Free T3 1.4–4.2 pg/mL Methodologic factors and
Total T4 4.4–11.6 µg/dL Binding protein changes, binding
Free T4 0.8–2.0 ng/dL Methodologic factors, pregnancy
Diurnal variation, pulse secretion,
*These ranges should be determined for the particular methods used in each
laboratory. The neonatal period is excluded. Higher values in childhood.
Hormone Reference ranges Variations unrelated to thyroid
Total T3 69–202 ng/dL Binding protein changes, binding
competitors, age-related changes,
nutrition, illness, surgery, drugs
Disease T3 T4 TSH FT3 FT4 T-Uptake Tg Anti-TPO TRH TBG
Primary Hypothyroidism ↓ ↓ ↑ ↓ ↓ ↓ R
Pituitary insuffiency, tertiary hypothroidism ↓ ↓ ↓ ↓ R*
Subacute thyroiditis ↑ ↓ ↑ ↑a , ↓b ↑
Hashimoto thyroiditis ↑ ↑d, ↓e ↑
Androgen therapy, steroid, hypoproteinemia
Hypothyroidism treated with thyroxine ↓
Hypothyroidism treated with Tri-iodothronine ↑
Anti-thyroid drug for thyrotoxicosis ↓, N ↓ ↓
Untreated and metastatic carcinoma of thyroid ↑
Acute psychiatric illness,acute medical illness,
hepatic disease, malnutrition, Addison’s
The four parathyroid glands lie on top of the thyroid gland
in separate nodes spread out to the four quadrants of the
thyroid. Parathyroid hormone is under direct feedback
control of circulating levels of calcium. If calcium levels fall,
then parathyroid hormone is released. As calcium levels rise,
release of the hormone is reduced. Parathyroid hormone
acts on bones, kidneys and intestines to reabsorb calcium.
It includes increased levels of parathyroid hormone. It
is usually rare and occurs as a result of tumor. It leads to
It includes low levels of parathyroid hormone, can result
due to trauma or removal during thyroid surgery.
The production of parathormone varies inversely with
the plasma levels of ionized calcium, which is ordinarily
maintained within normal limits.
Parathormone acts by controling metabolic reactions,
1. Increase calcium and phosphorus reabsorption from
2. Increase calcium reabsorption and phosphate
3. Increase absorption of calcium from the gastrointestinal
4. Decrease calcium secretion in the lactating breast
(secondary hyperparathyroidism may follow renal
peptic ulcer, hypertension, pancreatitis.
The X-ray of the bones of the hands, teeth, and skull,
intravenous urography, serum calcium (repeated), serum
phosphorus, urine calcium, serum alkaline phosphatase,
bone biopsy, calcium and phosphorus tolerance,
reabsorption and excretion tests. Test response of elevated
calcium level to cortisone administration. Reduced blood
of serum calcium is protein bound (while withdrawing
blood, no tourniquet or pressure should be applied). Some
of the important tests are mentioned below:
A finding of serum calcium levels above 11 mg% repeatedly
suggests hyperparathyroidism. Hypercalcemia also occurs
in multiple myeloma, sarcoidosis, milk alkali syndrome,
vitamin-D intoxication, acute osteoporosis, Addison’s
disease, after electroshock therapy, in the presence
of metastatic malignant disease with or without bone
involvement, and in thyrotoxicosis.
On a diet containing about 100 mg of calcium per day,
the normal person excretes 125 ± 50 mg of calcium per
24 hours. If milk or cheese is not present in the diet, the urine
normally forms a slight cloud when Sulkowitch reagent is
added. In hyperparathyroidism, which may be intermittent,
hypercalcemia is usually associated with a daily urinary
excretion of calcium greater than 200 mg. Hypercalcemia
due to this cause is usually unaffected by corticosteroids
(hydrocortisone 100 mg/day, or prednisone 20 mg/day,
for 1 week), which decrease hypercalcemia in sarcoidosis,
infantile hypercalcemia, metastatic malignancy, the usual
case of vitamin-D intoxication, and miliary tuberculosis.
Bone biopsy and tracer studies are diagnostic.
Tubular Reabsorption of Phosphate (TRP)
This test may indicate hyperparathyroidism in patients
with good renal function and a daily phosphate intake of
800 mg or more. False positives may occur with uremia
and in some cases of renal tubular disease, sarcoidosis and
Method: A constant diet containing moderate amounts of
calcium and phosphate is given for 3 days. Fasting blood
is drawn in the morning when a timed 4 hours urine
Urine phosphate (UP) and creatinine (UC) (in mg
excreted/minute) and serum phosphate (SP) and
creatinine (SC) (in mg/100 mL) are determined. Calculate
UP × SC TRP (in%) = 100 × 1 – _________
Interpretation: TRP is about 78% on a normal diet, higher
on a low-phosphate diet (430 mg/day for 3 days). In
hyperparathyroidism, the TRP is 74% or less after a normal
diet, 85% or less on a low-phosphate diet.
Method: On a constant diet, 3 consecutive 24 hours urines
are collected and measured for phosphate. On the second
day, a 4 hours infusion of 1 liter of normal saline solution
containing calcium gluconate-glucoheptonate (in a
quantity enough to provide 15 mg of calcium per kg ideal
Interpretation: A normal response consists of a marked
reduction of urinary phosphate on the day of calcium
infusion and a rebound increase on the third day.
In hyperparathyroidism, minor alteration in urinary
phosphate excretion is observed. Changes in urinary
cyclic AMP parallel phosphate changes.
hormone is adequate, but the renal tubules are unresponsive.
Anaphylactoid reactions to parathyroid extract may occur. Be
sure the extract used is phosphuretic in humans and renal
Method: The fasting patient is given 2 mL (200 units) of
parathyroid extract intravenously. The urinary phosphorus
content is determined hourly for 3 hours prior to and for
3-5 hours following the injection.
Interpretation: Following the injection of parathyroid extract
in normals, there is a 5-fold to 6-fold increase in urine
phosphorus excretion. In hypoparathyroidism, following the
injection of parathyroid extract, there is a 10-fold or greater
cyclic AMP does not increase in proportion.
Radioimmunoassay, ELISA and chemiluminometry methods
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