courtesy to all sources .

1. Parathyroid Hormone
Dr.Ghulam Murtaza
Chemical Pathology PGY 1
DIMC

2. Biochemistry & Physiology
• The primary regulator of PTH are free calcium ,1,25 (OH)2D, &
Phosphate
• PTH acts directly on bone & kidneys & indirectly on intestine via 1,25
(OH)2D to increase plasma concentration of free calcium & decrease
plasma concentration of phosphate
• Its metabolism is degraded by liver & cleared by kidney .

3. Synthesis & secretion :

4. Synthesis & secretion
• The biologic activity of PTH resides in the N-terminal of the molecule.
• Synthetic PTH (1-34) is least potent than intact ( 1-84 ) in interacting
with the PTH/PTHrP receptors .
• C-terminal metabolite of PTH (7-84) has some effect that antagonize
intact PTH function because having own receptors in kidney & bone

5. • PTH secretion exhibits seasonal and circadian fluctuations
synchronous with changes in serum calcium, phosphate, and bone
turnover
• an ultradian rhythm exists that comprises of seven pulses per hour,
accounts for 30% of basal PTH release, and is highly sensitive to
changes in ionized calcium.
• Acute hypocalcemia induces a selective, several-fold increase in pulse
frequency and amplitude, whereas hypercalcemia suppresses the
pulsatile release

6. Biological Action :

7. Heterogenicity of Circulating Parathyroid
Hormones .
• PTH circulates partially as biological active & partially as a series of N-
terminal truncated fragments containing mid region & C-terminal
amino acids
• Heterogenicity is due to secretion of both intact hormone & C-terminal
fragments by parathyroid glands
• Biological active intact (1-84) is rapidly cleared from plasma ( half life
< 5 minutes ) in normal subjects by liver (60-70%) & by kidney (20-
30%).

8. In subjects with
normal renal
function 5-25% is of
the total circulating
PTH is INTACT
Hormone &
75-95% consists of
C-terminal
fragments

9. Hyperparathyroidism :
Primary Secondary Tertiary
Definition Unregulated overproduction of
PTH resulting in abnormal
calcium homeostasis
Overproduction of PTH secondary to
a chronic abnormal stimulus for its
production (physiologic)
Excessive secretion of PTH
after longstanding
secondary
hyperparathyroidism (low
vitamin D or CKD)
Cause Adenoma
Familial (MEN 1/ MEN2)
CKD 5
Vit D deficiency
Malabsorption
Prolonged secondary
hyperparathyroidism
Long standing CKD
LABS Raised Ca
Raised PTH
Low P
Mild-to-mod increase in 24-hour
urinary Ca excretion
Low-normal Ca
Raised PTH
P levels depend on etiology (e.g.,
high in CKD, low in VDD)
Raised Ca
Raised PTH
P often raised
Vitamin D normal

10. Hypoparathyroidism Pseudohypoparathyroidism
• Thyroid Surgery is most common
cause ( planned or accidently )
• Serum Ca decreased
• Serum Phosphate is increased
• serum PTH subnormal or low
• Peripheral resistance to PTH
rather than a deficiency
• Serum Ca decreased
• Serum Phosphate is increased
• serum PTH High

11. Intraoperative PTH measurement :
• Because of short half life (<5 minutes ) intraoperative determination
of intact PTH can be used to assess the completeness of
parathyroidectomy & to facilitate MIPS to improve cost effectiveness
& cosmetic outcomes
• PTH is measured just before incision & 20 minutes after resection of
hyperfunction of parathyroid tissue
• A decline in 50 % of PTH is usually considered as a successful removal
of hyper functioning tissues

13. • PTH concentration may be altered in Hyperthyroid ,in hypothyroid &
with Lithium carbonate treatment
• PTH is inversely related with T3 concentration in hyperthyroid &
increase in hypothyroid .
• Long term lithium therapy has been reported to increase parathyroid
gland size & intact PTH

14. Measurement of Parathyroid Hormones
• In the first gen, noncompetitive, “sandwich” type assay, a single
polyclonal antibody competes for labeled PTH and the serum forms
• In the 2nd-gen assays, immunometric, 2 distinct antibodies (usually
monoclonal), directed against different epitopes, bind the PTH forms
present in the sample. One of the antibodies is bound to a solid
phase, and the other is labeled
• In the third gen assays, the recognition is based on other principles
(mass spectrometry) in serum samples previously purified

16. Immunometric assays a break through
• Recognition of PTH by two different antibodies, one carboxyl terminal and
the other amino terminal
• Widely available
• Adapted to most of the automation platforms
• Specificity of the amino terminal antibody defines if the assay measures
only the bioactive PTH circulating form (including the first amino terminal
amino acids) or the “intact” PTH, which includes, besides bioactive PTH,
other “long” carboxyl-terminal forms, for example, 7–84-PTH
• Assays for “intact” PTH are the most commonly available and the potential
advantage of the bioactive PTH assays is still debatable

17. PTH Half Life
• The native or intact (1-84) PTH has a short half-life, 2-4 minutes
• Whereas the carboxy and midmolecule fragments, which are
biologically inactive, have half- lives less than one hour .
• The high concentrations of biologically inactive fragments have
interfered with use of C-terminal or mid molecule assays for
evaluation of parathyroid function in patients with impaired renal
function.

18. Specimen requirement :
• Specimen required may depends on the specific assay method
• EDTA plasma is often preferred ( due to more
stability due to reduced proteolytic activity )
• Lower concertation is observed in serum when
stored at room temperature for few hours

19. Reference intervals
• Depend on method used & vitamin D status of population sampled .
• Intact PTH -10-65pg/ml or 1.1to 6.8 pmol/L
• Intact PTH vary with age (healthy individuals ),are low or normal
during pregnancy increased during first few days of life due to
neonatal hypocalcemia

20. In our lab :

21. Parathyroid Hormone- Related Protein
• PTHrP was discovered as agent responsible for causing known state as
humoral hypercalcemia Of malignancy (HHM) in certain cancer
• Later proved to be an autocrine /paracrine factor with multitude of
function in several organ system
• Affect on chondrocyte biology ,calcium metabolism in fetus ,during
fetus & lactation (higher conc)

22. Biochemistry & physiology
• Located on chromosomes 12 ,three isoforms of 139,141 & 173 amino acids
exits ,
• N-terminal end of the molecular shows close homology to PTH with 8 of
the first 13 amino acids being identical & 3 being identical next 21 amino
acids
• PTHrP activity is contained in N-terminal amnio acids (1-34) like PTH
• The common N-terminal explain the ability of PTHrP to interact with
receptors ,mimicking PTH action in (bone & kidney )

23. Measurement of PTHrP
• Several competitive immunoassays ha been developed to measure in
sera from patient suffering from HHM like N-Terminal ( PTHrP 1-34 )
mid region 37-67,37-74 & C-terminal 109-138 .
• N-terminal (1-34) has been used most widely
• Currently available assays used antibodies against PTHrP ( sequences
37-74, 1-40,1-34 as a capture antibodies

24. Specimen required
• PTHrP is unstable in Serum & plasma at room temp ,unless collected in
presence of protease inhibitors
• A combination of aprotinin ,leupeptin ,pep statin & EDTA provides the
greatest protection.
• In general specimen should be collected with protein inhibitors & kept on
ice.
Reference range :
• In healthy individual : undetectable to 5pmol/L

25. Interpretation
• Presence Of PTHrP is poor prognostic indicator .
• PTHrP is increased in 50-90% of patient with HHM , in addition with
squamous cell carcinoma of lungs ,head ,neck ,esophagus ,cervix &
skin .
• Increased concentration also has been found in B-cell lymphoma
,leukemia ,pheochromocytoma ,renal ,breast & ovarian carcinoma .

26. •References
•Tietz text book of clinical chemistry
•Chemical Pathology for the beginners
Thanks

27. Q ;
Q.1: Blood sample of parathyroid hormone (PTH) is
transported in ice because its half-life is:
a. 20 seconds
b. 30 seconds
c. 2-4 min
d. 8-10 min
e. 15 min