Highly sensitive qualitative methods for serum choriogonadotropin (hCG): clinical specificity studies

We screened six highly sensitive kits, designed for serum pregnancy tests, for false-positive results. The two best were then evaluated more extensively. The "BETA-hCG MAIA-clone" (I) and the "TANDEM ICON" (II) kits gave only negative results for 100 sera from men at 5, 10, and 25 int. units/L (1st IRP). Of 100 serum specimens from post-menopausal women three and 10 were hCG positive by the II and the I reagents, respectively, but only at the 5 int. units (1st IRP) of hCG per liter level of sensitivity. At 10 and 25 int. units/L, all specimens were negative by both tests. The manufacturers of these kits recommend pregnancy testing only at the 25 int. units/L level of analytical sensitivity. By quantitative methods, hCG concentrations in the II positive samples ranged from 6 to 20 int. units/L (1st IRP) and lutropin concentrations were between 130 to greater than 150 int. units/L. The medical records of the corresponding patients did not support the presence of trophoblast or any other hCG-secreting tissues. During 15 months of routine use of the II reagents at an analytical sensitivity of 25 int. units/L (1st IRP) hCG for pregnancy testing (greater than 4000 serum specimens from pre-menopausal women), the staff has not reported to us any suspected false-positive findings.     

An evaluation of six solid-phase thyrotropin (TSH) kits

This article describes an objective evaluation of six thyrotropin (TSH) kits. One was a radioimmunoassay kit taken for comparison, three were immunoradiometric assays and one was an immunoenzymometric assay. The laboratory internal immunoluminometric assay for thyrotropin was used to measure the concentrations of thyrotropin in the kit standards using a standard curve of WHO 68/38 international reference preparation in serum from a thyrotoxic patient as matrix. The in-house assay was used to demonstrate the "sensitivity" to citrated plasma and the fact that kit standards could only measure "correctly" when used in its own kit. The study was carried out in a "blind" way, the assayist and organiser not knowing from which of the four groups under test (blood donors - serum and citrated plasma, thyroliberin-test and thyroid outpatient clinic patients) the samples came until the study had been completed. The immunometric assay kits were able to differentiate statistically between euthyroid and untreated hyperthyroid patients, although one IRMA kit (Kit F) had a large "grey zone" where both euthyroid and hyperthyroid patients overlapped. Compound precision profiles covering the range 0-5 mU/l thyrotropin were good, a mean coefficient of variation under 5% within the range 0.5-5 mU/l being demonstrated by 3 immunometric assays. The immunometric assay kit with the most cumbersome methodology showed, as was to be expected, the worst precision. The euthyroid ranges for thyrotropin were similar in 3 immunometric assay kits using the WHO 68/38 reference material as calibrator (Kits C and E, 0.25-3 mU/l) and correlated well with one kit using the 2nd IRP (NIBSC 80/558) as calibration material (Kit D 0.33-4 mU/l), although the results were around 30% higher in Kit D. The second kit (Kit A) using the 2nd IRP material as calibrator gave identical values with the kits using the WHO 68/38 reference thyrotropin-preparation for calibration purposes. In a further kit (Kit F) it was stated that both thyrotropin international reference preparations gave rise to identical serum values when used as calibrators. The thyroliberin-test may have an additional role to play in monitoring returning pituitary function in thyrotoxic patients under treatment as the immunometric assay kits were easily able to measure a thyrotropin difference of 0.5 mU/l in the range 0-1 mU/l. The conventional radioimmunoassay (Kit B) was unable to match the precision and sensitivity of the better immunometric assay kits in the range under 1 mU/1.(ABSTRACT TRUNCATED AT 400 WORDS)     

Multicenter evaluation of new enzyme-linked immunoassays of follitropin and lutropin in serum or plasma

Results from a multicenter evaluation of two new enzyme-linked immunosorbent assays [Enzymun-Test for follitropin (FSH) and lutropin (LH)] are presented and compared with results from 11 other commercial immunoassays, radioactive as well as nonradioactive. Enzymun-Test FSH and LH assays are suitable for automated systems and manual applications. The tests were reproducible (CV less than 5%), highly specific, and sensitive enough (less than 0.5 int. unit/L) to measure the hormones directly in almost all patients' samples, except for LH measurements in prepubertal children. We did not find interference by heterophilic antibodies or other factors. A comparison of assays for FSH found very good agreement among all modern two-site assays; competitive immunoassays almost invariably yielded systematically lower results for FSH, probably because of the heterogeneity of the International Reference Preparation (2nd IRP FSH, 78/549). For LH also we found good agreement, with no systematic differences among the various reagents. Guidelines for reference values with the new reagents are given.     

Minimizing between-kit variability in immunoassay for carcinoembryonic antigen by use of a common standard

Between-laboratory agreement of CEA determinations collected in a multicenter study has been substantially improved (CV decreased from 60.4 to 21.6%) by converting the results from mass concentration units (ng/mL) of local kit standards to int. units/L of the international standard first IRP 73/601. Conversion factors for the kits most used were computed, during the same survey, from results of two analytical-recovery experiments in which control samples, supplemented with the international standard, were analyzed by participating laboratories (n = 96).     

Polycystic ovary syndrome: it is always bilateral?

OBJECTIVE: To evaluate whether patients with unilateral polycystic ovary showed different ovarian and uterine blood flow from those with bilateral polycystic ovaries, and to investigate whether there was a correlation between the ultrasonographic aspect and different hormonal parameters. DESIGN: An observational study. SUBJECTS: Sixteen patients with unilateral polycystic ovary and twenty patients with bilateral polycystic ovaries underwent clinical, biochemical, gray-scale and color Doppler ultrasonographic evaluation. METHODS: The following parameters were evaluated: hormonal (luteinizing hormone (LH), follicle stimulating hormone (FSH), LH/FSH concentration ratio, estradiol, prolactin, androstenedione, testosterone), clinical (body mass index, Ferriman-Gallwey score), ultrasonographic (ovarian volume, number and distribution of subcapsular follicles, stromal score) and Doppler (uterine artery and intraparenchymal vessel pulsatility index, ovarian stromal vascularization), in oligomenorrheic patients in the early follicular phase (cycle days 3-5) or in amenorrheic patients at random. RESULTS: Significantly higher androstenedione plasma levels and LH/FSH concentration ratios were observed in bilateral polycystic ovaries. In unilateral polycystic ovaries, gray-scale and color Doppler ultrasonography showed different features in the affected and the unaffected ovary, similar to the appearance of a polycystic and normal ovary, respectively. CONCLUSION: Polycystic ovary syndrome does not predetermine a single ultrasonographic and Doppler pattern.     

Evaluation of four commercially available assays for free thyroxin

We assessed two two-step and two analog assays for measuring free thyroxin (FT4) in serum: Clinical Assays' "GammaCoat Free/Total T4" (CA), Vitek's "KinetiCount Phase II Free T4" (VTK), Diagnostic Products Corporation's "Coat-a-Count Free T4" (DPC) kit (June 1987 version), and Amersham's "Amerlex-M Free T4" (AMX). The VTK assay is automated except for the initial pipetting step. Interassay results correlated well except for samples with abnormal serum albumin concentrations. FT4 values for hypoalbuminemic samples showed a highly significant (P less than 0.0001) correlation with serum albumin concentration in the DPC and AMX assays. The relationships are described by the equations y = 0.382albumin (g/L) + 0.81 pmol/L and y = 0.450albumin (g/L) - 3.20 pmol/L, respectively. When we used an equation derived from the Law of Mass Action to adjust FT4 values to values expected at an ideal albumin concentration, the observed correlation of albumin and FT4 was abolished completely in the DPC assay, and partly so in the AMX assay. The precision of CA was comparable with that of the analog assays; the CV for the VTK assay was approximately twice that for the other three assays.     

卵巢超声特征联合内分泌指标在不同类型多囊卵巢综合征应用价值分析

目的研究卵巢超声特征联合内分泌指标在胰岛素抵抗型与非胰岛素抵抗型多囊卵巢综合征中的应用价值。方法选取2013年2月—2015年3月于本院就诊的共218例多囊卵巢综合征患者作为研究对象。采用HOMA-IR标准进行分组,HOMA-IR≥2.69的115例为胰岛素抵抗组;HOMA-IR2.69的103例者为非胰岛素抵抗组。同时选取同期进行健康体检者69例作为对照组。检测卵巢超声特征,包括卵巢包膜厚度、卵巢直径、卵泡最大直径、OV、卵泡体积、卵泡数、血流指数。检测内分泌指标,包括FSH、LH、LH/FSH、E2、T、PRL、FINs、FPG、SHBG。结果胰岛素抵抗组和非胰岛素抵抗组卵巢包膜厚度、OV、卵巢直径、卵泡体积、卵泡数、血流指数大于对照组,卵泡最大直径小于对照组,且差异均有统计学意义(P0.05);胰岛素抵抗组的OV、卵巢直径、卵泡体积、卵泡数目、血流指数大于非胰岛素抵抗组,卵泡最大直径小于非胰岛素抵抗组,且差异均有统计学意义(P0.05);胰岛素抵抗组和非胰岛素抵抗组LH、LH/FSH、FSH、FINs及T大于对照组,SHBG、E2小于对照组,且差异均有统计学意义(P0.05);胰岛素抵抗组的FPG大于对照组,且差异具有统计学意义(P0.05);胰岛素抵抗组的T、FINs大于非胰岛素抵抗组,胰岛素抵抗组SHBG小于非胰岛素抵抗组,且差异有统计学意义(P0.05)。单因素相关性分析显示,OV与LH/FSH、T、BMI、HOMA-IR呈正相关(r=0.255,0.267,0.534,0.427,P0.05),卵泡最大直径约T、HOMA-IR、BMI呈负相关(r=-0.426,-0.433,-0.317,P0.05)。卵泡刺激素与卵泡数呈正相关(r=0.817,P0.05)。结论胰岛素抵抗型多囊卵巢综合征患者卵泡最大直径减小,OV增大。OV与LH/FSH、T、BMI、HOMA-IR呈正相关,卵泡最大直径约T、HOMA-IR、BMI呈负相关。卵泡刺激素与卵泡数呈正相关。     

Follicle-Stimulating Hormone (FSH) and Luteinizing Hormone (LH) in the Urine of Prepubertal Children

Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) have been measured by specific bioassays in pooled urine samples from prepubertal children, aged 2-6 yr, and from male adults. For children the mean urinary excretion of FSH was 2.2 U 2nd International Reference Preparation (2nd IRP) per liter and the mean urinary excretion of LH was 0.44 U 2nd IRP per liter. For adults the mean FSH excretion was 5.6 U 2nd IRP per liter and the mean LH excretion was 4.7 U 2nd IRP per liter. Our data show a 2.5-fold increase of FSH, a 10.7-fold increase of LH, and a consequent decrease in the FSH: LH ratio from 5 to 1 between childhood and adulthood. FSH and LH in urine from three patients with gonadal abnormalities have also been studied. The results from normal children, adults, and abnormal patients form a spectrum and reveal that sexual maturity is accompanied by a marked increase in the excretion of LH with relatively smaller increases in FSH.     

Serum human chorionic gonadotrophin levels in early pregnancy

Serum hCG reference intervals for various gestational periods in normal pregnancies were determined using three commercial assays--two standardized against the WHO 2nd IS (Amersham Amerlex-M beta HCG RIA (AMX) and Abbott beta-HCG 15/15 (ABB] and one standardized against the WHO 1 IRP (Hybritech Tandem -E HCG (HYB]. Serial samples from patients with accurately determined gestational periods were analyzed. We correlated these assays to determine the validity of the common practice of interchanging values between assays using the same WHO standard and of converting 1st IRP values to 2nd IS values by a fixed factor. The slope of correlation between the two 2nd IS assays (AMX, ABB) was 1.43, r = 0.960; whereas between the 1 IRP assay (HYB) and the two 2nd IS assays the slopes were 1.67, r = 0.963 and 1.22, r = 0.971 for AMX and ABB, respectively. In a prospective study of 52 patients with normal pregnancies, serum beta-hCG values in 46% of samples taken at 28-35 days gestation fell below the lower limit of the reference curves supplied with the AMX kit. Ninety-two percent of samples were within the newly established intervals. These results indicate that supplier's reference limits may not be accurate; in addition, a common factor should not be used to convert values from one commercial kit to another.     

In vitro and in vivo effects of increased concentrations of free fatty acids on free thyroxin measurements as determined by five assays

To compare in vitro and in vivo effects of increased concentrations of free fatty acids (FFA) on free thyroxin (FT4) values, we measured FT4 in three pooled sera supplemented with oleate and in serum from 18 euthyroid patients before and after an infusion of fat emulsion (Intralipid). We used five FT4 RIA kits: two two-step methods [Gammacoat, Baxter (GC); Ria-gnost, Behring (RG)], two analog RIAs [Amerlex-M, Amersham (AM); Coat-Ria, BioMérieux (CR)], and one kit with labeled antibodies [Amerlex-MAB*, Amersham (AA)]. In vitro, at the maximum oleate addition of 5 mmol/L, FT4 increased when measured by the GC and RG kits, decreased by the AM kit, and showed no significant change by the CR and AA kits. In vivo, post-Intralipid, FFA concentrations rose significantly and the FT4 changes agreed with the results of the in vitro experiments, except for the RG kit, for which FT4 increased in only nine patients. We conclude that in vitro oleate addition is useful to predict the in vivo effect of increased FFA on FT4 values; moreover, in serum from euthyroid subjects with high concentrations of FFA, FT4 analyzed with the CR or AA kits should better agree with normal results for thyrotropin than FT4 values measured with the other kits.     

Solving the problem of antibody interference in commercial "sandwich"-type immunoassays of carcinoembryonic antigen

We evaluated the effect of human anti-murine antibodies (HAMA) on apparent concentrations of carcinoembryonic antigen (CEA) as measured in serum with commercial enzyme immunoassay (EIA) kits manufactured by Abbot ("two-step" double monoclonal antibody assay), Roche, and Hybritech (room-temperature protocol). In sera from patients given parenteral murine monoclonal antibody for experimental diagnostic and immunotherapy studies, HAMA titers were determined with Immunomedics' "ImmuSTRIP HAMA-EIA" kit reagents. "True" CEA titers were established by using the ImmuCEA/MA-EIA and heat-extraction to destroy HAMA before assay for CEA. The concordance of the ImmuCEA/MA assay with the Abbott and Roche CEA EIAs was established with sera from normal individuals and from patients who had not received parenteral injections of murine monoclonal antibody. At high (100 mg/L) concentrations of HAMA, false-positive results were observed with all three kits. The Hybritech and Roche assays were more sensitive to interference by HAMA than was the Abbott CEA-EIA, false-positive results being observed at HAMA concentrations between 1 and 10 mg/L. Similar sensitivity of the three kits to interference by primate anti-MAb sera was demonstrated. Use of primate anti-MAb sera to create controls with HAMA activity and of analyte is recommended to evaluate MAb assays for potential HAMA interference and for use to devise methods to eliminate HAMA interference.     

曲普瑞林兴奋试验评价多囊卵巢综合征患者性腺轴功能

  目的  利用促性腺激素释放激素类似物(曲普瑞林)兴奋试验评价多囊卵巢综合征(polycystic ovary syndrome, PCOS)患者的下丘脑-垂体-性腺轴功能并探讨其变化特点。  方法  对PCOS患者(n=20)和健康对照者(n=30)进行曲普瑞林兴奋试验, 在0、15、30、45、60和90 min测定血黄体生成素(luteinizing hormone, LH)和卵泡刺激素(follicular stimulating hormone, FSH)的水平。比较PCOS组和健康对照组在基线状态以及兴奋试验后LH、FSH水平的变化以及LH/FSH比值的差异。  结果  对照组和PCOS组患者的睾酮分别为(1.9±0.5)nmol/L和(3.5±1.4)nmol/L(P=0.012)。PCOS患者的基线LH水平高于对照组[(11.3±6.6)U/L比(3.7±2.7)U/L, P=0.028];在曲普瑞林兴奋试验中, PCOS组LH的升高幅度明显大于对照组; 在第15分钟, PCOS组和对照组的LH分别为(41.4±28.0)和(24.7±19.0)U/L(P=0.036);在第60分钟, PCOS组和对照组的LH分别为(64.0±34.8)和(44.8±22.5)U/L(P=0.060)。PCOS组和对照组的基线FSH水平分别为(4.6±2.0)和(4.9±1.6)U/L(P=0.467);在曲普瑞林兴奋试验中, PCOS组FSH水平升高幅度小于对照组; 在第60分钟, 两组FSH水平分别为(9.9±4.0)和(17.3±5.6)U/L(P=0.041)。基线状态PCOS组和对照组的LH/FSH比值分别为2.9±1.1和0.8±0.2(P=0.023);此比值在曲普瑞林兴奋试验中进一步升高, 在第60分钟时两组分别为6.5±1.3和3.1±0.9(P=0.038)。  结论  PCOS患者基础状态LH和LH/FSH比值明显升高, 在曲普瑞林兴奋试验中, LH和FSH曲线之间的差距进一步增加, LH/FSH比值进一步升高, 提示PCOS患者存在特征性的下丘脑-垂体-卵巢轴功能异常。     

多囊卵巢综合征卵巢穿刺内凝术后子宫卵巢动脉血流与激素变化的研究

目的　探讨多囊卵巢综合征 (PCOS)患者经腹腔镜卵巢穿刺内凝术 (LOPE)前后子宫和卵巢动脉血流参数的变化及与激素变化的相关关系。方法　采用经阴道彩色血流显像 (TV CDFI)对 2 8例PCOS患者手术前后的子宫、卵巢动脉进行检测并测定激素水平。结果　PCOS患者手术后 ,两侧卵巢血流阻力指数 (RI)、雄激素、LH FSH显著降低 (P <0 .0 1) ,出现优势卵泡右侧子宫动脉RI降低 (P <0 .0 5 )。回归分析子宫动脉PI与LH FSH相关 (P <0 .0 5 ) ,LH FSH与雌激素相关 (P <0 .0 1)。结论　LOPE术后可显著改善卵巢的微循环及增加优势卵泡侧的子宫动脉的血流灌注 ,LH FSH可能在调节子宫动脉的血流灌注及雌激素方面具有一定的作用。     

The efficacy of Tung’s acupuncture for sex hormones in polycystic ovary syndrome: A randomized controlled trial

BackgroundPolycystic ovary syndrome (PCOS) is a common and heterogeneous endocrine disorder in reproductive-age women. Tung's acupuncture, a Traditional Chinese Medicine (TCM) treatment, is widely used for PCOS in East Asia, but evidence on its efficacy is rare. The aim of this RCT study was to examine whether the Tung’s acupuncture could be a complementary treatment method for PCOS.MethodsA total of 60 PCOS patients were randomly assigned to a Tung's acupuncture group (n = 30) or a cyproterone acetate/ethinylestradiol (CPA/EE) group (n = 30). Each participant received treatments for 12 weeks to assess the short-term treatment efficacy and then followed up for another 12 weeks to assess the long-term treatment efficacy. The primary outcome examined was change in the ratio of luteinizing hormone (LH) to follicle-stimulating hormone (FSH); the secondary outcomes examined were changes in body mass index (BMI), LH, FSH, total testosterone (TT), ovarian volume, polycystic ovary number and menstrual frequency.ResultsBoth groups showed significant reductions in the LH/FSH ratio, LH and TT after 12-week treatment (p < 0.001) and 12-week follow-up (p < 0.05). No significant differences existed between the two groups (p > 0.05). Both groups showed significant improvement in BMI, menstrual frequency and polycystic ovary number after 12-week treatment (p < 0.05).ConclusionCompared with CPA/EE, Tung’s acupuncture showed no better improvement on LH/FSH ratio for PCOS although it could reduce the ratio. Tung's acupuncture might have some effect on long-term weight control and menstruation frequency. Further studies addressing this study’s limitations are recommended.     

二甲双胍对多囊卵巢综合征患者内分泌功能的影响

目的探讨二甲双胍对多囊卵巢综合征(PCOS)合并胰岛素抵抗(IR)患者内分泌的影响。方法 P-COS合并IR患者50例于自然月经或撤退性出血第2天开始服用二甲双胍12周,观察治疗前后血清促卵泡生成素(FSH)、黄体生成素(LH)、睾酮、雌二醇、雄烯二酮、性激素结合蛋白(SHBG)浓度、胰岛素(INS)水平以及血糖的变化。结果治疗后患者各时相INS水平显著下降,差异有统计学意义(P<0.01);患者血清LH、LH/FSH比值、睾酮和雄烯二酮水平均显著下降,差异有统计学意义(P<0.01);SHBG水平显著升高,差异也有统计学意义(P<0.01)。结论二甲双胍通过改善IR降低INS水平,改善患者临床症状和内分泌指标,使PCOS患者异常的血激素相得到明显改善。     

中西医结合治疗胰岛素抵抗型PCOS不孕的效果

目的探讨中西医结合治疗胰岛素抵抗型多囊卵巢综合征（PCOS）不孕的临床效果。方法将60例胰岛素抵抗型PCOS不孕病人随机分为A、B两组,各30例。A组以中药调经颗粒配合西药氯米芬（CC）、二甲双胍治疗;B组单纯应用CC、二甲双胍治疗。两组各治疗3个月,观察临床疗效及治疗前后血清空腹胰岛素（INS）、卵泡刺激素（FSH）、黄体生成素（LH）、LH/FSH、睾酮（T）水平。结果 A组疗效明显优于B组（uc=1.99,P〈0.05）。A、B两组治疗后血清INS、LH、T水平及LH/FSH较治疗前显著降低（t=2.23-13.86,P〈0.05、0.01）。A组治疗后血清INS、LH、T水平及LH/FSH下降较B组明显（t=2.59-3.86,P〈0.05）。A组副作用发生率低于B组（χ2=13.61,P〈0.01）。结论中西医结合治疗胰岛素抵抗型PCOS不孕的临床效果优于单用西药疗法,中医中药在该病治疗过程中发挥了独特的优势。     

Parathyrin assay. An analytical evaluation of two commercial Immuno Radiometric Assay kits

We have performed a comparative evaluation of two Immuno Radiometric Assay (IRMA) kits for parathyrin against an existing Radioimmuno Assay (RIA) technique for the measurement of intact parathyrin. The analytical evaluation which was performed in line with the ECCLS recommended kit evaluation protocol showed a marginal improvement in precision with the new assays. There was a substantial improvement in the theoretical limit of detection utilising the IRMA kits although it may prove difficult to realize this improvement in practice with individual samples because of differing protein matrices. The evaluation also demonstrated the degree of parallelism and range of linearity of both kits as well as inaccuracies when compared with the International Reference Preparation for parathyrin (IRP 79/500) as the accepted standard. The demonstration of lack of agreement between measured and kit assigned results for standards when cross-over studies between kits were performed may highlight a possible contributing factor to inaccuracy. Alternatively there may be a difference of antisera avidity within the kits for intact parathyrin. Whilst minor differences in sample stability were demonstrated between the kits, the sample stability was much improved compared to that for intact parathyrin measurement by RIA. The correlation studies showed a degree of correlation consistent with other comparisons similarly performed.     

Evaluation of the Hybritech Photon Analyzer and of an improved procedure for choriogonadotropin in serum

We evaluated the Hybritech Photon Analyzer for its applicability to enzyme immunoassays. This instrument measures absorbances only at 405, 450, and 490 nm. Photometric linearity was good at all three wavelengths. However, the true absorbance range at these wavelengths was 0-1.6 A instead of 0-2.0 A as specified by the manufacturer. We also evaluated the Hybritech "Tandem-E" method for quantifying choriogonadotropin (hCG) in serum. A modification of the recommended procedure improved the precision of the assay. The detection limit of the modified procedure, 1 int. unit/L, permits reliable assays of hCG at concentrations near the upper limit of normal (3 int. units/L). Results by both procedures varied linearly with hCG concentrations up to 250 int. units/L. The Photon Analyzer eliminates the need for manual calculations. Quantitative results agree within +/- 1% with those measured in the "Stasar III" spectrophotometer.     

Chemically blocked analog assays for free thyronines. I. The effect of chemical blockers on T4 analog and T4 binding by albumin and by thyroxin-binding globulin

Analog assays for free thyroxin (FT4) produce inaccurate results because the T4 analog is sequestered by albumin. Diagnostic Products Corp. (DPC) introduced the concept of chemically blocking analog-albumin binding in 1982. While DPC succeeded in eliminating albumin dependence, their 1985 version of chemically blocked FT4 assay appeared to be "thyroxin-binding globulin" (TBG) dependent, producing inappropriately low FT4 results with low TBG concentrations and high results with high TBG concentrations. We examined the effects of chemical blockers on albumin and TBG binding, using equilibrium dialysis to measure free fractions of T4 analog and T4. We then created FT4 assays in which various concentrations of chemical blockers were used to demonstrate their effects on FT4 estimates in patients with low or increased TBG concentrations or who were pregnant. We found that chemical blockers do displace T4 analog from albumin, but also displace T4 from albumin and, in high concentrations, from TBG as well. It is this displacement of T4 from TBG by chemical blockers that resulted in "TBG dependence" of DPC FT4 estimates. This problem has been corrected in currently available versions of the DPC FT4 kit.