Type of test Blood

Normal findings

 Free T4 :

 0-4 days: 2-6 ng/dL or 26-68 pmol/L (SI units)

 2 weeks-20 years: 0.8-2 ng/dL or 10-26 pmol/L (SI units)

 Adult: 0.8-2.8 ng/dL or 10-36 pmol/L (SI units)

 Total T4 :

1-3 days: 11-22 mcg/dL or 152-292 nmol/L (SI units)

 1-2 weeks: 10-16 mcg/dL or 126-214 nmol/L (SI units)

 1-12 months: 8-16 mcg/dL or 101-213 nmol/L (SI units)

 1-5 years: 7-15 mcg/dL or 94-194 nmol/L (SI units)

 5-10 years: 6-13 mcg/dL or 83-172 nmol/L (SI units)

10-15 years: 5-12 mcg/dL or 72-151 nmol/L (SI units)

 Adult male: 4-12 mcg/dL or 59-135 nmol/L (SI units)

 Adult female: 5-12 mcg/dL or 71-142 nmol/L (SI units)

Adult > 60 years: 5-11 mcg/dL or 64-142 nmol/L (SI units)

 Pregnancy: 9-14 mcg/dL or 117-181 nmol/L (SI units)

 Test explanation and related physiology

 The two main hormones secreted by the thyroid gland are thyroxine, which contains four atoms of T4 and T3. More than 90% of thyroid hormone is made up of T4 . Thyroid hormones circulate primarily bound to carrier proteins (e.g., TBG, albumin, or transthyretin); a small fraction circulates unbound (free). Only the free forms are metabolically active. Ninety-nine percent of T4 is bound to proteins. Total T4 measurements consist of both the bound and unbound fractions. Free T4 is a measure of unbound metabolically active T4 . Thyroxine tests are used to determine thyroid function. Greater than normal levels indicate hyperthyroid states, and subnormal values are seen in hypothyroid states. T4 and TSH are used to monitor thyroid replacement and suppressive therapy.

Abnormalities in protein levels can have a significant effect on the results of the total T4 . Pregnancy and hormone replacement therapy increase TBG and may cause total T4 to be falsely elevated, suggesting that hyperthyroidism exists when in fact the patient is euthyroid. If the free T4 is measured in these patients, it would be normal, indicating that free T4 is a more accurate indicator of thyroid function than total T4 . In cases in which TBG is reduced (e.g., hypoproteinemia), the total T4 is likewise reduced, suggesting hypothyroidism. Measurement of free T4 would indicate normal levels and thereby discount the abnormal total T4 as merely a result of the reduced TBG and not as a result of hypothyroidism.

Interfering factors

 • Neonates have higher free T4 levels than older children and adults.

 • Pregnancy causes increased total T4 levels.

* Drugs that increase free T4 levels include aspirin, danazol, heparin, and propranolol.

* Drugs that decrease free T4 levels include furosemide, methadone, phenytoins, and rifampicin. Exogenously administered thyroxine causes increased free T4.

* Drugs that may cause increased total T4 levels include clofibrate, estrogens, heroin, methadone, and oral contraceptives.

* Drugs that may cause decreased T4 levels include anabolic steroids, androgens, antithyroid drugs (e.g., propylthiouracil), lithium, phenytoin, and propranolol.

Procedure and patient care

 • See inside front cover for Routine Blood Testing.

 • Fasting: no

 • Blood tube commonly used: red

• Evaluate the patient’s medication history.

* If indicated, instruct the patient to stop exogenous T4 medication 1 month before testing.

 • List on the laboratory slip any drugs that may affect test results.

Abnormal findings

Increased levels

- Graves disease

- Toxic thyroid adenoma

- Acute thyroiditis

- Familial dysalbuminemic hyperthyroxinemia

- Factitious hyperthyroidism

- Struma ovarii

- Pregnancy

- Hepatitis

- Congenital hyperproteinemia

- Thyroid cancer

- Toxic multinodular goiter

Decreased levels

- Congenital hypothyroidism

- Surgical ablation of the thyroid

- Myxedema

- Pituitary insufficiency

- Hypothalamic failure

- Iodine insufficiency

- Renal failure

- Cushing syndrome

- Cirrhosis

- Hashimoto thyroiditis

- Thyroid agenesis

- TSH receptor defects

اخر الاخبار

اخبار العتبة العباسية المقدسة

وفد العتبة العباسية المقدسة يجري جولة في أروقة معرض بغداد الدولي للكتاب

شعبة التوجيه الديني النسوي تطلق برنامجًا قرآنيًّا لزائرات مرقد أبي الفضل العباس (عليه السلام)

جامعة الكفيل تطلق دورة تدريبية عن تقييم الأداء الجامعي لعدد من ملاكاتها

المجمع العلمي يقيم محفلًا قرآنيًا بذكرى ولادة الصادقين (صلوات الله عليهما)

المزيد

الآخبار الصحية

هل يتنبأ الذكاء الاصطناعي بأمراضنا قبل حدوثها؟

وداعا للنظارات.. قطرة عين واحدة قد تغير كل شيء ؟

دراسة تكشف تأثير "تيك توك" وتطبيقات الفيديو على سلوك الأطفال

"أسرار خفية" في الشاي الأخضر.. تغير قواعد الصحة والوزن

المزيد

الآخبار التكنلوجية

أول قطار يعمل بالهيدروجين في أميركا يدخل الخدمة رسميًا

أجهزة أبل القادمة.. "حصن منيع" في عصر الهجمات الرقمية !

روسيا: تطلق قمرين اصطناعيين بواسطة الصاروخ سويوز 2.1

ميزة ثورية.. أبل تدخل عالم قياس ضغط الدم

المزيد

مواضيع ذات صلة

thyroid-stimulating immunoglobulins

thyroid-stimulating hormone stimulation test (TSH stimulation test)

Disorders of ADH secretion and action

Antidiuretic Hormone

Prolactin

thyroid-stimulating hormone (TSH, Thyrotropin, TRH stimulation test)

thyroglobulin (Tg, Thyrogen-stimulated thyroglobulin)

thrombosis indicators

Laboratory Investigations of Growth Hormone

Growth Hormone Deficiency

Laboratory Diagnosis of Thrombophilia

thromboelastography (Thromboelastometry)