Thyroid hormone therapy monitoring

Thyroid hormone replacement therapy in patients with diabetes may increase the intensity of the symptoms or the diabetes. The nurse closely monitors the patient with diabetes during thyroid hormone replacement therapy for signs of hyperglycemia (see Chap. 49) and notifies the primary health care provider if this problem occurs. 

Treatment is thyroid hormone replacement. The goal of the therapy is to relieve the symptoms of hypothyroidism by normalizing the levels of circulating thyroid hormones. In addition to the amelioration of symptoms, the clinical effectiveness of the thyroid hormone replacement may be monitored by periodically measuring the serum TSH concentration. The lowest dose of thyroid hormone that is needed to normalize the serum TSH concentration is usually the appropriate dose. Most or all of the symptoms of hypothyroidism should improve with appropriate thyroid hormone replacement, but this may require weeks or months of therapy. 

Subclinical hypothyroidism, defined as an elevated TSH level and normal thyroid hormone levels, is found in 4-10% of the general population but increases to 20% in women older than age 50. The consensus of expert thyroid organizations concluded that thyroid hormone therapy should be considered for patients with TSH levels greater than 10 mlU/L while close TSH monitoring is appropriate for those with lower TSH elevations. 

Treatment with thyroid hormones therefore poses only a few essential questions which dosage should be used, which formulation should be chosen, and how can therapy best be monitored so as to avoid short-term and long-term risks. 

Prolonged therapy with methadone causes increases in serum thyroid hormone-binding globulin, triiodothyronine, and thyroxine, as well as albumin, globulin, and prolactin, and these must be monitored (SEDA-15, 71 SEDA-17, 81). 

A horse receiving thyroid supplementation should have its serum T4 and T3 values monitored every 4-6 weeks and the dosage of the supplement should be adjusted to maintain serum concentrations of thyroid hormone within the reference range. If therapy is discontinued, the horse should be weaned slowly from the medication to allow its thyroid tissue function time to return to normal. 

The rise in body temperature during peroxide therapy undoubtedly reflects stimulation of the thyroid gland, as well as stimulation of the immune system. We monitor the effectiveness of thyroid hormone by periodically checking the body temperature. As the thyroid starts working, the temperature slowly rises. It usually takes about eight weeks to see the effect and measure a temperature rise of a few tenths of a degree. 

Fig. 3 Biochemical monitoring of a patient during treatment for thyroid disease. This 55-year-old woman was first diagnosed as hyperthyroid, and received radioiodine therapy. She became profoundly hypothyroid, and was treated with thyroxine. Her thyroid hormone results at first indicated good replacement, but recently they indicate that she Is under replaced. It is possible that she Is not taking her thyroxine tablets regularly.

Therapy with levothyroxine is very safe, provided that thyroid hormone levels are monitored and maintained within the normal range. Excess doses of T4 are associated with a loss of bone mass. A meta-analysis of 41 controlled studies on the impact of thyroid hormone therapy on bone mineral density (Uzzan et al., 1996) has shown that doses of T4 that suppress thyrotropin (TSH) secretion are associated with a significant loss of bone in the lumbar spine and hip in postmenopausal women. Another review of the evidence of the thyroid hormone effect of on skeletal integrity concluded that hyperthyroidism and the use of thyroid hormone to suppress TSH seem to have an adverse effect on bone, especially in postmenopausal women (Greenspan and Greenspan, 1999) however, thyroid hormone replacement seems to have a minimal effect on bone. 

Three main modalities of therapy should be considered for patients with thyrotoxicosis, namely, medical therapy, surgical thyroidectomy, and radioiodine. The choice between these therapies should be dictated by the clinical nature of the disease, the patient s general health, her desire for pregnancy or need to care for young children, and overall patient preference. Treatment is initially monitored by free thyroxine (T4) values, as suppression of thyroid-stimulating hormone (TSH) may persist for months despite adequate management. 

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