The interpretation of the serum protein-bound iodine: A review

Adjustment of the iodine ICRP population pharmacokinetic model for the use in thyroid cancer patients after thyroidectomy

Biokinetic models developed for healthy humans are not appropriate to describe biokinetics in thyroid cancer patients following thyroidectomy. The aim of this study was to adjust the population model for iodine proposed by the International Commission on Radiological Protection (ICRP) for the use in these patients. Rate constants of the ICRP publication 128 model for iodine were adjusted using the population modelling software package Monolix to describe activity retention in whole-body, thyroid, blood and protein-bound iodine observed in 23 patients. The new set of rate constants was compared to the four uptake scenarios proposed in ICRP publication 128. Flow from the inorganic iodide in blood compartment into the first thyroid compartment decreases to 0.15 d^-1compared to a value of 7.27 d^-1for the ICRP publication 128 model with a medium uptake. The transfer from first to second thyroid compartments and the outflow from the second thyroid compartment increases. An increased turnover rate of extrathyroidal organic iodine is observed. The rate constant from inorganic iodide in blood to kidney was also adjusted. Overall a good agreement was found between the adjusted model and the activity retention in thyroid cancer patients. The adjustment of population pharmacokinetic models to describe the biokinetic properties of specific patient populations for therapeutic radiopharmaceuticals is essential to capture the changes in biokinetics. The proposed set of rate constants for the established ICRP publication 128 model can be used to more accurately assess radiation protection requirements for the treatment of thyroid cancer patients using radioiodine.

Utilization Management in a Large Community Hospital

The utilization management of laboratory tests in a large community hospital is similar to academic and smaller community hospitals. There are numerous factors that influence laboratory utilization. Outside influences like hospitals buying physician practices, increasing numbers of hospitalists, and hospital consolidation will influence the number and complexity of the test menu that will need to be monitored for over and/or under utilization in the central laboratory and reference laboratory. CLIA’88 outlines the four test categories including point-of-care testing (waived) and provider-performed microscopy that need laboratory test utilization management. Incremental cost analysis is the most efficient method for evaluating utilization reduction cost savings. Economies of scale define reduced unit cost per test as test volume increases. Outreach programs in large community hospitals provide additional laboratory tests from non-patients in physician offices, nursing homes, and other hospitals. Disruptive innovations are changing the present paradigms in clinical diagnostics, like wearable sensors, MALDI-TOF, multiplex infectious disease panels, cell-free DNA, and others. Obsolete tests need to be universally defined and accepted by manufacturers, physicians, laboratories, and hospitals, to eliminate access to their reagents and testing platforms.

The use of PBPK models to inform human health risk assessment: case study on perchlorate and radioiodide human lifestage models

Physiologically-based pharmacokinetic (PBPK) models are often submitted to or selected by agencies, such as the U.S. Environmental Protection Agency (U.S. EPA) and Agency for Toxic Substances and Disease Registry, for consideration for application in human health risk assessment (HHRA). Recently, U.S. EPA evaluated the human PBPK models for perchlorate and radioiodide for their ability to estimate the relative sensitivity of perchlorate inhibition on thyroidal radioiodide uptake for various population groups and lifestages. The most well-defined mode of action of the environmental contaminant, perchlorate, is competitive inhibition of thyroidal iodide uptake by the sodium-iodide symporter (NIS). In this analysis, a six-step framework for PBPK model evaluation was followed, and with a few modifications, the models were determined to be suitable for use in HHRA to evaluate relative sensitivity among human lifestages. Relative sensitivity to perchlorate was determined by comparing the PBPK model predicted percent inhibition of thyroidal radioactive iodide uptake (RAIU) by perchlorate for different lifestages. A limited sensitivity analysis indicated that model parameters describing urinary excretion of perchlorate and iodide were particularly important in prediction of RAIU inhibition; therefore, a range of biologically plausible values available in the peer-reviewed literature was evaluated. Using the updated PBPK models, the greatest sensitivity to RAIU inhibition was predicted to be the near-term fetus (gestation week 40) compared to the average adult and other lifestages; however, when exposure factors were taken into account, newborns were found to be populations that need further evaluation and consideration in a risk assessment for perchlorate.

Acute hemolysis following iodine tincture ingestion

Iodine tincture poisoning is uncommon regardless of its widespread use as an antiseptic in daily practice. Previously reported effects of iodine-containing antiseptic poisoning included topical irritation, corrosive effects, allergic response, and hepatic or renal injury, which mainly resulted from complications of topical use during surgical procedures. We herein reported an unusual case of severe hemolysis and acute renal failure following intentional ingestion of iodine tincture containing 60 mg/ml iodine and 40 mg/ml potassium iodide in 70% v/v ethanol. The patient completely recovered 8 weeks later after receiving supportive treatment, plasma exchange, and temporary hemodialysis.

Precocious puberty associated with primary hypothyroidism in a mongol girl

A mongol child suffereing from hypothyroidism who presented with precocious puberty is described. A presumptive diagnosis of idiopathic precocious puberty was first made and she was treated initially with medroxyprogesterone acetate, and later, with cyproterone acetate. The diagnosis of primary hypothyroidism was made late because of misleading results of protein bound iodine estimations. Subsequently, thyroid medication resulted in a prompt return to the normal range of the previously elevated levels of plasma gonadotrophins, thyroid stimulating hormone and plasma and urinary oestrogens, but the serum prolactin remained elevated for several months after therapy was begun.

The assay of urinary thyroid hormones for assessing thyroid function

A competitive protein binding assay for thyroxine (T-4) and a radioimmunoassay for tri-iodothyronine (T-3) were applied to determine the urinary concentrations of these hormones. These measurements were shown to offer excellent diagnostic discrimination between euthyroid, hypothyroid, and hyperthyroid subjects. Urinary T-3 and T-4 levels were not affected by changes in the concentration of thyroxine binding globulin (TBG) or by changes in binding capacity; and therefore, remained normal during pregnancy, oestrogen, and phenytoin therapy. There was no significant circadian variation in urine T-3 excretion. Thus T-3 assays of overnight urine samples could be used in conjunction with dynamic test procedures, such as thyrotrophin (TSH) stimulation test, to enable the rapid assessment of the integrity of the hypothalamic-pituitary-thyroid axis.

Iodine contamination in iodometric measurements of thyroid hormones

The incidence of iodine contamination in serum protein-bound iodine requests was assessed by comparison of results with those of a method using anion-exchange columns to improve specificity. The precision, accuracy, and specificity of the column method was found to be adequate, abnormal elution patterns generally warning where results were affected by contamination. The proportion of discrepancies in results and diagnoses between the two tests showed the protein-bound iodine to be unsatisfactory as a sole test of thyroid hormone levels, or in hypothyroidism, even as a screening test.

Iodine contamination of the serum protein-bound iodine: incidence and clinical significance

Iodine contamination as defined by the combination of a raised (PBI-T(4)I) difference and low (131)I neck uptake was found in 38 (17.5%) of 217 euthyroid patients. Of these, 17 had PBI levels of greater than 20 mug/dl but in the remainder levels were clinically feasible. In only 21 was there a history of exposure to iodine. Two of 12 hypothyroid patients had PBI levels well within normal limits. False elevation of the PBI is thus shown to be common. It is neither always obvious nor can it be easily avoided. The PBI is not an acceptable alternative to T(4) estimation by other methods.

The diagnosis of thyrotoxicosis

Thyrotoxicosis is a clinical syndrome due to excessive amounts of thyroid hormone in the circulation and tissues. Graves' disease, goitre and exophthalmos, is the commonest variety, but in some parts of the world thyrotoxicosis supervenes on the background of a long standing nodular goitre. Other varieties such as ectopic TSH syndromes are very rare.

The diagnostic sequence in practice starts with clinical suspicion and a decision can often be made on the symptoms and signs alone. It is, however, always advisable to confirm the presence or absence of thyrotoxicosis. There has been re-orientation in the simple test procedure used in this respect. Measurements such as serum TSH and serum TSH response to TRH and measurements of serum LATS levels are available only in a few centres and are not discussed in detail.

Tests based on the carriage of thyroid hormones in the blood are preferable to in vivo radionuclide studies, particularly when the patient is thought to be euthyroid. We advise a serum PB¹²⁷I and serum total thyroxine estimation in all patients. If the data are abnormal we add a serum T3 resin estimation to check whether the values are due, for example, to iodine contamination or altered binding.

We advise radionuclide studies in all doubtful cases and measurements such as the 4 hr or 24 hr ¹³¹I uptake and the 48 hr serum PB¹³¹I are very helpful. A thyroid uptake suppression test may be required if there is still doubt. In general those patients going for thyroidectomy or ¹³¹I therapy should have a scan performed. With improved technology much safer radionuclides, such as ¹²³I or ^99mTc, may be usable when thyrotoxicosis is suspected in children or during pregnancy.

Thyroxine "addicts"

Four patients are described who were surreptitiously taking thyroxine-containing tablets. In two cases this caused considerable diagnostic problems. The diagnosis should be considered in patients with clinical features of hyperthyroidism (but without goitres or proptosis), who appear psychiatrically abnormal and whose thyroid function tests show conflicting results.

Changes in the normal range of thyroidal radioiodine uptake

Three series of patients shown to be euthyroid but originally referred for thyroid uptake tests in vivo have been compared. In 1958-59, the ;normal' mean thyroid uptake was 23.5% and 38.2% respectively at four and 24 hours. By 1967, the mean uptakes had dropped to 20.4% and 31.6%-a significant change at both times. By 1972 there was, however, no sign of a further reduction of the mean normal values for thyroid uptake. These results are compared with changes observed in other series in the USA and elsewhere.