Table 2.
Effect of levothyroxine (l-T4) on metabolic parameters and laboratory tests
| Reference range for adults | With l-T4 | Off l-T4 | |
|---|---|---|---|
| Weight (kg) | 58.5 | 62.3 | |
| Lean mass (%) | 62 | 62.8 | |
| Fat mass (%) | 36 | 35.8 | |
| Resting energy expenditure (kcal in 24 h) | 1450b | 650 | |
| Respiratory quotienta | 0.7 | 0.88 | |
| Core temperature [mean (sd)] (C) | 37.25 (0.21) | 37.36 (0.19) | |
| TSH (μIU/ml) | 0.4–4.0 | 0.29 | 53.8 |
| Glycated hemoglobin (%) | 4.8–6.4 | 5.5 | 6.7 |
| Glucosefasting (mg/dl) | 70–115 | 94 | 160 |
| Insulinfasting (μU/ml) | 6–27 | 144 | 297 |
| Glucose2-h (mg/dl)c | 320 | 361 | |
| Euglycemic insulin clamp (500 mU · m2 · min−1) | |||
| Glucose infusion rate (mg · kg · min−1) | 3d | ||
| Urinary catecholamines | |||
| Epinephrine (μg in 24 h) | 0–20 | 0 | 3.8 |
| Norepinephrine (μg in 24 h) | 5–80 | 35 | 42 |
To convert the values for glucose to millimoles per liter, multiply by 0.05551; for insulin to picomoles per liter, multiply by 7.217; for TSH to milliunits per liter, multiply by 1; for epinephrine to nanomoles per day, multiply by 5.46; for norepinephrine to nanomoles per day, multiply by 5.91; and for dopamine to nanomoles per day, multiply by 6.53.
The respiratory quotient (RQ) is the ratio of the volume of carbon dioxide produced to the volume of oxygen consumed using indirect calorimetry and reflects the fuel source being metabolized. Under normal physiological conditions, the range of RQ is 0.7 (fat oxidation) to 1.0 (glucose oxidation).
12% greater than the value calculated with the Harris-Benedict equation, which predicts basal energy expenditure using body height, weight, age, and sex.
The glucose measurement was obtained 2 h after the administration of 75 g of glucose orally. Values over 200 mg/dl at the 2-h time point are diagnostic for diabetes mellitus.
Study performed in patient at age 44 yr, after the diagnosis and treatment of thyroid cancer.