Laboratory Tests 1

Initial evaluation of a patient's thyroid status is most commonly done by measuring thryoid stimulating hormone (TSH) concentration in the serum, which is a sensitive indicator of the body's perception of its own thryoid status. In hyperthyroidism, TSH concentration is markedly decreased (the converse is true in hypothyroidism). Usually, serum free T4 will be measured as well and can serve as a confirmatory test for the TSH findings. In some labs, free T4 assay is not routinely available; similar data can be derived from measuring total T4 and T3 resin uptake, and calculating the Free Thyroxine Index (FTI) which is proportional to free T4.

In this patient, there is a nodule associated with the thyroid gland. This finding might result from thyroid pathology but might also indicate a parathyroid adenoma (which would appear in the same area). Thus it is prudent to check the patient's calcium status. Active parathyroid adenomas produce hypercalcemia and may also be associated with marked elevations in circulating alkaline phosphatase (due to active bone resorption).

The test results for this patient were as follows (S = measured in serum):

                          Patient's value   Reference range
Calcium, total (S)           10.6 mg/dl       8.4 - 10.2
Phosphorus                    4.8 mg/dl        2.7 - 4.5
Alkaline phosphatase (S)      160 U/L           49 - 120
T4, Total (S)                12.2 ug/dl         5 - 11.5
T3 resin uptake (S)            35%                25 - 35
T3, Total (S)                 311 ng/dl        100 - 215
TSH (S)                      <0.1 uU/ml         0.7 -7.0
Free thyroxine index (FTI)   14.6               6 - 11.5

Laboratory Tests 1

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