This difference declined with age, dropping to approximately 10% at 70 years of age. 10 One study found young men (30–40 years old) to have average 08.00 testosterone levels (both free and total) that were 30–35% higher than levels measured in the mid- to late afternoon. Peak levels are reached in the morning between 07.00 and 10.00, a trough is seen in the evening and levels then begin to rise again at night. Testosterone secretion has a diurnal pattern of secretion. However, they are useful to consider when interpreting test results alongside factors we regularly take into account, such menstrual cycle phase or menopausal status. These findings are unlikely to alter the time of day we order female reproductive hormone measurements. The hormonal peaks have been found to occur in the morning for progesterone, in the afternoon for FSH and LH, and during the night for oestradiol. In contrast, only FSH is significantly rhythmic during the luteal phase. Oestradiol, progesterone, follicle-stimulating hormone (FSH) and luteinising hormone (LH) show significant 24-hour rhythms during the follicular phase of the menstrual cycle. The fluctuations of female reproductive hormones within a single day are not usually considered when interpreting test results, but these hormones do exhibit endogenous circadian regulation. Thus, the timing of a TSH sample may only be of relevance if treatment decisions are being based on minor changes in TSH level. 7 The circadian differences in secretion may cause a small variation in TSH levels − in older literature a mean of 0.95−2 mIU/l − although generally this does not result in TSH values outside the normal reference range. 6Ī TSH measurement at 09.00 has been shown to strongly correlate with the total 24-hour TSH secretion, sampled at 10-minute intervals. 4,5 Despite this, thyroid hormone levels do not rise significantly after an overnight TSH surge, possibly because overnight TSH molecules are less bioactive than those circulating in the day. TSH concentrations are maximal overnight and lowest in the late afternoon to early evening. Circadian variation in thyroid-stimulating hormone (TSH) levels has been well described, with secretion partially pulsatile and partially basal. The timing of phlebotomy is not usually considered when ordering thyroid function tests. insulin tolerance test or glucagon stress test). 2,3 Given that 5- to 20-minute sampling for 24 hours is not practical, we usually rely on dynamic testing to investigate GH excess (oral glucose tolerance test) or deficiency (e.g. age, sex, weight, sleep, food, stress and exercise) influence the complex regulatory mechanism of the GH axis. Numerous other endogenous and exogenous factors (e.g. Between pulses, the serum GH concentration may be undetectable. Frequent blood-sampling techniques have demonstrated the pulsatile nature of GH secretion, with approximately eight peaks per 24-hour period, predominately at night. Keywords: FT3, FT4, TSH and Diurnal variation.Generally, ordering a random growth hormone (GH) level is unhelpful the results will be difficult to interpret. In our study although statistically significant, all the values are within the normal biological reference interval Further studies in larger cohorts is essential to desire important conclusions. However fluctuations in diurnal variations in thyroid hormone levels are less. The time of blood sampling has an important role in the interpretation of TSH levels. The one sample t test shows difference of FT3, t 4.489 and p value 0.000, FT4, t value 3.092 and p value 0.004 and TSH t value 3.394 and p value 0.002. In our study 36.67% participants were males, 63.3% participants were females. FT4, FT3 and TSH were measured by Enzyme linked immunosorbent assay, using Avantor kit. A total of 60 samples were collected from 30 patients attending KarpagaVinayaga Institute of Medical Sciences at morning (6am-8am) and 2nd sampling at night (8pm-9pm). A cross sectional study was carried out during the March 2019 to September 2019 in patients between 18 years to 60 years. Measuring the concentrations of free thyroid hormones is of great diagnostic value. Abstract : Free thyroxin hormones FT4 and FT3 are unbounded thyroid hormone are biologically active and involves in regulation of metabolism.
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