Doctors Lounge - Endocrinology Answers
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Forum Name: Endocrinology Topics
|Cowboy42 - Mon Jul 26, 2010 5:33 pm|
I had two different Drs order blood work. I had the blood work done within a 2 day period of eachother, one fasting, one not fasting.
My TSH, 3rd Generation was 1.91 without fasting (First Test)
My TSH, 3rd Generation 2 days later was 2.53 with fasting. (Second Test 2 days later)
Is this normal? They were both tests from Quest.
My T4 (the 2nd test with fasting) was 11.3
I don't understand why there is such a fluctuation within 2 days of testing?? Does this mean there is a problem w/ my Thyroid? I have Thyroid cancer in my family.
Thank you so much!
|Dr.M.Aroon kamath - Wed Jul 28, 2010 12:06 pm|
This query touches upon two important aspects related to thyroid function testing.
- relationship of TSH levels to food intake and
- timing of the testing.
Firstly, as far as T3 and T4 measurements are concerned, blood may be drawn at any time of the day without fasting. TSH levels also may be measured at any time of the 'day' without the need to fast.
Like other pitutary hormones(such as growth hormone) that show a circadian variation, TSH also shows a fairly consistent pattern of variations during a 24 hour period.
TSH appears to be secreted in a dual fashion,
a) in intermittent pulses(bursts) which constitute 60-70% of the total amount secreted and
b) a background continuous apulsatile(tonic) secretion (30-40%).
The pulses occur roughly every 2-3 hours(subject to variations). Occurrence of these spurts are difficult to pin point accurately.
Several studies indicate that the maximum TSH levels occurs just before a person falls asleep.The levels thereafter tend to maintain during the night, with mean values of 1.34 mu/ml.The serum TSH levels begin to fall the next morning from 8 a.m. to 11 a.m.Thereafter, the level tends to remain low during the rest of the day (mean serum TSH value of 0.85 μU/ml). No relationship between meals and the variation of the TSH level has been noted. The circadian rhythm of serum TSH is not only of physiological interest but has also the practical implications in that, blood sample collections for TSH determinations are best performed at 11 a.m, when the TSH level has fallen to the average daytime levels.
Thus one can appreciate that although TSH,T3 and T4 may be performed at any time of the day and without fasting, there is a valid point in performing TSH testing during the forenoon hours.
You have unfortunately not included your laboratory's normal reference ranges.
Since late 2002, the American Association of Clinical Endocrinologists (AACE) revised the normal range to 0.3-3.0 for serum TSH levels.Prior to 2002, the commonly used range was 0.5-5.0. As explained earlier, TSH levels must not be interpreted in isolation.
You have not mentioned at what time of the day (or night) your blood samples were drawn and whether both times the samples were collected at the same time of the day/night or otherwise. Also, you have not mentioned about having any complaints suggestive of hypothyroidism, i take it that you are perhaps don't have them.Your TSH levels were within normal reference range. But, some endocrinologists would prefer to treat patients with TSH levels >2 if the symptoms and clinical features are so compelling to suggest hypothyroidism.
|Cowboy42 - Wed Jul 28, 2010 12:30 pm|
The blood was drawn at about the same time for both days. About 1 pm.
I go by the new revised Thyroid reference range that you mentioned, not the older ranges. The lab has their reference ranges for TSH set at .4- 4.50 . I have pretty much every symptom of Hypothyroidism but have always been told that I am within range. My TSH before these last two blood tests last week has usually been 3.3 or so. I have weight fluctuations, hair loss, brittle nails, cold, depressed, moody, tired, can't sleep even when tired, etc. I am also living w/ a sinus infection. I know that something is off and have been trying to figure it out. My aunt has thyroid cancer and her Thyroid blood tests came back perfectly normal.
From what you are saying, it is normal for the TSH level to fluctuate day to day and to not be concerned with the number being different in those two tests? Thanks for your help. I appreciate it.
|Dr.M.Aroon kamath - Sun Aug 15, 2010 8:54 pm|
Thank you for the feed back. I urge you to go through the last paragraph of my answer to your first post once again.You had mentioned nothing of the "I have pretty much every symptom of Hypothyroidism" in your first post.
TSH values can not be interpreted in isolation. It is only one of the several factors that have to be considered while interpreting the thyroid function tests.
In general, it may be fair to say that the quality of a reply or the accuracy of a diagnosis will be directly proportional to the quality of the information(history) provided.
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