I just did a month of dieting and a week of maintanence calories. I seemed to lose a little fat but the scale didn’t show much. My bloodwork: TSH -1.93, Free T4 - 1.4 (I assume ngdl), Free T3 - 257 (I assume pg/dl). Anyone know whether this is a favorable situation for more fat loss? My TSH last year (when I wasn’t dieting) was 1.68. All this year, my late afternoon body temp’s been low (96.4-98.1) and my hands and feet are cold. I used to always be 98.6. Any help would be appreciated.
The reference ranges we use at the hospital I work at are as follows (however, you will see this vary from hospital to hospital - they are not standardized values):
- FREE T4: 0.7 to 2.0
- FREE T3: 2.3 to 4.2
- TSH: above 2.0
The levels of circulating thyroid hormones that are “normal” for any given individual may vary tremendously, however. For example, one subject may have a normal level of Free T4 at the upper end of the normal range, and a slight decrease in this Free T4 may cause an increase in TSH, despite still “high normal” levels of Free T4. Conversely, another individual may have a “normal” Free T4 at the lower end of the range, and even a slight increase in this persons level of circulating thyroid hormones may be associated with mild hyperthyroidism and a suppressed TSH. Hence, one needs to individualize each persons range of normal circulating thyroid hormones, and look at the laboratory limits of what is normal for a large population in this context.
T4 evaluation (Murphy-Pattee Test) offers somewhat more reliability in thyroid evaluations than T3, since the T3 uptake is affected by a variety of exogenous influences such as drugs, estrogens, etc. The serum thyroxine study is a direct measurement of the total amount of thyroxine bound to plasma protein.
This is a very reliable test of thyroid function; however, results are affected by thyroid-binding globulin (TBG). Because T4 is bound by serum proteins such as TBG, any increase in these proteins (as in pregnant women and patients taking oral contraceptives) will cause fictitiously elevated levels of T4 and, to some extent, triiodothyronine (T3).
Therefore, levels of these carrier proteins are concomitantly measured by T3 resin uptake studies, and T3 resin results must be considered when interpreting the T4 test results. Obviously, high levels indicate hyperthyroid states and low levels indicate hypothyroid states.
What you could do is calculate T7 for an accurate interpretation seeing that you are trying to figure out if you can “lose more weight”
This mathematical calculation is made by combining T3 and T4 in the following formula:
T3 x T4 divided by 100 = T7
Thus, if the T3 is 20% (low side of normal) due to some drug influence and the T4 is 12 mg/ml (high side of normal), the T7 calculation becomes:
20% x 12 mg = 2.4 mg T7
A 2.4 mg T7 is well within the normal range of 0.85 - 3.92 mg/ml, and the patient presents a probable normal thyroid.