Long-term stability of thyroid hormones and DNA in blood spots kept under varying storage conditions

Serum Total Thyroxine Evaluation in Critically Ill Feline Patients

This retrospective case control study compared serum total thyroxine (tT4) concentrations in hospitalized critical cats (CCs) and non-hospitalized cats with non-thyroidal chronic diseases (chronic group, CG) and evaluated the relationship between the serum tT4 concentration of CCs and systemic inflammation (systemic inflammatory response syndrome (SIRS)), disease severity (Acute Patient Physiologic and Laboratory Evaluation (APPLEfast)), and prognosis. Cats with previously suspected or diagnosed thyroid disease were excluded. Serum tT4 was evaluated in surplus serum samples at the time of admission for CCs and CGs. The APPLEfast score of the CC group was calculated at admission. The systemic inflammatory response syndrome (SIRS) in CCs was determined using proposed criteria. Cats were divided into survivors and non-survivors according to the discharge outcome. Forty-nine cats were retrospectively included. Twenty-seven cats died during hospitalization. The CG group was composed of 37 cats. The CC group showed a significantly lower tT4 compared to the CG group (1.3 ± 0.7 vs. 2 ± 0.9; p < 0.0001). Among SIRS, APPLEfast, and tT4, only tT4 was associated with mortality (p = 0.04). The tT4 cut-off point for mortality was 1.65 μg/dL (sensitivity 81%, specificity 57%, odds ratio (OR) 5.6). Twenty-five cats (51%) had SIRS that was not associated with tT4. Non-thyroidal illness syndrome can occur in critically ill cats and the evaluation of tT4 in hospitalized cats could add prognostic information.

Comparison of 2 assays for measuring serum total thyroxine concentration in dogs and cats

Background

No gold standard assay for serum total thyroxine (TT4) concentration in small animals exists. The Microgenics DRI TT4 (MTT4) assay is used by most reference laboratories.

Hypothesis/Objectives

IDEXX Catalyst Total T4 (CTT4) and Immulite 2000 TT4 (ITT4) results will agree with MTT4 results.

Animals

Residual small animal sera were randomized before reanalysis (dogs, CTT4 versus MTT4: n = 176, ITT4 versus MTT4: n = 74; cats, CTT4 versus MTT4: n = 319, ITT4 versus MTT4: n = 79).

Methods

Validation and method comparison study. Serum TT4 concentration was measured on all analyzers. Pairwise Pearson correlation, cumulative sum linearity test, regression, and Bland‐Altman method were performed.

Results

CTT4 versus MTT4 in dogs: constant bias (y‐intercept) was 0.10 μg/dL (95% confidence interval [CI], 0.05‐0.15), proportional bias (slope) was 0.86 μg/dL (95% CI, 0.83‐0.89); in cats, constant bias was 0.13 μg/dL (95% CI, 0.08‐0.20) and proportional bias was 1.01 μg/dL (95% CI, 0.98‐1.03), but the test for linearity failed. Bland‐Altman plots identified increasing disagreement with increasing serum TT4 concentrations.

ITT4 versus MTT4 in dogs, constant bias was 0.14 μg/dL (95% CI, 0.04‐0.22) and 0.22 μg/dL (95% CI, 0.09‐0.33) for cats; proportional bias was 0.76 (95% CI, 0.72‐0.80) for dogs and 0.71 (95% CI, 0.69‐0.74) for cats.

Conclusions and Clinical Importance

Differences in CTT4 and MTT4 results affect interpretation at higher serum TT4 concentrations. The ITT4 proportional bias will underestimate serum TT4 concentrations in dogs and cats, compared to MTT4. Serial TT4 measurements should be done using the same assay.

Cortisol, progesterone, 17α-hydroxyprogesterone, and TSH responses in dogs injected with low-dose lipopolysaccharide

Background

Stress and diseases such as endotoxemia induce cortisol synthesis through a complex biosynthetic pathway involving intermediates (progesterone, and 17α-hydroxyprogesterone (17α-OHP)) and suppression of the hypothalamus-pituitary-thyroid axis.

Objective

To measure plasma concentrations of cortisol, progesterone, 17α-OHP, and thyroid stimulating hormone (TSH) in dogs experimentally injected with intravenous low-dose lipopolysaccharide (LPS). Our hypothesis was that LPS treatment would elicit a significant increase in cortisol and its precursors, and a significant decrease in TSH concentration.

Methods

Hormone measurements were performed on blood samples left over from a previous investigation (2011) on the effect of low-dose LPS on hematological measurands. Five sexually intact female dogs, none in estrous at the time of the study, were administered saline treatment two weeks prior to LPS treatment. LPS was administered intravenously at a dose of 0.1 µg/kg. Blood was collected before (baseline, time -24 hours) and 3-, 6- and 24-hours post-injection. Mixed model analysis for repeated measures was used, with both treatment and time as the repeated factors. Ranked transformation were applied when diagnostic analysis exhibited violation of normality and equal variance assumptions. Post hoc multiple comparisons were performed with Tukey’s adjustment. Statistical significance was defined as p < 0.05.

Results

Significant differences relative to baseline values were detected following both treatments. Compared to baseline, dogs had significantly higher cortisol and 17α-OHP at 3-hours, and significantly lower TSH at 3- and 6-hours following LPS treatment. Dogs had significantly lower TSH at 6- and 24- following saline treatment. Though not statistically significant, the trend in progesterone concentrations was similar to cortisol and 17α-OHP, with an increase at 3-hours post-injection followed by a decrease close to baseline following both LPS and saline. Cortisol and 17α-OHP concentrations were higher after LPS treatment than after saline treatment at 3- and 6-hours post-injection, but differences were not statistically significant, and no significant differences between treatments were detected for any other hormone or timepoint.

Discussion and conclusion

Cortisol and its adrenal precursors are released in the bloodstream following a low dose of LPS, while TSH appears to decrease. Similar changes occurred following saline treatment, suggesting that even routine handling and saline injection in conditioned dogs can elicit alterations in the internal equilibrium with subsequent modification of both hypothalamus-pituitary-adrenal and thyroid axes. Changes to adrenal and thyroid hormone concentrations must be interpreted in light of clinical information. Further studies are needed to elucidate mechanisms of adrenal steroidal hormone synthesis and secretion in response to various stressful stimuli in both neutered and intact animals.

Effects of drying and storage conditions on the stability of TSH in blood spots

OBJECTIVE

To evaluate the influence of sample drying and storage temperature on TSH stability in neonatal screening.

SUBJECTS AND METHODS

Blood samples from 29 adult volunteers as a surrogate for neonatal blood (10 with normal TSH, 9 with overt hypothyroid and 10 with subclinical hypothyroidism) were spotted on filter paper and dried at 22°C or 35°C for 3 hours. The samples were then stored at 22°C, -4°C, or -20°C, and TSH measurements were performed at day 0 (D0), D7, D30, D60, D180, and D360 of storage.

RESULTS

The drying temperature did not interfere with TSH measurement on D0. TSH values remained stable up to D30 when stored at 22°C and were stable up to D60 when stored in a refrigerator or freezer. Samples stored at 22°C had a greater decrease in TSH values than samples stored in a refrigerator or a freezer.

CONCLUSIONS

Freezer storage is not advantageous compared to storage in the refrigerator. At the end of one year, if confirmation of the initial result is required, a reduction of TSH concentrations should be taken into account.

Lithium in drinking water and thyroid function

BACKGROUND

High concentrations of lithium in drinking water were previously discovered in the Argentinean Andes Mountains. Lithium is used worldwide for treatment of bipolar disorder and treatment-resistant depression. One known side effect is altered thyroid function.

OBJECTIVES

We assessed associations between exposure to lithium from drinking water and other environmental sources and thyroid function.

METHODS

Women (n=202) were recruited in four Andean villages in northern Argentina. Lithium exposure was assessed based on concentrations in spot urine samples, measured by inductively coupled plasma mass spectrometry. Thyroid function was evaluated by plasma free thyroxine (T4) and pituitary gland thyroid-stimulating hormone (TSH), analyzed by routine immunometric methods.

RESULTS

The median urinary lithium concentration was 3,910 μg/L (5th, 95th percentiles, 270 μg/L, 10,400 μg/L). Median plasma concentrations (5th, 95th percentiles) of T4 and TSH were 17 pmol/L (13 pmol/L, 21 pmol/L) and 1.9 mIU/L, (0.68 mIU/L, 4.9 mIU/L), respectively. Urine lithium was inversely associated with T4 [β for a 1,000-μg/L increase=-0.19; 95% confidence interval (CI), -0.31 to -0.068; p=0.002] and positively associated with TSH (β=0.096; 95% CI, 0.033 to 0.16; p=0.003). Both associations persisted after adjustment (for T4, β=-0.17; 95% CI, -0.32 to -0.015; p=0.032; for TSH: β=0.089; 95% CI, 0.024 to 0.15; p=0.007). Urine selenium was positively associated with T4 (adjusted T4 for a 1 μg/L increase: β=0.041; 95% CI, 0.012 to 0.071; p=0.006).

CONCLUSIONS

Exposure to lithium via drinking water and other environmental sources may affect thyroid function, consistent with known side effects of medical treatment with lithium. This stresses the need to screen for lithium in all drinking water sources.