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 2-3 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 (so-called 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 antibody-dye 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