assay more frequently gave positive results for cases of glomerulonephritis with linear deposits (20/22 cases) than for glomerulonephritis with granular deposits (7/68) or glomerulonephritis with no glomerular deposits (2/13). The finding of low anti-laminin antibody titers in sera from about 15% (34/230) of the healthy subjects suggests that these autoantibodies are pathogenic only in certain circumstances.     

Microparticle-enhanced nephelometric immunoassay of lactoferrin in human milk

A microparticle-enhanced nephelometric immunoassay was developed for lactoferrin quantitation in human milk. It is based on the nephelometric measurement of the light scattered during the competitive immunoagglutination of a microparticle-lactoferrin conjugate with an antilactoferrin antiserum. This immunoassay is sensitive (detection limit in reaction mixture, 0.2 mg/L) and can be performed in diluted milk (1/3,000 in reaction mixture), excluding any interference or sample pretreatment. It allowed the quantification of lactoferrin on a large range of concentrations (0.675–21.6 g/L) with accuracy (linear recovery in dilution-overloading assay) and precision (within- and between-run coefficients of variation from 3% to 6%). Changes in the lactoferrin concentration of human milk during lactation were determined in 190 samples. The concentration and ratio of lactoferrin vs. total protein were found to be significantly higher in colostrum (5.9 g/l, 29%) than in transitional milk (2.9 g/L, 22%) or mature milk (2.5 g/L, 24%). J. Clin. Lab. Anal. 11:239–243, 1997. © 1997 Wiley-Liss, Inc.     

7种半胱氨酸蛋白酶抑制剂C检测系统的分析性能评价

目的评估7种半胱氨酸蛋白酶抑制剂C（CysC）检测系统的分析性能。方法应用美国临床实验室标准化协会（CLSI）系列文件评估5个颗粒增强免疫透射比浊（PETIA）检测系统和1个均相溶胶颗粒免疫法（SPIA）检测系统的精密度、正确度、空白限（LoB）、抗干扰性以及与SIEMENSBNⅡ颗粒增强免疫散射比浊（PE—NIA）检测系统（简称BNⅡ系统）的相关性和偏差。结果6个检测系统（以A—F表示）和BN1I系统在CysC浓度为0．8～5．0mg／L时的总批内变异系数（CV）均〈3．75％,总批间CV除E系统外均〈5％;正确度验证显示A—E系统和BNⅡ系统测定ERM—DA471的绝对偏倚分别为0．00、0．00、1．01、-0．01、-0．50和-0．35mg／L,相对偏倚分别为0％、0％、18．43％、-0．18％、-9．12％和-6．39％;测定CAP室间质评物显示仅D系统和BN1I系统较为理想。A～F系统及BNⅡ系统的LoB分别为0．00、0．00、0．31、0．01、0．10、0．06和〈0．05mg／L。干扰分析显示Hb≤13g／L、TG≤28mmol／L时,对A、B系统及BNⅡ系统无明显影响（干扰〈±10％）,其他系统均有不同程度干扰。相关分析显示A～F系统与BN1I系统相关性较好[相关系数（r）均〉0．975,P〈0．01]。偏差分析显示,A～F系统与BNII系统的平均偏差分别为－0．02、－0．10、－0．31、0．05、0．04、0．36mg／L。结论CysC各检测系统测定有证参考物质ERM—DA471的最大偏倚可达到lmg／L,最大相对偏倚为18．43％;其中PENIA在测定ERM—DA471和CAP室间质评物时结果低于PETIA;部分检测系统分析性能存在不足。     

Measurement of faecal immunoglobulin a levels in young children

A nephelometric immunoassay was developed to quantify immunoglobulin A (IgA) in children's stools. This method enables IgA in faecal protein extracts to be measured over a large range of concentrations (1.61-51.50 mg/L) with good accuracy (linear recovery in dilution-overloading assay) and precision (within- and between-run coefficients of variation (CVs) of 1-6%). An excellent recovery (105%) was obtained in stool samples overloaded by purified colostral IgA, demonstrating that the method used for faecal IgA extraction is adapted, not to induce significant IgA degradation, and probably allow a complete extraction of IgA. The amount of faecal IgA, as determined in stool samples from 125 children (6-24 months old), was an average of 14 mg per 100 g of stools (about 10% of the total protein stool content), with large individual variation (3-30 mg per 100 g of stools). No correlation was observed between faecal IgA amounts and the children's age or sex. Such an immunoassay could enable exhaustive noninvasive investigations of the maturation of the intestinal immune system, as well as accurate studies of the effect of oral dietary supplementation on IgA regulation.     

Determination of beta 2-microglobulin in human urine and serum by latex immunoassay

This highly sensitive method for determination of beta 2-microglobulin (beta 2-m) in human urine or serum is based on direct agglutination by beta 2-m of latex particles on which an antibody against beta 2-m is adsorbed. The agglutination is quantified by counting the remaining unagglutinated particles, or by turbidimetry. A novel aspect of this method is the capability to prevent nonspecific agglutination of the antibody-coated particles by diluting them with an albumin solution of well-defined characteristics (pH, freshness, concentration) just before the assay. The assayable concentration range is 1--32 micrograms/L, the detection limit 0.5 micrograms/L. Within-assay CV, based on 10 determinations of beta 2-m in urine and serum at two different dilutions, ranged from 4.6 to 8.7%. Between-assay CV, calculated from 10 determinations of beta 2-m in urine and serum, was 10 and 8.4%, respectively. Analytical recovery of beta 2-m in urine averaged 97% and in serum 104% (n = 10). No component of urine or serum interfered. Coefficients of correlation for beta 2-m in urine or serum as measured by radioimmunoassay and latex immunoassay were 0.97 and 0.93, respectively. Concentrations of beta 2-m in serum and urine from 33 healthy men (ages 20 to 67 years) averaged 1.5 mg/l and 54 micrograms/g of creatine, respectively.     

Examination of a competitive enzyme-linked immunoassay (CELIA) technique and a laser nephelometric immunoassay technique for the measurement of apolipoprotein B

A competitive enzyme-linked immunoassay (CELIA) technique for quantitative measurement of apolipoprotein B (Apo B) was developed. The method is a non-isotopic immunoassay that utilizes a soluble enzyme/antibody complex as a universal labeling reagent. The method was characterized according to precision, sensitivity, recovery and parallelism. The CELIA Apo B method was compared to a commercially available laser nephelometric immunoassay. We found that the nephelometric results were highly correlated with triglyceride levels and the nephelometric assay was susceptible to interference from lipemia or turbidity. The range of values obtained on 56 apparently healthy, fasting young adults was 0.35-1.25 g/l by the CELIA method and 0.40-1.00 g/l by the nephelometric immunoassay. The nephelometric method was more precise (coefficient of variation 5%) than the CELIA technique (CV 10%); however, the CELIA method seems to be less sensitive to interferences.     

Evaluation of Stratus CS stat fluorimetric analyser for measurement of cardiac markers Troponin I (cTnI), creatine kinase MB (CK-MB), and myoglobin.

Myoglobin, CK-MB, and Troponin I (cTnI) are cardiac muscle necrosis markers that are useful for detecting acute myocardial infarction (AMI). The Stratus CS (Dade Behring, Inc.) is a discrete fluorimetric immunoassay analyser designed for the determination of the three cardiac markers from a single sample of whole blood or plasma. Overall analytical performances of the Stratus CS provided by Dade Behring were evaluated according to the French Society of Clinical Biology guidelines. Within-run imprecision (n = 20) for the three parameters at three levels gave values under 5%, whereas CVs for between-run imprecision (n = 20) were under 6%. The sensitivities were 0.03 microg/L for cTnI and 0.4 microg/L for CK-MB. Linearities extended from 0-50 microg/L for cTnI, 0-140 microg/L for CK-MB, and 1-900 microg/L for myoglobin. The results, particularly those obtained on whole-blood samples, correlated well with those obtained on Stratus II. We did not find any interference with haemolysis, icterus, or lipemia. The system was very easy to use, and fulfills the requirements for the analysis of the three cardiac markers in patients with acute chest pain in emergency situations.     

Detection of anti-human T-lymphotropic virus type I antibody in whole blood by a novel counting immunoassay

BACKGROUND: Assays to screen for and confirm the presence of the antibody for human T-lymphotropic virus type I (HTLV-I) are currently performed with serum or plasma. We developed and evaluated a new counting immunoassay (CIA) for the detection of HTLV-I antibody in whole blood, using recombinant and synthetic peptide antigens. METHODS: We assessed the CIA for detection of HTLV-I antibody in whole blood and plasma. The CIA is an immunity-measuring method that combines latex agglutination with particle-counting technology. The numbers of agglutinated latex particles, single latex particles, and blood cells in a sample are measured based on differences in particle size between latex particles and blood cells. RESULTS: The CIA and ELISA methods were in agreement for all 24 plasma samples tested, including those from 6 patients with HTLV-I-associated diseases, 6 HTLV-I carriers, and 12 HTLV-I antibody-negative individuals. The concordance between the ELISA (plasma) and the CIA (whole blood) for samples from 24 patients was 100%. The concordance between a particle agglutination method (plasma) and the CIA (plasma or whole blood) for 1065 patients was 99.5%. The concordance between results obtained for 1065 pairs of plasma and whole blood samples with the CIA method was 100%. HTLV-I antibody in whole blood was stable for 3 days after blood collection. With this CIA method, results were available within 15 min. CONCLUSIONS: The CIA method can be used in screening for HTLV-I. The use of whole blood rather than serum or plasma reduces the sample volume and number of blood collections required, as well as assay time.