Plasma free thyroxine (FT4) concentrations during hemodialysis in patients with chronic renal failure: effects of plasma non-esterified fatty acids on FT4 measurement

Hypothyroidism and reversible kidney dysfunction: an essential relationship to recognize

OBJECTIVE

To report 3 cases of reversible hypothyroidism-induced kidney dysfunction and review the interaction between these commonly encountered, yet seemingly disparate, conditions.

METHODS

We describe the clinical course and laboratory and physical findings of 3 patients who presented with kidney dysfunction that improved after initiating thyroid hormone replacement therapy. We also review similar cases in the literature and discuss the pathophysiologic mechanisms.

RESULTS

A 68-year-old male presented with classical signs and symptoms of hypothyroidism, including fatigue, confusion, and gait imbalance. Physical exam showed bradycardia, thyromegaly, slow mentation, and cracked, thin skin; he was found to have decreased kidney function. Second, a 42-year-old previously healthy female presented with bilateral hand swelling and elevated serum creatinine with an otherwise unremarkable physical exam. The third patient was a 72-year-old male with advanced heart failure on amiodarone and stage 3 chronic kidney disease who presented with fatigue, acute kidney injury, and lower extremity edema. In all cases, serum creatinine and thyroid-stimulating hormone (TSH) were elevated at presentation (1.4-3.0 mg/dL and 94.1-184 mIU/L respectively), and free thyroxine (T4) was low (undetectable-0.4 ng/dL). The initiation or increased dose of levothyroxine normalized serum creatinine to baseline within 2 to 10 months.

CONCLUSION

Hypothyroidism and kidney dysfunction are both commonly encountered clinical entities, but the interplay between the thyroid gland and kidneys may be infrequently recalled, causing the reversible relationship between these 2 disorders to be missed.

Sudden cardiac death and diabetes mellitus

Sudden cardiac death (SCD) affects a significant percentage of diabetic patients. SCD in these patients can be due to several factors, such as diastolic dysfunction, heart failure, altered platelet function, inflammation, sympathetic nervous stimulation and other factors. In the present review, we discuss the association between diabetes mellitus and SCD.

The expanding role of tandem mass spectrometry in optimizing diagnosis and treatment of thyroid disease

This review discusses the state-of-the-art measurement of free and total thyroid hormones in clinical laboratories. We highlight some of the limitations of currently used immunoassays and critically discuss physical separation methods for the measurement of free thyroid hormone. Physical separation methods, such as equilibrium dialysis or ultrafiltration, followed by tandem mass spectrometry for the measurement of free thyroid hormones offer many advantages, which we feel, can deepen our understanding of thyroid hormone metabolism and improve patient diagnosis and care. Problems with direct analogue immunoassay methods for FT4/FT3 as well as immunoassay methods for total T3 at low T3 concentrations and during pregnancy are highlighted. Improved diagnosis and patient management can be achieved utilizing tandem mass spectrometry for these measurements.

Metabolite profiling identifies markers of uremia

ESRD is a state of small-molecule disarray. We applied liquid chromatography/tandem mass spectrometry-based metabolite profiling to survey>350 small molecules in 44 fasting subjects with ESRD, before and after hemodialysis, and in 10 age-matched, at-risk fasting control subjects. At baseline, increased levels of polar analytes and decreased levels of lipid analytes characterized uremic plasma. In addition to confirming the elevation of numerous previously identified uremic toxins, we identified several additional markers of ESRD, including dicarboxylic acids (adipate, malonate, methylmalonate, and maleate), biogenic amines, nucleotide derivatives, phenols, and sphingomyelins. The pattern of lipids was notable for a universal decrease in lower-molecular-weight triacylglycerols, and an increase in several intermediate-molecular-weight triacylglycerols in ESRD compared with controls; standard measurement of total triglycerides obscured this heterogeneity. These observations suggest disturbed triglyceride catabolism and/or beta-oxidation in ESRD. As expected, the hemodialysis procedure was associated with significant decreases in most polar analytes. Unexpected increases in several metabolites, however, indicated activation of a broad catabolic program, including glycolysis, lipolysis, ketosis, and nucleotide breakdown. In summary, this study demonstrates the application of metabolite profiling to identify markers of ESRD, provide perspective on uremic dyslipidemia, and broaden our understanding of the biochemical effects of hemodialysis.

Clinical evaluation of nine free thyroxine assays: persistent problems in particular populations

Over the past decade, numerous papers have addressed the various methodological problems encountered with free thyroxine (FT4) assays. We evaluated the clinical performance of nine FT4 assays in five centres, using a panel of 310 sera: 156 from euthyroid controls; 27 from hyperthyroid patients; 34 from untreated hypothyroidism; 22 from patients with renal failure; 30 from women in the last trimester of pregnancy; 23 from patients on thyroid substitutive therapy; and 18 from patients treated with amiodarone. Only three methods showed a Gaussian distribution of FT4 concentrations. Reference ranges were calculated using the 2.5th and 97.5th percentiles. A significant difference was observed between FT4 values in men and women. The areas under the receiver operating characteristic (ROC) curves ranged from 0.996 to 1 for hyperthyroidism and from 0.973 to 1 for hypothyroidism. In sera from patients with renal failure and from pregnant women, method-dependent biases were observed and confirmed with dilution experiments. In conclusion, current FT4 assays show good performance regarding the diagnosis of overt dysthyroidism. Nevertheless, FT4 measurements are still vulnerable to method-dependent artefacts in particular populations such as patients with renal failure and pregnant women.

Effects of neutering on hormonal concentrations and energy requirements in male and female cats

OBJECTIVE

To determine whether changes in concentrations of hormones involved in glucose and fatty acid homeostasis are responsible for the increased probability that neutered cats will develop obesity and diabetes mellitus.

ANIMALS

10 male and 10 female weight-maintained adult cats.

PROCEDURE

Results of glucose tolerance tests and concentrations of hormones and nonesterified fatty acids (NEFA) were examined before and 4, 8, and 16 weeks after neutering.

RESULTS

Caloric requirements for weight maintenance were significantly decreased 8 and 16 weeks after neutering in females. Glucose concentrations during a glucose tolerance test did not change in neutered females or males. The area under the curve (AUC) for insulin was significantly higher in males, compared with females, before neutering. However, the AUC for insulin increased and was significantly higher 4 and 8 weeks after neutering in females. The AUC for insulin did not change in neutered male cats. Leptin concentrations did not change in females but increased significantly in males 8 and 16 weeks after neutering. Thyroxine concentrations did not change after neutering; however, free thyroxine concentration was significantly higher in females than males before neutering. Baseline concentrations of NEFA were significantly higher in female than male cats before but not after neutering. Suppression of NEFA concentrations after glucose administration decreased successively in male cats after neutering, suggesting decreased insulin sensitivity.

CONCLUSIONS AND CLINICAL RELEVANCE

Changes in NEFA suppression, caloric intake, and leptin concentrations may be indicators of, and possible risk factors for, the development of obesity in cats after neutering.