Extremely low doses of heparin release lipase activity into the plasma and can thereby cause artifactual elevations in the serum-free thyroxine concentration as measured by equilibrium dialysis

Hypothyroidism

Hypothyroidism, the deficiency of thyroid hormone, is a common condition worldwide. It affects almost all body systems and has a wide variety of clinical presentations from being asymptomatic to, in rare cases, life threatening. The classic symptoms of hypothyroidism include fatigue, lethargy, weight gain, and cold intolerance; however, these symptoms are non-specific and the diagnosis is typically made on biochemical grounds through serum thyroid function tests. The most common cause of hypothyroidism is chronic autoimmune thyroiditis (Hashimoto's thyroiditis), although other causes, including drugs (such as amiodarone, lithium, and immune checkpoint inhibitors), radioactive-iodine treatment, and thyroid surgery, are frequent. Historically, severe iodine deficiency was the most common cause. Reference ranges for thyroid function tests are based on fixed percentiles of the population distribution, but there is increasing awareness of the need for more individualised reference intervals based on key factors such as age, sex, and special circumstances such as pregnancy. Levothyroxine monotherapy is the standard treatment for hypothyroidism; it is safe and inexpensive, restores thyroid function tests to within the reference range, and improves symptoms in the majority of patients. However, 10% of patients have persistent symptoms of ill health despite normalisation of thyroid function tests biochemically and a substantial proportion of patients on levothyroxine have thyroid-stimulating hormone concentrations outside the reference range. Ongoing symptoms despite levothyroxine treatment has led to some patients using liothyronine or desiccated thyroid extract. Taken together, these factors have led to intense debate around the treatment thresholds and treatment strategies for hypothyroidism. In this Seminar, we review the epidemiology, genetic determinants, causes, and presentation of hypothyroidism; highlight key considerations and controversies in its diagnosis and management; and provide future directions for research.

Evaluation of non-thyroidal illness syndrome in shock patients admitted to pediatric intensive care unit in a developing country

During critical illness, children my experience various changes in their thyroid hormone levels. Such changes are termed non-thyroidal illness syndrome (NTI). The extent of change correlates with the severity of the illness and its outcomes in critically ill patients. This study aimed to investigate the correlation between the severity of shock and thyroid hormone derangement. This prospective observational study included forty patients aged one month to five years who were admitted to the pediatric intensive care unit (PICU) with shock. Thyroid function tests were conducted on admission, after shock reversal, and five days later. NTI patterns were observed in 70% of patients. The PIM2 score showed a significant negative correlation with T3 (r =  - 0.353, p = 0.026) and FT3 levels on admission (r =  - 0.417, p = 0.007). Furthermore, after shock reversal, the PIM2 score continued to exhibit significant negative correlations with T4 (r =  - 0.444, p = 0.004), T3 (r =  - 0.329, p = 0.038), FT3 (r =  - 0.355, p = 0.025), and FT4 levels (r =  - 0.379, p = 0.016).    Conclusion: This study underscores the high prevalence of NTI in PICU shock patients and suggests monitoring thyroid hormone levels for outcome prediction and treatment guidance. Further research is needed to optimize NTI management in critically ill children. What is Known: • Non-thyroidal illness syndrome (NTIS) is a condition observed in critically ill patients. • There has been limited research on NTI in children, and existing studies have generated conflicting results regarding the relationship between thyroid hormones and clinical outcomes in cases of sepsis and septic shock. What is New: • The study has revealed dynamic changes in free triiodothyronine (FT3) levels during the process of shock reversal and recovery in children who experienced shock. • A significant negative correlation was found between the Pediatric Index of Mortality 2 (PIM2) score and several thyroid hormone levels, including FT3 on admission and T4, FT3, and FT4 on shock reversal.

Analysis of free, unbound thyroid hormones by liquid chromatography-tandem mass spectrometry: A mini-review of the medical rationale and analytical methods

Measurement of hormones is important for the diagnosis and management of endocrine diseases. The thyroid hormones thyroxine (T4) and triiodothyronine (T3) are among the most commonly measured hormones in clinical laboratories, and it is the concentration of free (not bound to proteins) thyroid hormones that is clinically most relevant. Free thyroid hormones are commonly measured using automated immunoassays, however, these are known to produce erroneous results due to interferences for some patients. Measurement of free thyroid hormones using equilibrium dialysis or ultrafiltration combined with liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) is considered a more accurate and robust method for free thyroid hormone analysis and overcomes many of the limitations of immunoassays. However, LC-MS/MS-based methods are often considered too technically difficult and not amendable to high throughput by clinical chemists and are not offered by many clinical laboratories. This mini-review aims to make it easier for clinical laboratories to implement LC-MS/MS-based measurement of free thyroid hormones. It describes the medical rationale for measuring free thyroid hormones, the benefits of LC-MS/MS-based methods with respect to interferences affecting immunoassay-based methods and physical separation methods. This mini-review highlights important parameters for ultrafiltration and equilibrium dialysis to obtain physiologically relevant free thyroid hormone concentrations and focuses on methods and devices used in clinical chemistry.

Free thyroxine measurement in clinical practice: how to optimize indications, analytical procedures, and interpretation criteria while waiting for global standardization

Thyroid dysfunctions are among the most common endocrine disorders and accurate biochemical testing is needed to confirm or rule out a diagnosis. Notably, true hyperthyroidism and hypothyroidism in the setting of a normal thyroid-stimulating hormone level are highly unlikely, making the assessment of free thyroxine (FT4) inappropriate in most new cases. However, FT4 measurement is integral in both the diagnosis and management of relevant central dysfunctions (central hypothyroidism and central hyperthyroidism) as well as for monitoring therapy in hyperthyroid patients treated with anti-thyroid drugs or radioiodine. In such settings, accurate FT4 quantification is required. Global standardization will improve the comparability of the results across laboratories and allow the development of common clinical decision limits in evidence-based guidelines. The International Federation of Clinical Chemistry and Laboratory Medicine Committee for Standardization of Thyroid Function Tests has undertaken FT4 immunoassay method comparison and recalibration studies and developed a reference measurement procedure that is currently being validated. However, technical and implementation challenges, including the establishment of different clinical decision limits for distinct patient groups, still remain. Accordingly, different assays and reference values cannot be interchanged. Two-way communication between the laboratory and clinical specialists is pivotal to properly select a reliable FT4 assay, establish reference intervals, investigate discordant results, and monitor the analytical and clinical performance of the method over time.

Relationship of Preoperative Thyroid Dysfunction to Clinical Outcomes in Pediatric Cardiac Surgery

CONTEXT

Thyroid function may be assessed in children before cardiac surgery because of concerns that hypothyroidism or thyrotoxicosis might adversely affect cardiac function perioperatively. However, the relationship between preoperative thyroid dysfunction and surgical outcomes is unknown.

OBJECTIVE

Determine the relationship between preoperative thyroid dysfunction and outcomes of pediatric cardiac surgery.

METHODS

Retrospective cohort study (January 2005 to July 2019).

SETTING

Academic pediatric hospital.

PATIENTS

All patients <19 years old who underwent cardiac surgery with cardiopulmonary bypass and had thyrotropin (TSH) measured within 14 days preoperatively. Exclusion criteria included neonates (≤30 days), preoperative extracorporeal life support, salvage operations, or transplantation procedures.

MAIN OUTCOME MEASURES

Subjects were stratified by preoperative TSH concentration (mIU/L): low (<0.5), normal (0.5-5), mildly high (5.01-10), or moderately high (>10). Outcomes were compared among subjects with normal TSH (control) and each group with abnormal TSH concentrations. The primary outcome was 30-day mortality. Secondary outcomes included time to extubation, intensive care unit and hospital length of stay, and operative complications.

RESULTS

Among 592 patients analyzed, preoperative TSH was low in 15 (2.5%), normal in 347 (58.6%), mildly high in 177 (29.9%), and moderately high in 53 (9.0%). Free thyroxine was measured in 77.4% of patients and was low in 0 to 4.4% of subjects, with no differences among TSH groups. Thirty-day mortality was similar among TSH groups. There were no differences in any secondary outcome between patients with abnormal TSH and patients with normal TSH.

CONCLUSION

Preoperative mild to moderate subclinical hypothyroidism was not associated with adverse postoperative outcomes in children undergoing cardiopulmonary bypass procedures.

Administration of low and high doses of heparin causes changes in plasma non-esterified fatty acid concentration in merino and terminal sired lambs

Context The anticoagulant properties of heparin have led to the routine use of heparinised saline flushes to prevent thrombus formation and to prolong the patency of indwelling cannulas. However, limited work exists on very low-dose heparin used to retain cannula patency for the purpose of repeated blood sampling for metabolic studies. Of particular interest is whether low-dose heparin will cause increases in plasma non-esterified fatty acid (NEFA) concentration. This is most relevant in metabolic studies involving repeated sampling, as this may erroneously elevate apparent plasma NEFA concentrations. Aims The objective of the present study was to evaluate the impacts of low- and high-dose heparin administration on plasma NEFA response in lambs. Methods In total, 14 merino (3 female, 4 wether) and terminal (4 female, 3 wether) sired lambs were selected from the Katanning, Western Australia, site of the Meat and Livestock Australia genetic resource flock All lambs were subjected to the following three treatments: low heparin (0.25 mL, 250 IU), high heparin (1 mL, 1000 IU) or control (1 mL of 0.9% NaCl saline), with each challenge being randomly allocated over 1.5 days. Blood samples were collected at the following time points: –30, –15, –10, –5, 0, 2.5, 5, 10, 15, 20, 30, 45, 60, 90, 120, 125 and 130 min relative to the administration of the challenge (Time 0) and tested for NEFA concentration. A derived exponential function was fitted to the raw data, enabling the plasma NEFA concentration response curve to be modelled at different time pointspre- and post-challenge, using the area under curve (AUC), maximum concentration and return to basal concentration, to quantify the NEFA response. Results Heparin-challenge dose had a significant (P &lt; 0.01) impact on peak NEFA response at 10 min following challenge administration (NEFA AUC10), with the values after high-heparin challenge (1.03 ± 0.086 mmol/L per 10 min) being ~25% higher (P &lt; 0.05) than those after the low-heparin challenge (0.78 ± 0.086 mmol/L per 10 min). The NEFA AUC10 values with low-dose heparin and high-dose heparin were 0.76 units and 1.02 units higher than those with the saline treatment (0.02 ± 0.086 mmol/L per 10 min; P &lt; 0.01). Heparin-challenge dose also had a significant impact on the maximum NEFA concentration (P &lt; 0.05). The high-heparin challenge (0.32 ± 0.057 mmol/L) had 20% higher maximum NEFA concentrations than the low-heparin challenge (0.26 ± 0.057 mmol/L). Both high and low heparin-challenge groups had maximum NEFA concentrations that were 72% and 36% higher respectively, than for the saline-challenge (0.19 ± 0.057 mmol/L) group. NEFA returned to basal concentrations by 60 min for both challenges, although the high heparin-challenge group demonstrated a slower rate of return (P &lt; 0.05). Conclusions High and low doses of heparin caused an increase in plasma NEFA response as measured by AUC10 and maximum NEFA concentration, but returned to basal concentrations within 1 h. Implications Results indicated that heparin as an anticoagulant should be avoided where frequent blood samples are required within intervals of less than 1 h. However, for repeated sampling at intervals greater than 1 h, judicious flushing with heparinised saline is unlikely to have an impact on plasma NEFA concentrations.

Evolution of circulating thyroid hormone levels in preterm infants during the first week of life: perinatal influences and impact on neurodevelopment

Background For several decades, transient hypothyroxinemia of prematurity (THOP) has been a topic of debate. The pathophysiology is incompletely understood and consensus on the therapeutic approach is lacking. This study aimed at gaining a better insight into the pathogenesis by studying the trends in thyroid hormone (TH) levels during the first week of life. Methods This single-center prospective observational study analyzed the plasma levels of total thyroxine (T4) and free thyroxine (fT4), total triiodothyronine (T3), thyroid-stimulating hormone (TSH) and T4-binding globulin (TBG) in cord blood and at the end of the first week of life in 120 preterm infants (gestational age [GA] <37 weeks). The change over time was calculated (delta, ∆). The impact of perinatal and subsequently postnatal variables on ∆ was studied by hierarchical multiple regression. The impact of ∆ on the neurodevelopmental outcome at the corrected ages of 9 and 24 months, measured by the Bayley Scales of Infant Development (BSID)-II, was assessed by logistic regression. Results ∆fT4 levels were negatively affected by GA and use of dopamine, whereas only GA was associated with low ∆T3 levels. Negative ∆fT4 levels were present in 75% of the extremely low-for-gestational-age infants, whereas 23.5% had a negative ∆T3 level. There was an increased risk for an abnormal mental developmental score (<85) with decreasing ∆T3 at 9 months, corrected age, but not at 24 months. Conclusions A negative evolution in circulating TH levels is principally an immaturity phenomenon, whereas dopamine can further suppress the hypothalamic-pituitary-thyroid axis. There is at least a temporary negative effect of this evolution on the infants' neurodevelopment.

Interferences With Thyroid Function Immunoassays: Clinical Implications and Detection Algorithm

Automated immunoassays used to evaluate thyroid function are vulnerable to different types of interference that can affect clinical decisions. This review provides a detailed overview of the six main types of interference known to affect measurements of thyroid stimulating hormone (TSH), free thyroxine (T4) and free triiodothyronine (T3): macro-TSH, biotin, antistreptavidin antibodies, anti-ruthenium antibodies, thyroid hormone autoantibodies, and heterophilic antibodies. Because the prevalence of some of these conditions has been reported to approach 1% and the frequency of testing for thyroid dysfunction is important, the scale of the problem might be tremendous. Potential interferences in thyroid function testing should always be suspected whenever clinical or biochemical discrepancies arise. Their identification usually relies on additional laboratory tests, including assay method comparison, dilution procedures, blocking reagents studies, and polyethylene glycol precipitation. Based on the pattern of thyroid function test alterations, to screen for the six aforementioned types of interference, we propose a detection algorithm, which should facilitate their identification in clinical practice. The review also evaluates the clinical impact of thyroid interference on immunoassays. On review of reported data from more than 150 patients, we found that ≥50% of documented thyroid interferences led to misdiagnosis and/or inappropriate management, including prescription of an unnecessary treatment (with adverse effects in some situations), inappropriate suppression or modification of an ongoing treatment, or use of unnecessary complementary tests such as an I123 thyroid scan. Strong interaction between the clinician and the laboratory is necessary to avoid such pitfalls.

Hypothyroidism

Hypothyroidism is a common condition of thyroid hormone deficiency, which is readily diagnosed and managed but potentially fatal in severe cases if untreated. The definition of hypothyroidism is based on statistical reference ranges of the relevant biochemical parameters and is increasingly a matter of debate. Clinical manifestations of hypothyroidism range from life threatening to no signs or symptoms. The most common symptoms in adults are fatigue, lethargy, cold intolerance, weight gain, constipation, change in voice, and dry skin, but clinical presentation can differ with age and sex, among other factors. The standard treatment is thyroid hormone replacement therapy with levothyroxine. However, a substantial proportion of patients who reach biochemical treatment targets have persistent complaints. In this Seminar, we discuss the epidemiology, causes, and symptoms of hypothyroidism; summarise evidence on diagnosis, long-term risk, treatment, and management; and highlight future directions for research.

Low T3 syndrome and long-term mortality in chronic hemodialysis patients

AIM: To investigate the predictive value of low freeT3 for long-term mortality in chronic hemodialysis (HD) patients and explore a possible causative role of chronic inflammation.

METHODS: One hundred fourteen HD patients (84 males) consecutively entered the study and were assessed for thyroid function and two established markers of inflammation, high sensitivity C-reactive protein (hsCRP) and interleukin-6 (IL-6). Monthly blood samples were obtained from all patients for three consecutive months during the observation period for evaluation of thyroid function and measurement of inflammatory markers. The patients were then divided in two groups based on the cut-off value of 1.8 pg/mL for mean plasma freeT3, and were prospectively studied for a mean of 50.3 ± 30.8 mo regarding cumulative survival. The prognostic power of low serum fT3 levels for mortality was assessed using the Kaplan-Meier method and univariate and multivariate regression analysis.

RESULTS: Kaplan-Meier survival curve showed a negative predictive power for low freeT3. In Cox regression analysis low freeT3 remained a significant predictor of mortality after adjustment for age, diabetes mellitus, hypertension, hsCRP, serum creatinine and albumin. Regarding the possible association with inflammation, freeT3 was correlated with hsCRP, but not IL-6, and only at the first month of the study.

CONCLUSION: In chronic hemodialysis patients, low plasma freeT3 is a significant predictor of all-cause mortality. Further studies are required to identify the underlying mechanisms of this association.

Treatment with thyroid hormone

Thyroid hormone deficiency can have important repercussions. Treatment with thyroid hormone in replacement doses is essential in patients with hypothyroidism. In this review, we critically discuss the thyroid hormone formulations that are available and approaches to correct replacement therapy with thyroid hormone in primary and central hypothyroidism in different periods of life such as pregnancy, birth, infancy, childhood, and adolescence as well as in adult patients, the elderly, and in patients with comorbidities. Despite the frequent and long term use of l-T4, several studies have documented frequent under- and overtreatment during replacement therapy in hypothyroid patients. We assess the factors determining l-T4 requirements (sex, age, gender, menstrual status, body weight, and lean body mass), the major causes of failure to achieve optimal serum TSH levels in undertreated patients (poor patient compliance, timing of l-T4 administration, interferences with absorption, gastrointestinal diseases, and drugs), and the adverse consequences of unintentional TSH suppression in overtreated patients. Opinions differ regarding the treatment of mild thyroid hormone deficiency, and we examine the recent evidence favoring treatment of this condition. New data suggesting that combined therapy with T3 and T4 could be indicated in some patients with hypothyroidism are assessed, and the indications for TSH suppression with l-T4 in patients with euthyroid multinodular goiter and in those with differentiated thyroid cancer are reviewed. Lastly, we address the potential use of thyroid hormones or their analogs in obese patients and in severe cardiac diseases, dyslipidemia, and nonthyroidal illnesses.

Pitfalls in the measurement and interpretation of thyroid function tests

Thyroid function tests (TFTs) are amongst the most commonly requested laboratory investigations in both primary and secondary care. Fortunately, most TFTs are straightforward to interpret and confirm the clinical impression of euthyroidism, hypothyroidism or hyperthyroidism. However, in an important subgroup of patients the results of TFTs can seem confusing, either by virtue of being discordant with the clinical picture or because they appear incongruent with each other [e.g. raised thyroid hormones (TH), but with non-suppressed thyrotropin (TSH); raised TSH, but with normal TH]. In such cases, it is important first to revisit the clinical context, and to consider potential confounding factors, including alterations in normal physiology (e.g. pregnancy), intercurrent (non-thyroidal) illness, and medication usage (e.g. thyroxine, amiodarone, heparin). Once these have been excluded, laboratory artefacts in commonly used TSH or TH immunoassays should be screened for, thus avoiding unnecessary further investigation and/or treatment in cases where there is assay interference. In the remainder, consideration should be given to screening for rare genetic and acquired disorders of the hypothalamic-pituitary-thyroid (HPT) axis [e.g. resistance to thyroid hormone (RTH), thyrotropinoma (TSHoma)]. Here, we discuss the main pitfalls in the measurement and interpretation of TFTs, and propose a structured algorithm for the investigation and management of patients with anomalous/discordant TFTs.

The impact of low triiodothyronine levels on mortality is mediated by malnutrition and cardiac dysfunction in incident hemodialysis patients

OBJECTIVE

Little is known about the impact of low triiodothyronine (T3) levels on mortality in end-stage renal disease (ESRD) patients starting hemodialysis (HD) and whether this impact is mediated by malnutrition, inflammation, or cardiac dysfunction.

DESIGN AND METHODS

A prospective cohort of 471 incident HD patients from 36 dialysis centers within the Clinical Research Center for ESRD in Korea was selected for this study. Based on the median value of T3, patients were divided into 'higher' and 'lower' groups, and all-cause and cardiovascular (CV) mortality rates were compared. In addition, associations between T3 levels and various nutritional, inflammatory, and echocardiographic parameters were determined.

RESULTS

Compared with those in the 'higher' T3 group, albumin, cholesterol, and triglyceride levels, lean body mass estimated by creatinine kinetics (LBM-Cr), and normalized protein catabolic rate (nPCR) were significantly lower in patients with 'lower' T3 levels. The 'lower' T3 group also had a higher left ventricular mass index (LVMI) and a lower ejection fraction (EF). Furthermore, correlation analysis revealed significant associations between T3 levels and nutritional and echocardiographic parameters. All-cause and CV mortality rates were significantly higher in patients with 'lower' T3 levels than in the 'higher' T3 group (113.4 vs 18.2 events per 1000 patient-years, P<0.001, and 49.8 vs 9.1 events per 1000 patient-years, P=0.001, respectively). The Kaplan-Meier analysis also showed significantly worse cumulative survival rates in the 'lower' T3 group (P<0.001). In the Cox regression analysis, low T3 was an independent predictor of all-cause mortality even after adjusting for traditional risk factors (hazard ratio=3.76, P=0.021). However, the significant impact of low T3 on all-cause mortality disappeared when LBM-Cr, nPCR, LVMI, or EF were incorporated into the models.

CONCLUSION

Low T3 has an impact on all-cause mortality in incident HD patients, partly via malnutrition and cardiac dysfunction.

The effect of medications on thyroid function tests

Drug-induced thyroid disorders are common in clinical practice. It is important to recognize the various drugs contributing to thyroid dysfunction for a timely intervention to help achieve a euthyroid state. The pathways of thyroid hormone synthesis, secretion, transport, metabolism, and absorption offer numerous targets for medication interactions. This article discusses some of the medications that may influence thyroid function tests.

Lipids in critical care medicine

While enteral nutrition is the basis for the critically ill, parenteral nutrition is often used when a sufficient enteral nutrition is not or not fully achievable. Lipids are a mainstay of caloric supply in both cases as they combine the provision of building blocks for the membranes and are precursors for function molecules including lipid mediators bearing the ability to influence immunity. Pro-inflammatory lipid mediators as prostaglandins and leukotrienes are generated from arachidonic acid (AA), a key member of the n-6 polyunsaturated fatty acids (PUFA). In contrast, lipid mediators derived from the n-3 fatty acids eicosapentaenoic acid (EPA) or docosahexaenoic acid (DHA) may exhibit less inflammatory properties compared to their AA-derived counterparts. Furthermore, intercellular mediators as resolvins and protectins are generated from n-3 fatty acids. They induce the resolution of inflammation, hence the name resolution phase interaction product-resolvin. Modulating the amount of PUFA and the n-6/n-3 ratio were investigated as means to change the inflammatory response and improve the outcome of patients. Experimental data showed that n-3 fatty acids may improve acute lung injury and sepsis in animal models. Studies in patients undergoing major surgery with application of n-3 fatty acids demonstrated beneficial effects in terms of reduction of length of stay and infectious complications. Clinical data hints that this concept may also improve outcome in critically ill patients. Additionally, experimental and clinical data suggest that a reduction in n-6 PUFA may change the immune response. In conclusion, modulating the amount of PUFA, the n-6/n-3 ratio and the composition of lipid emulsions may prove to be a useful means to improve the outcome of critically ill patients.

The measurement, definition, aetiology and clinical consequences of neonatal transient hypothyroxinaemia

This review focuses on neonatal transient hypothyroxinaemia, a condition characterized by temporary postnatal reductions in concentrations of Total T4 or Free T4, with normal or low concentrations of thyroid stimulating hormone (TSH). There is neither an agreed quantitative definition, nor an agreed mode of measurement for the condition. Transient hypothyroxinaemia is not routinely monitored yet it is thought to affect about 50% of preterm infants; it was thought to be without long-term sequelae but observational studies indicate that neurodevelopment may be compromised. The aetiology of transient hypothyroxinaemia is complex. There are significant contributions from the withdrawal of maternal-placental thyroxine transfer, hypothalamic-pituitary-thyroid immaturity, developmental constraints on the synthesis and peripheral metabolism of iodothyronines and iodine deficiency. It is not possible to distinguish clinically, or from laboratory measurements, whether transient hypothyroxinaemia is an independent condition or simply a consequence of non-thyroidal illness and/or drug usage. An answer to this question is important because studies of thyroid hormone replacement have been instigated, with mixed results. Until the aetiology of transient hypothyroxinaemia is better understood it would seem prudent not to routinely supplement preterm infants with thyroid hormones. Iodine deficiency, non-thyroidal illness and drug usage are the most modifiable risk factors for transient hypothyroxinaemia and are the clear choices for attempts at reducing its incidence. We suggest that transient hypothyroxinaemia in preterm infants is defined as a normal or low TSH concentration in conjunction with a concentration of Total T4, that is ≤10th percentile of cord Total T4 of the equivalent gestational age had the infant remained in utero.

Drug-induced endocrine disorders in the intensive care unit

The neuroendocrine response to critical illness is key to the maintenance of homeostasis. Many of the drugs administered routinely in the intensive care unit significantly impact the neuroendocrine system. These agents can disrupt the hypothalamic-pituitary-adrenal axis, cause thyroid abnormalities, and result in dysglycemia. Herein, we review major drug-induced endocrine disorders and highlight some of the controversies that remain in this area. We also discuss some of the more rare drug-induced syndromes that have been described in the intensive care unit. Drugs that may result in an intensive care unit admission secondary to an endocrine-related adverse event are also included. Unfortunately, very few studies have systematically addressed drug-induced endocrine disorders in the critically ill. Timely identification and appropriate management of drug-induced endocrine adverse events may potentially improve outcomes in the critically ill. However, more research is needed to fully understand the impact of medications on endocrine function in the intensive care unit.

Medications that distort in vitro tests of thyroid function, with particular reference to estimates of serum free thyroxine

The combination of serum thyroid-stimulating hormone (TSH) with measurement of circulating thyroid hormones greatly improves sensitivity and specificity of thyroid diagnosis, but these assays are not impeccable. Estimation of serum free T4 conveniently accommodates variations in the concentration of thyroxine-binding globulin (TBG), but no current technique reliably reflects the in vivo free T4 concentration in numerous other situations. The effect of circulating competitors that increase T4 and T3 in vivo, in particular, many medications, is under-estimated by current free hormone estimates that involve sample dilution. Non-esterified fatty acids generated during sample storage and incubation can spuriously increase the measured free T4 estimate, especially after in vivo treatment with heparin. These artefacts are unlikely to be overcome by current assay strategies. Total serum T4, corrected for alterations in TBG concentration, gives a more robust estimate of thyroxine concentration than current methods of free hormone estimation and should now be reintroduced as the 'gold standard'.

Fish oil in critical illness

PURPOSE OF REVIEW

The aim of this review is to discuss recent advances in the role of n-3 lipids derived from fish oil in clinical nutrition in an intensive care setting.

RECENT FINDINGS

Fish oil supplies n-3 fatty acids which compete with arachidonic acid (n-6) for the conversion to lipid mediators, influence lipid-bound second messenger generation and dependent cellular functions, and are a source for resolvins necessary for the resolution of inflammation. Enteral nutrition with n-3 fatty acids improved ventilation time in patients with acute lung injury and in one study reduced mortality in septic patients. Using a high-dose short-term infusion of fish oil-based lipid emulsion, rapid immunologic changes and effects on the endotoxin-induced stress response may be achieved. Inclusion of n-3 fatty acids in parenteral nutrition improved immunologic parameters and length of stay in surgical patients.

SUMMARY

Inclusion of fish oil in nutrition may influence the immune response and clinical outcomes by balancing the negative effects of n-6 fatty acids. Application as a part of enteral immunonutrition in surgical or acute respiratory distress syndrome patients and in lipid emulsions in surgical patients has beneficial effects. In septic patients, data on enteral use are highly controversial. Prospective data from randomized trials, however, are lacking.

Endocrine assessments during critical illness

The evaluation of hormonal status in critically ill patients is challenging and has many pitfalls. This article reviews proper assessment of glycemic status AND adrenal and thyroid function during critical care.

Non-thyroidal illness syndrome is a manifestation of hypothalamic-pituitary dysfunction, and in view of current evidence, should be treated with appropriate replacement therapies

This article documents the role of hypothalamic hypothyroidism and decreased T4-->T3 conversion as the cause of low T4 and T3 in non-thyroidal illness syndrome (NTIS). This article also presents the arguments for administration of replacement triiodothyronine (T3) and thyroxine (T4) hormone in patients who have NTIS. It is impossible to be certain at this time that it is beneficial to replace hormone, or whether this could be harmful. Only a prospective study will be adequate to prove this point, and probably this would need to involve hundreds of patients. If effective, thyroid hormone replacement will be one of many beneficial treatments given the patient, rather than a single magic bullet, which would reverse all the metabolic changes going wrong in these severely ill patients.

Incidence of low free T4 values in premature infants as determined by direct equilibrium dialysis

BACKGROUND

The incidence of transient reductions in serum free T(4) (FT(4)) in premature infants may be overestimated because certain FT(4) analytical methods underestimate FT(4) concentrations. Transient reductions of FT(4) measurements have been reported in the majority of premature newborn infants. Direct equilibrium dialysis (DED) does not underestimate FT(4) concentrations and is the best available technique to measure serum FT(4) in the premature infant.

OBJECTIVE

To evaluate the incidence of low FT(4) concentrations in premature infants using DED to measure FT(4).

DESIGN/METHOD

We measured FT(4) by DED in infants with birth weight <1500 g. Infants were excluded if the following conditions were present: congenital anomalies or maternal thyroid disorders. Free T(4) was measured at 14 days of life. Low FT(4) was defined using a statistical definition of FT(4) measurements <10.3 pmol/l (0.8 ng/dl).

RESULTS

Free T(4) was measured by DED in 114 infants. Low FT(4) levels were seen in nine infants (7.9%).

CONCLUSION

The incidence of low FT(4) was much lower than previously reported when FT(4) was measured using DED indicating that methodological issues are involved in the variability among estimates of the frequency of transient reduction in FT(4).

Reference methods for the measurement of free thyroid hormones in blood

In this paper, a review of the literature on the methods for the detection of FT(4) is provided. Furthermore, an overview of the most important uncertainties and interferences of the potential reference methods for determination of free thyroxine (free triiodothyronine) are also presented. Especially, the separation step-dialysis, or ultrafiltration-implies important technical and theoretical uncertainties and interferences as to the methods.Furthermore, a short review of methods based on isotope dilution/mass spectrometry (ID/MS) to quantify thyroxine is provided. There has so far been no attempt to quantify the free fraction of thyroxine by ID/MS, probably due to lack of sensitivity, but if quantification of the free fraction of thyroxine can be done with ID/MS, then this step seems the least compromised step only including minor uncertainties in comparison to the separation step.

Omega-3 vs. omega-6 lipid emulsions exert differential influence on neutrophils in septic shock patients: impact on plasma fatty acids and lipid mediator generation

OBJECTIVE

To compare the effects of a conventional omega-6 lipid infusion and a fish oil based (omega-3) lipid infusion for parenteral nutrition on neutrophil function, lipid mediators, and plasma free fatty acids.

DESIGN AND SETTING

Open-label, randomized, pilot study in a university hospital medical intensive care unit and experimental laboratory.

PATIENTS AND PARTICIPANTS

Ten patients with septic shock and eight healthy controls.

INTERVENTIONS

Patients (five per group) requiring parenteral nutrition received intravenously either a omega-3 or a omega-6 lipid emulsion for a 10-day period.

MEASUREMENTS AND RESULTS

At baseline levels of plasma free fatty acids were elevated several-fold, including high concentrations of the omega-6 lipid precursor arachidonic acid (AA). Neutrophils isolated from septic patients displayed markedly reduced responsiveness to ex vivo stimulation, including lipid mediator generation [leukotrienes (LT), PAF], respiratory burst, and phosphoinositide hydrolysis signaling. Under the omega-6 lipid infusion regimen abnormalities in plasma free fatty acids and impairment of neutrophil functions persisted or worsened. In contrast, a rapid switch in the plasma free fatty acid fraction to predominance of the omega-3 acids eicosapentaenoic acid and docosahexaenoic acid over AA occurred in response to omega-3 lipid infusion. LTB(5), in addition to LTB(4), appeared upon neutrophil stimulation originating from these patients, and neutrophil function was significantly improved in the omega-3 lipid group.

CONCLUSIONS

omega-3 vs. omega-6 lipid emulsions differentially influence the plasma free fatty acid profile with impact on neutrophil functions. Lipid-based parenteral nutrition in septic patients may thus exert profound influence on sequelae and status of immunocompetence and inflammation.

Parenteral nutrition with fish oil modulates cytokine response in patients with sepsis

Infusion of fish oil-based (n-3) lipids may influence leukocyte function and plasma lipids in critical care patients. Twenty-one patients with sepsis requiring parenteral nutrition were randomized to receive an n-3 lipid emulsion rich in eicosapentaenoic acid and docosahexaenoic acid or a conventional (n-6) lipid emulsion (index fatty acid: arachidonic acid) for 5 days. The impact on plasma-free fatty acids, mononuclear leukocyte cytokine generation, and membrane fatty acid composition was examined. Cytokine synthesis by isolated mononuclear leukocyte was elicited by endotoxin. Before the onset of lipid infusion therapy, plasma-free fatty acid concentrations were greatly increased in septic patients, with arachidonic acid by far surpassing eicosapentaenoic acid and docosahexaenoic acid, a feature maintained during conventional lipid infusion. Within 2 days of fish oil infusion, free n-3 fatty acids increased, and the n-3/n-6 ratio was reversed, with rapid incorporation of n-3 fatty acids into mononuclear leukocyte membranes. Generation of proinflammatory cytokines by mononuclear leukocytes was markedly amplified during n-6 and was suppressed during n-3 lipid application. After termination of lipid administration, free n-3 fatty acid concentrations and mononuclear leukocyte cytokine synthesis returned to preinfusion values. Use of lipid infusions might allow us to combine intravenous alimentation with differential impact on inflammatory events and immunologic functions in patients with sepsis.

Euthyroid sick syndrome in acute ischemic syndromes

The purposes of this study were to assess the occurrence of euthyroid sick syndrome in patients with acute myocardial infarction (AMI) or unstable angina (UA), and the relationship with beta-blocker or thrombolytic therapy. Plasma triiodothyronine (T3), reverse T3 (rT3), free T3 (FT3), thyroxine (T4), free T4 (FT4), thyroid-stimulating hormone (TSH), thyroxine-binding globulin (TBG), and albumin (ALB) levels were determined in 95 patients (59 males, 36 females, aged 58.4+/-9) with AMI and 19 patients (13 males, 6 females aged 54.7+/-12.3) with UA for 5 consecutive days from the onset of the acute syndrome and 1 month later. Patients were divided according to beta-blocker therapy and thrombolytic therapy. There was a significant T3 decrease and rT3 increase in all patients during the first 5 days following admission (p < 0.05). FT3 and FT4 remained unchanged during the study. In patients with complicated infarctions, the rT3 increase and the T3 decrease were significantly greater compared to those with uncomplicated infarctions (p<0.03). TSH, T4, TBG, and ALB were significantly (p<0.05) decreased only in complicated infarctions. No differences were observed between patients with or without thrombolysis or patients with or without beta-blocker treatment. The apparent decrease in T3, the increase in rT3 levels and the decreased TSH and T4 levels, show clearly that the euthyroid sick syndrome (low T3) occurs not only in AMI but also in UA. In addition, these hormonal changes are not affected by beta-blocker therapy and thrombolysis does not influence the occurrence of the syndrome. The degree of T3 decrease is proportional to the severity of cardiac damage and may have a possible prognostic value.

Changes in thyroxine requirements in patients with hypothyroidism undergoing renal transplantation

Hypothyroidism is common in the renal failure population and is both influenced by the onset of renal failure and its correction with renal transplantation. We report a series of 20 consecutive patients on oral thyroxine, in which restoration of renal function following transplantation resulted in reduced thyroxine requirements. We speculate that iodide excess, reduced bioavailability, and drug interactions may have contributed both to their hypothyroidism and the increased requirements for thyroxine in these patients while on dialysis. Failure to recognize the changes following renal transplantation may result in significant morbidity.

Parenteral nutrition with n-3 lipids in sepsis

Dietary supplements of n-3 fatty acids have long been used to influence chronic inflammatory disorders. Recent studies with an immune-enhancing diet partly based on n-3 fatty acids report beneficial effects in patients with acute hyper-inflammatory diseases, such as the sepsis syndrome or adult respiratory distress syndrome (ARDS). The possible suppression of exaggerated leucocyte activity, the improvement of microcirculatory events, as well as the opportunity to administer intravenous lipids enriched in n-3 fatty acids signal the possibility of a combination of parenteral caloric support and pharmacological intervention. Using parenteral administration of fish oil-based lipids, a new rapid and highly effective anti-inflammatory agent may allow the option to alter the immune status in hyper-inflammatory diseases such as sepsis and ARDS.

Direct and Indirect Free Thyroxine Assay Methods: Theory and Practice

Background: For the diagnosis of thyroid disease, measurement of “free hormone” is generally accepted as an appropriate measure. However, valid assays measuring the free fraction of thyroxine (FT4) ideally must perform without bias, despite large variations in the concentrations and affinities of serum T4-binding proteins in the population. Several approaches have been taken to overcome such bias, and these have created considerable controversy in the field over the past decade.

Approach: This review, from both a historical and an analytical standpoint, charts the progress made over more than 30 years in improvements to the performance of assays in common use for the measurement of FT4 in serum or plasma. It reexamines the theory behind early approaches to such assays [for example, the free thyroxine index (FTI) method], that preceded more accurate, two-step immunoassays or one-step analog techniques. It evaluates the continuous refinements to the latter assays that by now have largely supplanted the FTI approach and where the deficiencies that so exercised clinical chemists in the past have been virtually eliminated in the leading assays.

Content: The basic Mass Action theory underpinning all such methods is discussed by assessing how far each particular approach obeys the criteria the theory imposes. In this, it is not the intention of the review to dissect individual commercial or academic assays, but rather to give guidance where appropriate as to how any assay said to measure FT4 can be conveniently evaluated by those intending to use it. Examples are given where inappropriate tests may wrongly imply assay invalidity by misinterpreting how FT4 assays work.

Summary: Detailed knowledge of the underlying theory is essential when devising tests for direct FT4 assays, to ensure that such tests do not overstep the practical limits of assay validity.

Free thyroid hormone measurement. A critical appraisal

The main purpose of free T4 and free T3 assays is to distinguish reliably between thyrotoxicosis, hypothyroidism, and the euthyroid state, an objective that cannot be attained with assays of total T4 and T3 because of hereditary and acquired variations in the concentrations of binding proteins. Effective correction for changes in the serum concentration of TBG can be achieved with numerous types of free hormone estimate, but other changes in binding are not well accommodated. Despite remarkable methodologic ingenuity, no current method reflects the free T4 concentration in undiluted serum under in vivo conditions. Equilibrium dialysis, widely considered the reference method for free T4 measurement, is also subject to error, either preanalytic, owing to generation of NEFA in the sample leading to an overestimate of free T4, or analytic with underestimation of the effect of competitors to increase free T4. Current approaches to free T4 measurement are vulnerable to several method-dependent artifacts: abnormal albumin binding of T4 or of the assay tracer, the inhibition of T4 binding to TBG by medications, and the effects of critical illness, especially in heparin-treated patients, pregnancy, and the abnormalities in sick premature infants. Because of systematic variation between methods (i.e., whether a technique is albumin dependent or prone to incubation or dilution artifacts), it is essential to consider methodologic details in evaluating free T4 estimates in these situations and whenever estimates of free T4 are clinically discordant. False-positive abnormalities are more frequent than false-negative results. When free T4 results are correlated with the serum TSH concentration with attention to the assumptions that define this relationship, the majority of false-positive results can be readily identified. If a free T4 anomaly remains unexplained on repeat sampling, it is appropriate to use an alternative free T4 method that depends on a different assay principle and to correlate the result with an authentic total T4 measurement.

Binding of ketoprofen enantiomers in various human albumin preparations

Published data conflict with respect to the enantioselective protein binding parameters of R(-) and S(+) ketoprofen. We studied whether differences in experimental conditions used and/or presence of interfering compounds could provide a possible explanation for these discrepancies. Equilibrium dialysis, supported by ultrafiltration (67 mM Sörensen phosphate buffer pH 7.4, 580 microM HSA, 37 degrees C) allowed the characteristics of the binding sites to be determined according to Scatchard's analysis. (R) and (S)-ketoprofen concentrations were measured by HPLC. The free (R)-ketoprofen/free (S)-ketoprofen (F(R)/F(S)) concentration ratio was calculated. The effect of octanoic acid (OA) found in currently marketed intravenous HSA solutions, and hippuric acid (HA), on F(R)/F(S) concentration ratio was considered. Two classes of binding sites were characterized for both enantiomers. The free (S)-ketoprofen concentrations remained equal to those of the (R)-antipode at low concentrations of racemate (2-35 microg ml(-1)) indicating non-stereoselective albumin binding over the therapeutic range. From 35 microg ml(-1), the free (S)-ketoprofen concentrations were slighty greater than those of its antipode. Both OA and HA induced an increase of the free fraction of the enantiomers by a two-fold to a 15-fold order of magnitude. OA, but not HA, showed a more pronounced effect for the (S)-form leading to a marked decrease in F(R)/F(S) concentration ratio (0.61). Differences in HSA preparations used and/or the presence of interfering compounds may explain the variability in the reported protein binding characteristics of ketoprofen enantiomers.

Misleading serum free thyroxine results during low molecular weight heparin treatment

Measured free thyroxine concentrations in serum increase markedly after intravenous heparin administration, but the effect of heparin administered subcutaneously has not been adequately documented. We found in vitro increases of up to 63% in measured FT4 after a single dose of subcutaneous heparin (enoxaparin, 2000 units) in nine healthy volunteers, and the magnitude of these increases was correlated with initial serum triglyceride concentrations (r = 0.93, P &lt;0.005) and in vitro free fatty acid release (r = 0.88, P &lt;0.005). In 10 cardiac inpatients receiving repeated doses of enoxaparin (2000 units twice daily), measured FT4 increased by up to 171% in specimens taken 2–6 h after injection. When specimens were obtained 10 h after injection, the effect appeared to be minimized, with in vitro increases of &lt;40%, but such increases may still be sufficient to cause interpretative errors. If FT4 estimation is absolutely necessary in patients receiving enoxaparin, specimens should be taken ≥10 h postdose and analyzed within 24 h.