Beta Human Chorionic Gonadotropin (Beta hCG)

Last updated 25.08.13

 

Index

 

 

Definition

-  Glycoprotein hormone produced in pregnancy by early embryo & placenta

 

Features

-  Acts to maintain corpus luteum to produce progesterone

-  Alpha & beta subunits

-  Similar structure w LH, FSH & TSH

-  Alters TSH, FT4 & T3 in pregnancy

-  First 6-8 weeks of pregnancy levels double every 2 days at levels <20,000

-  Up to 15% normal pregnancies do not

-  6% of ectopics will

-  Levels peak late in 1st trimester

-  At levels >1500 gestational sac should be visible on US

-  Sensitivities

-  Serum 5 IU/L

-  Urine 25 IU/L

 

Indications

-  Pregnancy

-  Diagnosis: ectopic, molar, intra-uterine

-  Maternal Serum Screening (MSS) for Down Syndrome

-  Tumour Marker: germ cell tumour (testicular), islet cell tumour

-  Gestational trophoblastic disease (choriocarcinoma, hydatiform mole)

 

Tests

-  Monoclonal antibody against Beta subunit of hCG

-  Performed on serum or urine

-  Detected after implantation (6-12 days post fertilisation)

 

Procedure

-  Venepuncture

-  OR Dipstick

 

Serum Beta hCG

-  Threshold 5 mIU/ml

-  Quantative

-  99% sensitivity

 

Urine Beta hCG

-  Threshold 25-200 mIU/ml

-  Qualitative

-  75% sensitivity (97.4% technically)

-  Most accureate when 1st urination of day

-  Dilute urine (SG < 1.015) may have false negatives

-  False positives: proteinuria, haematuria, medications (anti-convulsants, diuretics)

 

Pregnancy Test Kit

 

Results

-  Not used to date gestation

-  Reference Levels (since last LMP)

-  3 weeks: 5 – 50

-  4 weeks: 5 - 426

-  5 weeks: 18 – 7,340

-  6 weeks: 1,080 – 56,500

-  7-8 weeks: 7,650 – 229,000

-  9-12 weeks: 25,700 – 288,000

-  13-16 weeks: 13,300 – 254,000

-  17-24 weeks: 4,060 – 165,400

-  25-40 weeks: 3,650 – 117,000

-  Non-pregnant (men or women): <5.0

-  Postmenopausal: <9.5

 

Interpretation

-  >25 = pregnancy

-  <5 not pregnant

-  Low: miscarriage, ectopic pregnancy

-  High: molar pregnancy, multiple pregnancy (twins..)

-  >1,500 mIU/ml gestation sac should be visible on TV US

-  >10,000 mIU/ml foetal heart should be detectable on TV US

-  Normal pregnancy levels double every 48hrs (does not exclude ectopic or miscarriage)

-  Typically in first 6-8 weeks

-  15% normal pregnancies will not double in 48hrs

-  6% of ectopic pregnancies will double in 48hrs

-  Sustained fall in level suggest miscarriage

-  Plateau or slow rise or fall suggests miscarriage or ectopic

-  Fluctuating levels highly suggestive of ectopic

-  For Down Syndrome

-  See Maternal Serum Screening (MSS)

 

 

 

References

 

RWH CPG: Pain & Bleeding in Early Pregnancy, 7/10/2010