360 - Hormones Flashcards
most common hormone tests performed in core
hCG and thyroid
how can hormones be measured?
several techniques, including immunoassay and instrumental techniques such as GC-MS
how can hormones be measured?
several techniques, including immunoassay and instrumental techniques such as GC-MS
sample collection or hormone assay considerations
- nutrition
- diurnal variation
serum iodide is trapped in the ________, and iodine is incorporated into ___________.
thyroid; tyrosine
this is key to the synthesis of the thyroid hormones
iodine
- rate-limiting step is the iodine transport to the follicles
the process of thyroid hormones being released
- TRH from hypothalamus secreted due to low thyroid hormone concentrations
- TRH interacts w anterior pit gland = TSH
- TSH binds to thyroid follicular cells = T3 and T4, and reverse T3
the major secretory product of the thyroid
T4
30X higher in plasma than T3
Both free and bound hormones are found in circulation
T3 and T4 transported in blood by this
TBG; thyroid binding globulin
transthyretin
albumin
This binding protein has the greatest affinity for T4
TBG
also the most important in regulating free T4 concentration
In the ________, free T4 is deiodinated to create biologically active ___.
liver; T3
what does T3 do?
regulates the rate of cellular oxidation and metabolism
T3 helps regulate cellular uptake of glucose and influences protein metabolism
T or F. Increased thyroid hormone concentrations inhibit the pituitary response to TRH
T!
T or F. An increase in thyroid hormone concentrations will cause an increase in TRH and TSH secretion
F! Decrease in thyroid hormone…
Graves’ disease
characterized by the formation of autoantibodies specific to the TSH receptor
The autoantibodies stimulate the receptor leading to hyperthyroidism
Hashimoto thyroiditis
characterized by cell-mediated autoimmunity, causing thyroid dysfunction
clinical presentation includes goitre, thyroiditis, and frequently hypothyroidism
hypothyroidism
general term for thyroid hormone deficiency or lack of response to thyroid hormone
primary hypothyroidism
- endogenous or exogenous
- most common cause of endogenous hypothyroidism is autoimmune thyroid disease (e.g. Hashimoto thyroiditis)
- Exogenous hypothyroidism is associated with iodine excess or deficiency and various medications
secondary hypothyroidism
the result of damage/disease of the hypothalamus or pituitary gland
a condition characterized by excess production of thyroid hormones resulting in hypermetabolism
hyperthyroidism
- endogenous vs exogenous
Endogenous causes of hyperthyroidism
Graves’ disease
thyroid tumours
disorders of the hypothalamus or pituitary gland
Exogenous hyperthyroidism
associated w viral and bacterial thyroiditis
Non-thyroidal illness (NTI)
presents w low total and free T3, elevated reverse T3, and normal to low TSH in the absence of true thyroid disease
NTI is seen in…
starvation,
sepsis,
surgery,
myocardial infarction,
diabetes,
many other severe illnesses
NTI underlying problem
lack of conversion of T4 to T3 at the tissue = appears to be multifactorial and includes …
suppression of TRH release,
reduced T3 and T4 turnover,
reduction in liver generation of T3,
increased the formation of rT3,
tissue-specific down-regulation of receptors, transporters, and enzymes
Progressive testing protocol for thyroid function testing
progressive testing with TSH as the primary screening test
TSH is the most sensitive and specific test for the investigation and management of primary thyroid dysfunction.
TSH (in comparison to total T4 or free T4) is not as markedly affected by physiologic alterations resulting from severe non-thyroidal sickness or by the administration of therapeutic drugs
hCG
a glycoprotein molecule (hormone) produced by the placent
- has two subunits: alpha and a beta chain
β subunit is specific to hCG
α subunit is also found in TSH, LH, and FSH
hCG acts on the ____________ _________.
corpus luteum = produces progesterone until the placenta can produce enough progesterone to maintain the pregnancy
Progesterone prevents menses
qualitative hCG in the urine can be used to diagnose…
pregnancy (as early as eight days after fertilization)
Quantitative levels of serum or plasma hCG can be used to:
date pregnancy
detect multiple pregnancies (2X normal level with twins)
assist in the detection of ectopic pregnancy
Increased intact hCG and free β subunit can be observed in:
trophoblastic disease (choriocarcinoma, hydatiform mole) germ cell tumours (primarily tumours of the testis, ovaries)
other cancers (biliary, pancreatic)
Serial measurement of hCG is used to monitor treatment and progression of…
trophoblastic disease
When using hCG as a tumour marker one should measure both of these
intact hCg and free B subunits
Prenatal screening is used to determine the risk of having a fetus with serious birth defects such as…
neural tube defect or Down’s syndrome
The first trimester screen is performed between…
10 and 13 weeks gestation
first trimester screening
- 10 to 13 wks
- blood is quantitatively tested for hCG and the pregnancy associated plasma protein A (PAPP-A) NOTE: HCG and PAPP-A are produced by the placenta
- Down’s syndrome PAPP-A is relatively low while HCG is relatively high
- these are interpreted in conjunction with a nuchal translucency test; increased nuchal space is associated with Down’s syndrome
nuchal translucency test
In the nuchal translucency test, the subcutaneous space between the skin and cervical spine of the fetus is measured
a prenatal test that measures levels of four substances in a pregnant woman’s blood to estimate the risk of open spina bifida, anencephaly, trisomy 21, and trisomy 18
MoM (Multiples of the Median) or Quad screen
second trimester
substances measured in MoM
- Alpha-fetoprotein (AFP), a protein made by the developing baby
- Human chorionic gonadotropin (hCG), a hormone made by the placenta
- Unconjugated estriol 3, a hormone made by the placenta and the baby’s liver
- Dimeric Inhibin A, another hormone made by the placenta
Multiple of the median is a statistical value that measures…
how different a patient result is from the median result of a similar population
it’s used in situations where individual test results are highly variable (such as in pregnancy) and are typically used for screening purposes
MoM results greater than cutoff value = additional testing
NOTE: cut off value does not have a 100% positive or negative predictive value
