CC_Lab-Finals

• Severely low calcium levels can lead to tetany and altered neuromuscular activity
• Primary Hyperparathyroidism


  1. Most common cause of hypercalcemia

  2. Due to the presence of a functioning parathyroid adenoma

  3. Accompanied with phosphaturia

  4. May lead to severe demineralization if undetected
• Lab Tests - Parathyroid Hormone Immunoassay (PTH) Test


  Measures the level of parathyroid hormone (PTH) in the blood
• Tertiary Hyperparathyroidism

  1. Occurs with secondary hyperparathyroidism

  2. Results in calcium phosphates precipitating in soft tissues
• Parathyroid Gland

  • Located near the thyroid capsule or within the thyroid gland
  • Normal anatomic site is between the hyoid bone in the neck and mediastinum
  • Most people have 4 parathyroid glands
  • Smallest endocrine gland
  • Secretes Parathyroid hormone (PTH)
• Parathyroid hormone interferes with bicarbonate reabsorption in the proximal tubule, leading to increased renal tubular bicarbonate threshold in hypoparathyroidism
• Parathyroid Function

  1. Prevents hypocalcemia by regulating blood calcium

  2. Preserves calcium and phosphate within normal range

  3. Promotes bone resorption to release calcium into the blood stream

  4. Increases renal reabsorption of calcium

  5. Stimulates conversion of inactive Vitamin D to activated vitamin D3

  6. Indirectly stimulates intestinal absorption of calcium

  7. Suppresses PTH secretion as calcium levels increase, allowing urinary loss of calcium and calcium to remain in bone

  8. Releases PTH if calcium levels decrease
• Secondary Hyperparathyroidism

  1. Develops in response to decreased serum calcium

  2. Diffused hyperplasia of all 4 glands

  3. Patient develops severe bone disease

  4. Caused by Vitamin D deficiency and Chronic Renal Failure
• Low calcium levels can lead to laryngeal stridor and tonic-clonic seizures
• Hypoparathyroidism


  1. Caused by accidental injury to parathyroid glands during surgery or autoimmune destruction

  2. Dependent on calcium supplementation
• In hyperparathyroidism, the distal convoluted tubule reabsorbs bicarbonate and phosphate resulting in acidosis
• Clinical Disorders related to Parathyroid

  • Hyperparathyroidism
  • Hypoparathyroidism
• Calcium level < 6 mg/dL (1.5 mmol/L) leads to laryngeal stridor and tonic-clonic seizures
• The best method for PTH measurements involves the use of antibodies that detect both the amino-terminal fragment and intact PTH
• The renal tubular bicarbonate threshold tends to be increased in hypoparathyroidism
• Radioimmunoassay for Serum Immunoreactive Parathyroid Hormone (iPTH) does not recognize amino terminal fragments
• The adrenal cortex produces Aldosterone, Cortisol, and Androgens
• Urine Free Cortisol Measurement (UFC) measures the amount of cortisol in urine
• Causes of increased PTH


  • Hyperparathyroidism
  • Benign tumor of the parathyroid gland
  • Kidney disease
  • Vitamin D deficiency
  • Disorder affecting calcium absorption
• Overnight/Rapid Dexamethasone Suppression Test


  1 mg of dexamethasone orally taken between 11:00pm to 12 midnight, Serum cortisol measured the following day (8:00 AM to 9:00 AM), Urine may be tested for 17-OHCS, Positive results: Cortisol level not suppressed (>5.0 ug/dL), 17-OHCS (>4mg/g Creatinine)
• Reference ranges for PTH: Intact (whole): 10-65 pg/mL or 10-65 ng/L (SI units), N terminal: 8-24 pg/mL, C terminal: 50-330 pg/mL
• The antiserum used in Radioimmunoassay for Serum Immunoreactive Parathyroid Hormone (iPTH) is specific for the carboxy-terminal region of the secreted or intact form of PTH
• Calcium level < 8 mg/dL (2.0 mmol/L) leads to tetany and altered neuromuscular activity (Chvostek’s sign and Trousseau's sign)
• The adrenal medulla consists of Chromaffin cells and produces Norepinephrine, Epinephrine, and Dopamine
• Low PTH causes elevated bicarbonate reabsorption- alkalosis
• Urine Free Cortisol Measurement (UFC)

  24-hour urine collection, avoid alcohol, normal: <2% of cortisol in urine, diagnostic >120 kg/day
• Radioimmunoassay for Serum Immunoreactive Parathyroid Hormone (iPTH) is useful in selective venous catheterization for preoperative localization of hyperfunctioning parathyroid tissue
• The adrenal gland is a pyramid-like shaped gland located on top of the kidneys
• Causes of decreased PTH

  • Hypoparathyroidism
  • Overdose of vitamin D or calcium
• Testes produce androgens (testosterone) and sperm, involved in sexual development
• Testosterone is the most potent male androgen controlled by FSH and LH
• Insulin Tolerance Test

  1. Gold Standard for secondary and tertiary hypocortisolism

  2. Requirement: adequate hypoglycemia must be attained

  3. Oral dose: 0.05 U/kg of insulin

  4. Blood collection at various time points following insulin administration

  5. Normal response: cortisol ≥ 18 ug/L or 20 ug/L at any time during the test
• Tests for male infertility include semen analysis, Testosterone Test, FSH, and LH test
• ACTH Stimulation Test

  1. Cosyntropin test or tetracosactide test

  2. Small amount of synthetic ACTH injected, and cortisol or Aldosterone measured

  3. Dose: 250 ug of Cosyntropin IV or IM

  4. Distinguish cause of adrenal insufficiency or pituitary issue
• Testosterone levels demonstrate a circadian pattern, peaking at 8AM and falling to their lowest level at 8PM
• Gonads are the main source of sex hormones
• Ovaries produce eggs and secrete estrogen, progesterone, and relaxin for sexual development, menstruation, and pregnancy
• Reference value for total testosterone EIA: 3.9-7.9 ng/mL (serum)
• Adrenal Antibody Test

  1. Detects antiadrenal antibodies attacking the body's own adrenal gland in blood

  2. Used to diagnose autoimmune adrenocortical insufficiency

  3. Related test: ACTH

  4. Adults: Negative at 1:10 dilution
• Low-Dose Dexamethasone Suppression Test (LDDST)


  1. 0.5 mg oral dexamethasone given every 6 hours for 2 days

  2. Cortisol measured 15 minutes after the oral dose

  3. 24-hour urine and serum samples collected as specimens