Unit Converter
Parathyroid hormone (PTH)
Synonyms
- Parathyroid hormone
- PTH
- Intact PTH (iPTH)
- Bio-intact PTH (1–84 PTH)
- Parathormone
- Parathyrin
Units of Measurement
- pmol/L
- pg/mL
- pg/dL
- pg/100 mL
- pg%
- pg/L
- ng/L
Molecular Weight
~9500 Da (9.5 kDa) for intact 1–84 PTH.
Unit Conversions
pg/mL ↔ pmol/L
For intact PTH (MW ≈ 9500 g/mol):
1 pg/mL=0.105 pmol/L1\ \text{pg/mL} = 0.105\ \text{pmol/L}1 pg/mL=0.105 pmol/L 1 pmol/L=9.5 pg/mL1\ \text{pmol/L} = 9.5\ \text{pg/mL}1 pmol/L=9.5 pg/mL
pg/mL ↔ pg/dL
1 pg/mL=100 pg/dL1\ \text{pg/mL} = 100\ \text{pg/dL}1 pg/mL=100 pg/dL
pg/mL ↔ pg/L
1 pg/mL=1000 pg/L1\ \text{pg/mL} = 1000\ \text{pg/L}1 pg/mL=1000 pg/L
ng/L
1 ng/L=1 pg/mL1\ \text{ng/L} = 1\ \text{pg/mL}1 ng/L=1 pg/mL
pg%
Same as pg/dL.
Description
Parathyroid hormone (PTH) is an 84-amino-acid peptide hormone secreted by the parathyroid glands in response to hypocalcemia.
PTH increases serum calcium by:
- Increasing bone resorption
- Enhancing renal calcium reabsorption
- Increasing renal phosphate excretion
- Stimulating calcitriol (1,25-OH₂D₃) production → ↑ intestinal calcium absorption
PTH secretion is tightly regulated via:
- Calcium-sensing receptor (CaSR)
- Vitamin D levels
- Serum phosphate
Most clinical laboratories measure intact PTH (1–84) using 2nd-generation immunoassays.
Physiological Role
PTH maintains calcium–phosphate balance essential for:
- Bone remodeling
- Neuromuscular function
- Cardiac contractility
- Hormonal secretion
It works in coordination with vitamin D and calcitonin.
Clinical Significance
HIGH PTH (Hyperparathyroidism)
1. Primary Hyperparathyroidism (PHPT)
Cause: adenoma (85%), hyperplasia, carcinoma.
Findings:
- High PTH
- High calcium
- Low phosphate
- High urinary calcium
2. Secondary Hyperparathyroidism
Due to:
- Chronic kidney disease (CKD)
- Vitamin D deficiency
- Malabsorption
- Low calcium intake
- Severe liver disease
- Hyperphosphatemia
- Long-standing hypocalcemia
3. Tertiary Hyperparathyroidism
Autonomous PTH secretion in long-term CKD.
4. PTH-dependent Hypercalcemia
- Familial hypocalciuric hypercalcemia (FHH)
- Drugs: lithium, thiazides
5. Bone Disorders
- Osteomalacia
- Rickets
- Severe osteoporosis
6. Acute or Chronic Hypocalcemia
PTH increases to restore calcium levels.
LOW PTH (Hypoparathyroidism)
1. Postsurgical Hypoparathyroidism
Most common cause:
- Thyroidectomy
- Parathyroidectomy
- Neck surgery
2. Autoimmune Hypoparathyroidism
Part of APECED syndrome.
3. Hypomagnesemia
Mg deficiency blocks PTH secretion.
4. Infiltrative Diseases
- Hemochromatosis
- Wilson disease
- Granulomatous disease
5. Genetic Disorders
- CaSR activating mutations
- DiGeorge syndrome (22q11 deletion)
6. Severe Hypercalcemia
Suppresses PTH secretion.
Reference Intervals
(Tietz 8E + Mayo + ARUP + KDIGO CKD-MBD)
Ranges vary with assay; typical estimates:
Intact PTH (1–84) - Adults
- 15 – 65 pg/mL
(= 1.6 – 6.9 pmol/L)
Children
Often slightly higher.
CKD-specific Targets (KDIGO 2017)
For CKD stage 3–5 (not on dialysis):
- Maintain PTH in normal range, avoid both high & low extremes.
For CKD stage 5D (dialysis):
- Target: 2–9 × upper limit of normal
(example if ULN = 65 pg/mL → 130–585 pg/mL)
Diagnostic Uses
1. Hyperparathyroidism Evaluation
- Primary, secondary, tertiary
- PTH–calcium combination gives diagnosis
2. Hypocalcemia Workup
Low Ca + high PTH → secondary hyperparathyroidism
Low Ca + low PTH → hypoparathyroidism
3. Chronic Kidney Disease (CKD–MBD)
Monitor mineral bone disorder.
4. Vitamin D Deficiency
PTH increases before calcium falls.
5. Osteoporosis
High PTH = high turnover bone loss.
6. Postoperative Monitoring
Predicts postoperative hypocalcemia after thyroid surgery.
Analytical Notes
- Sample: serum or EDTA plasma
- Avoid prolonged tourniquet (false increase)
- Process quickly or refrigerate
- Hemolysis minimally affects assay
- PTH is unstable at room temperature - freeze if delayed
- Third-generation assays (bio-intact PTH) available for research
Clinical Pearls
- PTH should always be interpreted with calcium, phosphate, and vitamin D.
- High PTH + high Ca = primary hyperparathyroidism.
- High PTH + low Ca = secondary hyperparathyroidism.
- Low PTH + low Ca = hypoparathyroidism → treat urgently if tetany occurs.
- CKD elevates PTH due to phosphate retention & low vitamin D.
- Thiazides increase calcium → may cause mild PTH elevation.
Interesting Fact
PTH secretion is controlled by the calcium-sensing receptor (CaSR) - one of the most sensitive and elegant homeostatic systems in human physiology.
References
- Tietz Clinical Chemistry & Molecular Diagnostics, 8th Edition - Endocrine Tests
- KDIGO 2017 CKD–MBD Update
- Endocrine Society Hyperparathyroidism Guidelines
- Mayo Clinic Laboratories - PTH
- ARUP Consult - Calcium/PTH Disorders
- MedlinePlus / NIH - PTH Blood Test