Current status and performance goals for serum thyrotropin (TSH) assays

Current medical needs dictate that laboratories offer thyrotropin (TSH) assays that can reliably measure low TSH concentrations--a prerequisite for using the more cost-effective TSH-centered strategy currently recommended by the American Thyroid Association. This study reviews the functional performance of the TSH immunometric assay methods currently used in clinical practice. Methodological differences between methods, the rationale for using the 20% interassay CV as the functional sensitivity limit for patient reports, and both TSH-related and non-TSH-related specificity problems are reviewed. We recommend that manufacturers and clinical laboratories use a clinically relevant standard protocol for functional sensitivity assessments. In this protocol, human serum pools are analyzed in random order 10 or more times across a clinically realistic time span (which approximates to 6-8 weeks for TSH measurements used in an outpatient setting). Laboratories should independently establish and periodically check their functional sensitivity by the standard protocol and enlist the manufacturer's help to accomplish this if necessary. Manufacturers should (a) develop promotional material that realistically projects the assay's functional sensitivity expected in a clinical laboratory setting, (b) ensure that new clinical laboratory users achieve the projected functional sensitivity target when using the standard protocol, and (c) focus on the typical functional sensitivity obtained by clinical laboratory users rather than the assay's "generation" achieved under ideal conditions. If manufacturers and laboratories collaborate to solve the sensitivity and specificity problems discussed here, clinical laboratories should be better able to consistently deliver reliable serum TSH measurements across the full range of TSH concentrations encountered in clinical practice.

Current status and performance goals for serum thyrotropin (TSH) assays

Current medical needs dictate that laboratories offer thyrotropin (TSH) assays that can reliably measure low TSH concentrations--a prerequisite for using the more cost-effective TSH-centered strategy currently recommended by the American Thyroid Association. This study reviews the functional performance of the TSH immunometric assay methods currently used in clinical practice. Methodological differences between methods, the rationale for using the 20% interassay CV as the functional sensitivity limit for patient reports, and both TSH-related and non-TSH-related specificity problems are reviewed. We recommend that manufacturers and clinical laboratories use a clinically relevant standard protocol for functional sensitivity assessments. In this protocol, human serum pools are analyzed in random order 10 or more times across a clinically realistic time span (which approximates to 6-8 weeks for TSH measurements used in an outpatient setting). Laboratories should independently establish and periodically check their functional sensitivity by the standard protocol and enlist the manufacturer's help to accomplish this if necessary. Manufacturers should (a) develop promotional material that realistically projects the assay's functional sensitivity expected in a clinical laboratory setting, (b) ensure that new clinical laboratory users achieve the projected functional sensitivity target when using the standard protocol, and (c) focus on the typical functional sensitivity obtained by clinical laboratory users rather than the assay's "generation" achieved under ideal conditions. If manufacturers and laboratories collaborate to solve the sensitivity and specificity problems discussed here, clinical laboratories should be better able to consistently deliver reliable serum TSH measurements across the full range of TSH concentrations encountered in clinical practice.

Current status and performance goals for serum thyroglobulin assays

Serum thyroglobulin (Tg) measurements are used as a tumor marker for monitoring patients with differentiated thyroid carcinoma. The clinical utility of six different Tg methods [RIA or immunometric assay (IMA)] currently used in Europe and the US was evaluated, with focus on methodologic standardization, sensitivity, interassay precision across the typical clinical monitoring interval (6 to 12 months), "hook" effects (IMA methods), and Tg autoantibody interference. The methods evaluated were: DYNOtest Tg (Henning), OptiQuant Tg (Kronus), SELco Tg (Medipan), Thyroglobulin IRMA (Pasteur), Nichols Chemiluminescent ICMA (Corning Nichols), and an RIA developed by us (USC Endocrine Services Laboratory). The clinical impact of the current methodologic problems on the use of serum Tg measurements is reviewed. Optimal performance goals are recommended for manufacturers developing and laboratories and physicians selecting a serum Tg method to use for serial long-term monitoring of thyroid cancer patients.

Thyroglobulin measurement. Techniques, clinical benefits, and pitfalls

The validity and reliability of serum Tg measurements is central to accurate diagnosis and cost-effective management of patients with differentiated thyroid carcinoma. Serum Tg is one of the most difficult biochemical tests for a laboratory to maintain at a high level of precision and reliability across the long clinical sampling interval typically employed when monitoring this condition. Physicians should be aware that the diagnostic value of serum Tg measurement is method-dependent, and that intermethod differences still approach 30% even after methods have been standardized on the new CBR reference preparation. This dictates that, ideally, serial serum Tg measurements in a patient should always be made in the same laboratory by the same method. Physicians need to consider a number of factors before selecting a laboratory to perform Tg measurements in patients with differentiated thyroid carcinoma. These factors include assay sensitivity, as judged by the discrimination between lower limit of the euthyroid range and the functional sensitivity limit, as well as assay specificity, especially with respect to serum TgAb interference. laboratories should use a sensitive TgAb immunoassay (not hemagglutination) to prescreen sera for TgAb and report the TgAb level if positive. Furthermore, it is the laboratory's responsibility to advise physicians fully about any change in Tg method as well as the direction of TgAb interference expected with that method. When TgAb is present, the serum Tg level should be a measure of the total (free and TgAb-bound) serum Tg level. Typically, IMA methods underestimate the serum total Tg level, especially when serum TSH is suppressed, whereas RIA methods tend to overestimate the serum total Tg level. The interpretation of a serum Tg level in a TgAb-positive patient should be made with caution and with consideration to any changes in TgAb levels. Serial TgAb monitoring of TgAb-positive patients may provide a physician with additional prognostic information on outcome. Precise, reproducible serial serum Tg measurements are critical, especially when patients are judged to have a high risk for recurrence, have tumors that are inefficient serum Tg secretors (as judged from the relationship between the preoperative serum Tg value and tumor mass or the serum Tg response to endogenous TSH stimulation), or have very high serum Tg values requiring dilution. In such patients, the banking of left-over sera (frozen) for concurrent intra-assay remeasurement with a more recent specimen significantly increases the clinical value of the test and facilitates earlier detection of recurrence or progression (see Fig. 2). Differentiated thyroid carcinoma is frequently diagnosed in young patients with decades of life expectancy. After their initial surgical treatment, these patients need life-long monitoring, because late recurrences and death from the disease can occur. The use of high-quality serum Tg measurements can significantly improve the cost-effective management of this disease by identifying low-risk patients in whom periodic radioiodine scans or therapy may be deferred in favor of serial serum Tg monitoring (on L-T4 suppression therapy). With this approach, expensive imaging procedures can be targeted to the minority of patients who are at high risk for recurrence.

Herpes simplex virus immediate-early protein ICP22 is required for viral modification of host RNA polymerase II and establishment of the normal viral transcription program

Infection of cells with herpes simplex virus type 1 (HSV-1) results in a rapid alteration of phosphorylation on the large subunit of cellular RNA polymerase II (RNAP II), most likely on its C-terminal domain (S. A. Rice, M. C. Long, V. Lam, C. A. Spencer, J. Virol. 68:988-1001, 1994). This phosphorylation modification generates a novel form of the large subunit which we have designed IIi. In this study, we examine roles that HSV-1 gene products play in this process. An HSV-1 mutant defective in the immediate-early transcriptional activator protein ICP4 is able to efficiently induce IIi. Viruses having mutations in the genes for the ICP0, ICP6, or ICP27 proteins are also competent for IIi formation. In contrast, 22/n199, an HSV-1 mutant which contains a nonsense mutation in the gene encoding the immediate-early protein ICP22, is significantly deficient in IIi induction. This effect is seen in Vero cells, where 22/n199 grows relatively efficiently, and in human embryonic lung (HEL) cells, where 22/n199 growth in more restricted. RNAP II is recruited into viral replication compartments in 22/n199-infected cells, indicating that altered phosphorylation of RNAP II is not a prerequisite for nuclear relocalization of RNAP II. In addition, we show by nuclear run-on transcription analysis that viral gene transcription is deficient in HEL cells infected with 22/n199. Viral late gene transcription does not occur efficiently, and antisense transcription throughout the genome is diminished compared with that of the wild-type HSV-1 infection. These transcriptional effects cannot be explained by differences in viral DNA replication, since 22/n199 replicates its DNA efficiently in HEL cells. Our results demonstrated that ICP22 is necessary for virus-induced aberrant phosphorylation of RNAP II and for normal patterns of viral gene transcription in certain cell lines.

Interlaboratory/intermethod differences in functional sensitivity of immunometric assays of thyrotropin (TSH) and impact on reliability of measurement of subnormal concentrations of TSH

Clinically relevant interassay precision profiles for thyrotropin (thyroid-stimulating hormone; TSH) were constructed with human serum pools measured over 4-8 weeks by six immunometric assays, in at least two different reagent lots. Functional sensitivities (the concentration at which the interassay CV is < or = 20%) were determined in four to eight clinical laboratories plus the respective manufacturer's laboratory. These studies revealed that the manufacturer's stated functional sensitivity limit is rarely duplicated in clinical practice. Loss of specificity (indicated by artifactually high values) was seen with some methods when used to measure certain unrefrigerated low-TSH sera. Measurement of TSH in four human serum pools (TSH < 0.05-0.25 mIU/L) by 16 different methods (each in at least eight UK or US laboratories) showed that some methods could not reliably distinguish subnormal from normal TSH values. Better pool rankings and fewer misclassifications of low-TSH sera as "normal" were seen with use of assays capable of "third-generation" functional sensitivity (0.01-0.02 mIU/L) than with assays with "second-generation" functional sensitivity (0.1-0.2 mIU/L). Because inter- and intramethod differences in functional sensitivity negatively impact the diagnostic accuracy and cost-effectiveness of a TSH-centered thyroid-testing strategy, laboratories should independently establish an assay's functional sensitivity by a clinically relevant protocol. Moreover, manufacturers should assess functional sensitivity more realistically and improve the robustness of assays to ensure that their performance potential is consistently met in clinical practice.

Interlaboratory/intermethod differences in functional sensitivity of immunometric assays of thyrotropin (TSH) and impact on reliability of measurement of subnormal concentrations of TSH

Clinically relevant interassay precision profiles for thyrotropin (thyroid-stimulating hormone; TSH) were constructed with human serum pools measured over 4-8 weeks by six immunometric assays, in at least two different reagent lots. Functional sensitivities (the concentration at which the interassay CV is < or = 20%) were determined in four to eight clinical laboratories plus the respective manufacturer's laboratory. These studies revealed that the manufacturer's stated functional sensitivity limit is rarely duplicated in clinical practice. Loss of specificity (indicated by artifactually high values) was seen with some methods when used to measure certain unrefrigerated low-TSH sera. Measurement of TSH in four human serum pools (TSH < 0.05-0.25 mIU/L) by 16 different methods (each in at least eight UK or US laboratories) showed that some methods could not reliably distinguish subnormal from normal TSH values. Better pool rankings and fewer misclassifications of low-TSH sera as "normal" were seen with use of assays capable of "third-generation" functional sensitivity (0.01-0.02 mIU/L) than with assays with "second-generation" functional sensitivity (0.1-0.2 mIU/L). Because inter- and intramethod differences in functional sensitivity negatively impact the diagnostic accuracy and cost-effectiveness of a TSH-centered thyroid-testing strategy, laboratories should independently establish an assay's functional sensitivity by a clinically relevant protocol. Moreover, manufacturers should assess functional sensitivity more realistically and improve the robustness of assays to ensure that their performance potential is consistently met in clinical practice.

Multiphasic thyrotropin responses to thyroid hormone administration in man

The magnitude and temporal pattern of serum TSH suppression after single or multiple doses of thyroid hormone (T3, T4, or triiodothyroacetic acid) were studied using third and fourth generation TSH assays (sensitivities, 0.01 and 0.001 mU/L, respectively). A constant T3 dose (263 micrograms i.v.) administered at a uniform clock time (1200 h) produced identical serum TSH suppression patterns, (percent of control TSH vs. hours) in euthyroid and hypothyroid subjects. The percent log TSH vs. log time plot revealed three temporally distinct linear suppression phases: phase 1, a rapid TSH suppression, onset 1 h and lasting for 10-20 h; phase 2, slower suppression, onset between 10 and 20 h and lasting for 6-8 weeks; and phase 3, an invariable low TSH level (< 0.01 mU/L) with chronic T3 suppression (100 micrograms four times a day). TSH escaped maximal suppression at a similar serum T3 level in both euthyroid and hypothyroid subjects (2.9 +/- 0.2 vs. 3.5 +/- 0.5 nmol/L, respectively; P > 0.9), despite different basal serum T3 values (2.0 +/- 0.1 vs. 0.6 +/- 0.1 nmol/L, respectively; P < 0.01). Two milligrams of triiodothyroacetic acid or 2 mg T4 given iv at 1200 h produced TSH suppression patterns similar to T3. The phase 1 suppression varied with the clock time of T3 administration, (steeper responses were seen at 2400 vs. 1200 h), whereas phase 2 responses were unaltered. This study shows that thyroid hormone suppression of TSH is a complex, biphasic, nonlinear process, which is reproducible and independent of thyroid status or the thyroid hormone analog used. It is hypothesized that phase 1 reflects inhibition of release of preformed hormone, whereas phase 2 likely reflects inhibition of de novo synthesis and/or thyrotroph storage of TSH. In contrast, phase 3 secretion seems to represent basal constitutive TSH release, which may have relevance to the role of thyroid hormone-suppressive therapy in the treatment of patients with benign or neoplastic thyroid disease.

Identification of a sequence motif upstream of the Drosophila dopa decarboxylase gene that enhances heterologous gene expression

In this paper we have examined the role that element S, a DNA sequence motif found approximately 215 bp upstream of the Dopa decarboxylase (Ddc) gene, might play in regulating Ddc expression. Nearly identical versions of the element are present upstream of four other Drosophila genes. For two of these, the element appears to be an important component of the upstream regulatory region, since mutations in it reduce expression of the downstream gene. Because an element S polymorphism differentiates the Ddc+ allele of an inbred laboratory strain from the Ddc+4 allele present in a strain isolated from the wild, we decided to test the activity of both forms. Oligonucleotides containing Ddc+ or Ddc+4 versions of element S were synthesized and their ability to drive the expression of an heterologous (Adh) reporter gene at the second molt was examined. Transgenic larvae carrying the element S-Adh fusion constructs consistently exhibited Adh levels that were elevated 1.5-fold above those seen in control organisms. We have also determined the effects of element S in white prepupae and once again, ADH expression levels were significantly above controls in both groups of transformants carrying the element S construct. The results point to a functional role for element S. Since reporter gene expression in third instar larvae was restricted to tissues where ADH is normally found, we conclude that element S is not involved in directing the tissue specificity of Ddc expression.(ABSTRACT TRUNCATED AT 250 WORDS)

RNA polymerase II is aberrantly phosphorylated and localized to viral replication compartments following herpes simplex virus infection

During lytic infection, herpes simplex virus subverts the host cell RNA polymerase II transcription machinery to efficiently express its own genome while repressing the expression of most cellular genes. The mechanism by which RNA polymerase II is directed to the viral delayed-early and late genes is still unresolved. We report here that RNA polymerase II is preferentially localized to viral replication compartments early after infection with herpes simplex virus type 1. Concurrent with recruitment of RNA polymerase II into viral compartments is a rapid and aberrant phosphorylation of the large subunit carboxy-terminal domain (CTD). Aberrant phosphorylation of the CTD requires early viral gene expression but is not dependent on viral DNA replication or on the formation of viral replication compartments. Localization of RNA polymerase II and modifications to the CTD may be instrumental in favoring transcription of viral genes and repressing specific transcription of cellular genes.

Chemiluminescent third-generation assay (Amerlite TSH-30) of thyroid-stimulating hormone in serum or plasma assessed

We assessed the laboratory performance and clinical utility of a new commercial third-generation assay of thyroid-stimulating hormone (TSH), Amerlite TSH-30. The interassay CV was 6% at TSH concentrations of approximately 0.08 mIU/L, and the analytical and functional detection limits of the assay were 0.005 and 0.0125 mIU/L, respectively. Although the assay recovered approximately 96% of TSH International Reference Preparation (TSH-IRP) 80/558 added to serum samples, the endogenous TSH concentrations in basal samples were significantly lower than those found by using two other TSH assays; bias data obtained from thyroliberin stimulation tests suggested that the negative bias found with TSH-30 may be due to the heterogeneity of TSH in basal samples. TSH-30 completely discriminated hyperthyroid and hypothyroid patients from euthyroid ambulatory patients but also detected TSH (> 0.0125 mIU/L) in 3 of 46 untreated hyperthyroid patients. Compared with two second-generation assays, TSH-30 better discriminated between patients with subnormal TSH due to hyperthyroidism, thyroxine overreplacement, and nonthyroidal illness but there was still significant overlap between results for these groups.

Chemiluminescent third-generation assay (Amerlite TSH-30) of thyroid-stimulating hormone in serum or plasma assessed

We assessed the laboratory performance and clinical utility of a new commercial third-generation assay of thyroid-stimulating hormone (TSH), Amerlite TSH-30. The interassay CV was 6% at TSH concentrations of approximately 0.08 mIU/L, and the analytical and functional detection limits of the assay were 0.005 and 0.0125 mIU/L, respectively. Although the assay recovered approximately 96% of TSH International Reference Preparation (TSH-IRP) 80/558 added to serum samples, the endogenous TSH concentrations in basal samples were significantly lower than those found by using two other TSH assays; bias data obtained from thyroliberin stimulation tests suggested that the negative bias found with TSH-30 may be due to the heterogeneity of TSH in basal samples. TSH-30 completely discriminated hyperthyroid and hypothyroid patients from euthyroid ambulatory patients but also detected TSH (&gt; 0.0125 mIU/L) in 3 of 46 untreated hyperthyroid patients. Compared with two second-generation assays, TSH-30 better discriminated between patients with subnormal TSH due to hyperthyroidism, thyroxine overreplacement, and nonthyroidal illness but there was still significant overlap between results for these groups.

Thyrotropin (TSH)-releasing hormone stimulation test responses employing third and fourth generation TSH assays

TRH stimulation tests (n = 1109) were performed on 1061 ambulatory and 43 hospitalized patients with varying thyroid status, using a TSH immunochemiluminometric assay with third and fourth generation sensitivity characteristics (functional sensitivity, 0.01 and 0.001 mU/L, respectively). TRH test results were analyzed as both absolute (stimulated minus basal TSH) and fold (stimulated/basal TSH) responses. The absolute TRH response varied 8-fold across the physiological TSH range, whereas the mean fold response remained almost constant (mean +/- SEM, 8.5 +/- 0.2). The fold response became progressively attenuated as basal TSH values declined below physiological levels, becoming essentially absent in clinically thyrotoxic patients with markedly depressed basal serum TSH levels (0.007 +/- 0.002 mU/L). Progressive attenuation also occurred at hypothyroid TSH levels; a markedly impaired fold response (2.5 +/- 0.4) was characteristic of primary hypothyroid patients with basal TSH values greater than 50 mU/L. In untreated central hypothyroid patients with near-normal basal TSH levels, the TRH fold response was impaired (1.7 +/- 0.2), whereas in T4-replaced central hypothyroid patients, fold responses were near normal (5.6 +/- 1.2). Neither nonthyroidal illness, age, or sex appeared to influence the pattern of fold TRH response in the populations evaluated. When using third and fourth generation TSH methodology, the TRH-stimulated TSH fold response is more diagnostically useful than the absolute TRH response. However, if patients have an intact hypothalamic-pituitary axis, there appears to be no diagnostic advantage gained by TRH testing over an accurately measured basal TSH value.

Transcription elongation in the human c-myc gene is governed by overall transcription initiation levels in Xenopus oocytes

Both transcription initiation and transcription elongation contribute to the regulation of steady-state c-myc RNA levels. We have used the Xenopus oocyte transcription assay to study premature transcription termination which occurs in the first exon and intron of the human c-myc gene. Previous studies showed that after injection into Xenopus oocytes transcription from the c-myc P1 promoter resulted in read-through transcripts whereas transcription from the stronger P2 promoter resulted in a combination of prematurely terminated and read-through transcripts. We now demonstrate that this promoter-specific processivity results from the overall amount of RNA polymerase II transcription occurring from either promoter. Parameters that reduce the amount of transcription from P1 or P2, such as decreased concentration of template injected or decreased incubation time, result in a reduction in the ratio of terminated to read-through c-myc transcripts. Conversely, when transcription levels are increased by higher concentrations of injected template, increased incubation time, or coinjection with competing template, the ratio of terminated to read-through transcripts increases. We hypothesize that an RNA polymerase II processivity function is depleted above a threshold level of transcription initiation, resulting in high levels of premature transcription termination. These findings account for the promoter-specific effects on transcription elongation previously seen in this assay system and suggest a mechanism whereby limiting transcription elongation factors may contribute to transcription regulation in other eukaryotic cells.

Rostral cerebellar malformation, (rcm): a new recessive mutation on chromosome 3 of the mouse

A new recessive mutation in the mouse that causes a disorderly arrangement of Purkinje and granule cells in the rostral portion of the cerebellum is described. The mutation, called rostral cerebellar malformation, rcm, has been located on chromosome (Chr) 3 between the alcohol dehydrogenase-3 (Adh-3) complex and varitint waddler-J (VaJ).

Genetic and age related models of neurodegeneration in mice: dystrophic axons

Dystrophic axons (DA) are non-specific lesions that occur in a wide variety of human and animal diseases. In this paper we describe the distribution of these lesions in three newly discovered mouse neurological mutants. The distribution of DA in these mutants is defined by their names, lumbosacral neuroaxonal dystrophy (lnd), located on Chromosome 7, generalized neuroaxonal dystrophy (gnd) and vestibulomotor degeneration (vmd). The last mutant, which has degeneration as well as DA in lateral vestibular nucleus and vestibulo-spinal tracts, dies in the first weeks of life; the first two live for approximately one year. A previously described mutation, dystonia musculorum (dt), was found to produce generalized DA like gnd, but dt/dt mutants die at an early age. DA were also found to occur in the nuclei gracilis and cuneatus, in the area of Clark's column and in lumbo-sacral spinal cord in aging normal mice either fed ad libitum or at a level of 40% dietary restriction. The dietary regimen had little effect on the numbers of DA observed in susceptible areas of the neuroaxis. The mutant models of neuroaxonal dystrophy may prove useful in studies of the pathophysiology of DA in general and of specific inherited diseases of man, such as infantile neuroaxonal dystrophy and Hallervordin-Spatz disease.

Characteristics of 3,5,3'-triiodothyronine sulfate metabolism in euthyroid man

The sulfated conjugate of T3 (T3S) has long been recognized as a normal product of peripheral thyroid hormone metabolism. In order to better understand the role that T3S may play in this process, the metabolic handling of T3S was studied in euthyroid man. After the iv administration of [125I]T3S in man, T3S was found to be rapidly metabolized with estimated mean MCR of 135 +/- 15 liters/day (L/D) after a bolus injection and 127 +/- 8 L/D employing a constant infusion. The primary route of T3S disposal was by deiodination with an efficiency of 92%. The administration of propylthiouracil (PTU, 300 mg every 6 h x 5 days) and iopanoic acid (IA, 500 mg every day x 5 days), both inhibitors of deiodination, decreased clearance compared to control (87 +/- 9 L/D, P less than 0.01 and 46 +/- 10 L/D, P less than 0.002, respectively). A 3-day fast also reduced the clearance of T3S (56 +/- 10 L/D, P less than 0.002). All three maneuvers decreased the total urinary deiodination fraction of tracer T3S (control 91 +/- 2%, PTU 70 +/- 9%, P less than 0.04, IA 26 +/- 3%, P less than 0.0001, and fasting 58 +/- 6%, P less than 0.01). A strong correlation between T3S clearance and deiodination was noted for fasting and IA only (r = 0.78, P less than 0.003). However, no relationship between clearance and deiodination was noted with PTU administration presumably as a result of a compensatory increase in biliary losses of T3S. The urinary thyronine excretion pattern demonstrated the presence of small amounts of labeled T3,3,3'-T2, and 3,3'-T2S with the major metabolite being T3S itself. TSH levels were not influenced by the infusion of stable T3S designed to achieve a serum value greater than 50 ng/dL. No absorption of intact T3S was detected after its oral ingestion. In conclusion, T3S is rapidly cleared from the serum, primarily by deiodination, may undergo nondeiodinative disposal when hepatic deiodination is inhibited by PTU but not with IA or fasting, and has no intrinsic biological activity. Thus, T3S may serve as a metabolite of T3 for its rapid deiodinative disposal. Although the precise role T3S plays in human thyroid hormone metabolism has not been defined, the metabolic characteristics of T3S appear similar to that of an unidentified alternate T4 metabolite formed in low T3 states of fasting and nonthyroidal illness.