Transcript Human chorionic gonadotropin

Human chorionic
gonadotropin
•
The hormone human chorionic gonadotropin (better known as
hCG) is produced during pregnancy.
•
It is made by cells that form the placenta, which nourishes the
egg after it has been fertilized and becomes attached to the
uterine wall.
•
Levels can first be detected by a blood test about 11 days after
conception and about 12 – 14 days after conception by a urine
test.
•
In general the hCG levels will double every 72 hours. The level
will reach its peak in the first 8 – 11 weeks of pregnancy and
then will decline and level off for the remainder of the
pregnancy.
•
pregnancy test is done using blood or urine. There are two
types of blood tests:
•
Qualitative, which measures whether the HCG hormone is
present
•
Quantitative, which measures how much HCG is present
•
There are two common types of hCG tests. A qualitative hCG
test detects if hCG is present in the blood. A quantitative hCG
test (or beta hCG) measures the amount of hCG actually
present in the blood.
Structure
•
Human chorionic gonadotropin is a glycoprotein composed of
237 amino acids with a molecular mass of 25.7 kDa.
•
It is heterodimeric, with an α (alpha) subunit identical to that
of luteinizing hormone (LH), follicle-stimulating hormone
(FSH), thyroid-stimulating hormone (TSH), and β (beta) subunit
that is unique to hCG.
•
The α (alpha) subunit is 92 amino acids long. The β-subunit of hCG
gonadotropin (beta-hCG) contains 145 amino acids,
•
The two subunits create a small hydrophobic core surrounded by a
high surface area-to-volume ratio: 2.8 times that of a sphere. The
vast majority of the outer amino acids are hydrophilic
•
The hCG hormone is measured in milli-international units per milliliter
(mIU/ml).
•
An hCG level of less than 5mIU/ml is considered negative for pregnancy,
and anything above 25mIU/ml is considered positive for pregnancy.
•
An equivocal test of between 5 and 25 mIU/cc requires a repeat within 23 days. If if goes higher then that's a good sign, but if it goes lower or
stays about the same then that's a sign that the pregnancy has failed
•
Blood hCG testing is much more sensitive than a urine HPT. This means
that the blood test can detect pregnancy several days earlier than the
urine test, as early as 2-3 days after implantation or 8-9 days after
fertilization.
•
Urine tests measure the urine HCG qualitatively, which means that the
HPT results are either "positive" or "negative." Around the time of the
first missed period (14+ days after ovulation), over 95% of HPTs are
usually positive.
•
Implantation happens as early as 6 days after ovulation/fertilization
(usually about 9 days after ovulation), so blood hCG human chorionic
gonadotropin can be found as early as 8-9 days after
ovulation/fertilization.
•
A maximum level is usually reached by the 10th or 11th week.
•
After 10 weeks or so, hCG normally decreases.
•
Urine tests it is possible to end up with false results (positive &
negative ) from blood test.
•
False negative ,if the test performed too early (not enough HCG).
•
False positive ,if female taken medication contains HCG.
hCG levels in weeks from LMP
(gestational age) :
•
3 weeks LMP: 5 – 50 mIU/ml
•
4 weeks LMP: 5 – 426 mIU/ml
•
5 weeks LMP: 18 – 7,340 mIU/ml
•
6 weeks LMP: 1,080 – 56,500 mIU/ml
•
7 – 8 weeks LMP: 7, 650 – 229,000 mIU/ml
•
9 – 12 weeks LMP: 25,700 – 288,000 mIU/ml
•
13 – 16 weeks LMP: 13,300 – 254,000 mIU/ml
•
17 – 24 weeks LMP: 4,060 – 165,400 mIU/ml
•
25 – 40 weeks LMP: 3,640 – 117,000 mIU/ml
•
Non-pregnant females: <5.0 mIU/ml
•
Postmenopausal females: <9.5 mIU/ml
Tumor marker
•
Human chorionic gonadotropin can be used as a tumor
marker as its β subunit is secreted by
some cancers including seminoma, choriocarcinoma, germ
cell tumors, hydatidiform mole formation, teratoma with
elements of choriocarcinoma, and islet cell tumor.
•
For this reason a positive result in males can be a test
for testicular cancer.
•
The normal range for men is between 0-5 mIU/mL.
ectopic pregnancy
•
An ectopic pregnancy, or eccysis, is a complication of
pregnancy in which the embryo implants outside the uterine
cavity.
•
With rare exceptions, ectopic pregnancies are not viable.
Furthermore, they are dangerous for the mother, since internal
haemorrhage is a life-threatening complication.
•
Most ectopic pregnancies occur in the Fallopian tube (socalled tubal pregnancies), but implantation can also occur in
the cervix, ovaries, and abdomen(non tubal pregnancies).
•
An ectopic pregnancy is a potential medical emergency, and, if
not treated properly, can lead to death.
PRINCIPLE OF THE TEST
• The pregnancy testing device contains a unique set of dye-conjugated and
immobilized antibodies used to produce a distinctive visual pattern
indicating elevated concentration of hCG (=25 mIU/ml) in the test
sample.
• One antibody, the capture antibody, is in a solid phase permanently
attached to a tube, plate, membrane, or bead.
• Conjugate pad contains the label reagent, i.e. antibody labeled with
either red, gold or blue latex particles.
• Sample is applied and dissolves the label mixture and migrates to the
zone of immobilized antibody lines. If hCG is present, labeled antibodydye conjugate binds it, forming an antibody-antigen complex.
• Positive, that is hCG containing, sample causes the formation of a colored
test line, which indicates a positive test result.
•
As the reaction mixture continues to flow along the test membrane,
the complex binds to the anti-hCG antibody in the test zone of the
membrane, and produces a color band.
•
Unbound conjugate binds to the reagents immobilized in the control
zone producing a color band, demonstrating proper performance of
the test.
1. Device with solid phase capture antibody to one site on hCG, and
liquid phase tracer antibody (label shown by red star) to second or
distant site on hCG. In this way the label becomes immobilized.
2. Serum or urine containing hCG (shown as ab) added to device. The
hCG forms a sandwich or bridge between capture and tracer
antibody. After a short incubation period the hCG binds both the
solid phase and liquid phase antibodies linking them.
3. Excess tracer antibody is washed away. Amount of label or tracer
(red star) is measured. This is proportional to amount of hCG.
Principle of urine pregnancy strip