Davis's Lab & Diagnostic Tests
Thyroid-Stimulating Hormone
General
Synonym/Acronym:
Thyrotropin, TSH. sensitive TSH, third-generation TSH
Rationale
To evaluate thyroid gland function related to the primary cause of hypothyroidism and assess for congenital disorders, tumor, and inflammation. To monitor the effectiveness of thyroid replacement or suppressant therapy.
Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.
Normal Findings
Method: Chemiluminescent Immunoassay.
| Age | Conventional Units | SI Units (Conventional Units × 1) |
|---|---|---|
| Neonates–3 days | Less than 20 micro-international units/mL | Less than 20 milli-international units/L |
| 2 wk–5 mo | 1.7–9.1 micro-international units/mL | 1.7–9.1 milli-international units/L |
| 6 mo–5 yr | 0.7–6.4 micro-international units/mL | 0.7–6.4 milli-international units/L |
| 6 yr–19 yr | 0.5–4.5 micro-international units/mL | 0.5–4.5 milli-international units/L |
| Greater than 20 yr | 0.4–4.2 micro-international units/mL | 0.4–4.2 milli-international units/L |
| Pregnancy | ||
| First trimester | 0.3–2.7 micro-international units/mL | 0.3–2.7 milli-international units/L |
| Second trimester | 0.5–2.7 micro-international units/mL | 0.5–2.7 milli-international units/L |
| Third trimester | 0.4–2.9 micro-international units/mL | 0.4–2.9 milli-international units/L |
Critical Findings and Potential Interventions
N/A
Overview
(Study type: Blood collected in a gold-red- or tiger-top tube; for a neonate, use filter paper; related body system: Endocrine system.)
Thyroid-stimulating hormone (TSH) is produced by the pituitary gland in response to stimulation by thyrotropin-releasing hormone (TRH), a hypothalamic-releasing factor. TRH regulates the release and circulating levels of thyroid hormones in response to variables such as cold, stress, and increased metabolic need. TSH is the preferred test for assessing and monitoring thyroid function; a sensitive or third-generation test method is most commonly used. TSH exhibits diurnal variation, peaking between midnight and 0400, and troughing between 1700 and 1800. TSH values are high at birth but gradually decrease to reach adult levels in the first few years of life. Elevated TSH levels combined with decreased thyroxine (T4) levels indicate hypothyroidism and thyroid gland dysfunction. In general, decreased TSH and T4 levels indicate secondary congenital hypothyroidism and pituitary hypothalamic dysfunction. A normal TSH level and a depressed T4 level may indicate (1) hypothyroidism owing to a genetic defect in T4-binding globulin or (2) transient congenital hypothyroidism owing to hypoxia or prematurity. Early diagnosis and treatment in the neonate are crucial for the prevention of congenital hypothyroidism (cretinism).
Indications
- Assist in the diagnosis of hypothyroidism in the newborn.
- Assist in the diagnosis of hypothyroidism or hyperthyroidism or suspected pituitary (secondary hypothyroidism) or hypothalamic dysfunction (tertiary hypothyroidism).
- Differentiate functional euthyroidism from true hypothyroidism in debilitated individuals.
Interfering Factors
Factors that may alter the results of the study
- Drugs and other substances that may increase TSH levels include amiodarone, antithyroid medications, iodide-containing medications and radiographic medium, lithium, lovastatin, methimazole,metoclopramide, morphine, propranolol, and TRH.
- Drugs and other substances that may decrease TSH levels include acetylsalicylic acid, amiodarone, anabolic steroids, carbamazepine, corticosteroids, glucocorticoids, heparin, and thyroid hormones.
Other Considerations:
- Failure to let the filter paper sample dry may affect test results.
Potential Medical Diagnosis: Clinical Significance of Results
Increased in
A decrease in thyroid hormone levels activates the feedback loop to increase production of TSH.
- Ectopic TSH-producing tumors (lung, breast)
- Hypothyroidism in the neonate (filter paper test)
- Primary hypothyroidism (related to a dysfunctional thyroid gland)
- Secondary hyperthyroidism owing to pituitary hyperactivity
- Thyroid hormone resistance
- Thyroiditis (Hashimoto autoimmune disease)
Decreased in
An increase in thyroid hormone levels activates the feedback loop to decrease production of TSH.
- Excessive thyroid hormone replacement
- Graves disease
- Primary hyperthyroidism (e.g., high thyroxine levels will decrease production of TSH)
- Secondary hypothyroidism (related to pituitary involvement that decreases production of TSH)
- Tertiary hypothyroidism (related to hypothalamic involvement that decreases production of TRH)
Nursing Implications, Nursing Process, Clinical Judgement
Potential Nursing Problems Assessment and Nursing Diagnosis
| Problems | Signs and Symptoms |
|---|---|
| Cardiac output (decreased—related to a deficit of thyroid hormone) | Bradycardia, lethargy, hypotension, decreased thyroid hormone levels, fatigue, activity intolerance, poor peripheral perfusion, cool skin, shortness of breath |
| Nutrition (excess—related to slow metabolism) | Decreased appetite with weight gain; selection of high-calorie, high-sodium foods; sedentary lifestyle; caloric intake greater than metabolic needs; constipation; decreased activity |
| Thought processes (altered—related to decreased cardiac output and impaired cerebral perfusion secondary to a deficit of thyroid hormone) | Altered memory, mental impairment, decreased concentration, depression, inaccurate environmental perception, inappropriate thinking, memory deficits |
Before the Study: Planning and Implementation
Teaching the Patient What to Expect
- Discuss how this test can assist in evaluating thyroid function.
- Explain that a blood sample is needed for the test.
Filter Paper Test (Neonate)
- A newborn screening kit is obtained to complete the testing.
- The heel is cleansed with antiseptic.
- A heel stick is performed by gently squeezing the infant’s heel and touching the filter paper to the puncture site.
- Gauze is used to completely dry the puncture site.
- When collecting samples for newborn screening, it is important to apply each blood drop to the correct side of the filter paper card and fill each circle with a single application of blood.
- Overfilling or underfilling the circles will cause the specimen card to be rejected by the testing facility.
- Testing facility regulations usually require the specimen cards to be submitted within 24 hr of collection.
- Additional information is required on newborn screening cards and may vary by testing facility.
- Newborn screening cards should be allowed to air dry for several hours on a level, nonabsorbent, unenclosed area.
- If multiple patients are tested, do not stack cards.
After the Study: Implementation & Evaluation Potential Nursing Actions
Treatment Considerations
Cardiac Output
- Assess and trend vital signs.
- Monitor and trend thyroid laboratory studies: TSH, T3, T4, and radioactive iodine uptake.
- Assess cardiac status indicators: peripheral pulses; skin color; skin temperature; dry, scaly skin; and periorbital edema.
- Administer ordered thyroid hormone replacement medication.
- Facilitate measures to improve patient warmth: blankets, warm clothing and liquids, and warmer environment.
- Pace activity and schedule rest periods to manage fatigue.
- Use pulse oximetry to monitor oxygen saturation.
- Assess respiratory status checking for crackles and increased respiratory rate, and monitor for fluid overload.
Thought Process
- Promote comprehension and understanding of current events.
- Minimize apprehension and dread.
- Collaborate with the health-care provider (HCP) to manage medical problems associated with decreased cerebral perfusion.
- Provide a modified environment that promotes safety.
- Monitor the ability to provide self-care (activities of daily living), monitor injury risk (violence, fall risk, self-harm risk), and administer ordered thyroid hormone replacement medication.
Nutritional Considerations
- Discuss how to avoid foods with high sodium, saturated fat, and cholesterol content.
- Discuss eating a diet high in protein and low in calories to promote weight loss.
- Encourage eating small, frequent meals to prevent overeating and enhance weight management.
- Encourage the consumption of high-fiber foods such as fruits and vegetables with the skins and whole-grain breads to improve gastric motility.
- Monitor and trend daily weight.
- Accurately assess appetite and measure caloric intake over a 24-hr period.
- Arrange consult with a registered dietitian including cultural considerations in food choices.
Clinical Judgement
- Consider ways to assist caregivers to cope with and manage the effects of mental changes associated with the disease process.
Followup Evaluation and Desired Outcomes
- Understands that depending on the results of this study, additional testing may be performed to monitor disease progression and determine the need for a change in therapy.
