Several hormones can be measured and monitored to aid in the diagnosis of pregnancy The most commonly used assays are for the beta subunit of hCG Other hormones that have been used include progesterone early pregnancy factor (EPF).
HCG This hormone is only released by trophoblastic tissue, usually is produced by a growing fetus and its associated placenta. (rarely, from a choriocarcinoma or some other germ cell tumours.) hCG is a glycoprotein similar in structure to follicle-stimulating hormone, luteinizing hormone (LH), and thyrotropin. The free beta subunit of hCG differs from the others in that it has a 30–amino acid tailpiece at the COOH terminus. Free beta subunits are degraded by macrophage enzymes in the kidney to make a beta subunit core fragment which is primarily detected in Urine samples.
Detection of HCG in maternal serum and urine is evident only after implantation and vascular communication has been established with the decidua by the syncytiotrophoblast 8-10 days after conception. Time of detection is related to the sensitivity of the assay being used. Most current pregnancy tests have sensitivity to approximately 25 mIU/mL theoretically, But ranges from 25 to 100mIU/mL. Sample reference list for HCG levels in singleton pregnancies, based on days past ovulation (DPO): * At 14 DPO, the average HCG level is 48 mIU/ml, with a range of 17-119 mIU/ml. * At 15 DPO, the average HCG level is 59 mIU/ml, ( 17-147 mIU/ml.) * At 16 DPO, the average HCG level is 95 mIU/ml, ( 33-223 mIU/ml.) * At 17 DPO, the average HCG level is 132 mIU/ml, (17-429 mIU/ml. ) * At 18 DPO, the average HCG level is 292 mIU/ml. (70-758 mIU/ml.) * At 19 DPO, the average HCG level is 303 mIU/ml, ( 111-514 mIU/ml.) * At 20 DPO, the average HCG level is 522 mIU/ml, ( 135-1690 mIU/ml.) * At 21 DPO, the average HCG level is 1061 mIU/ml, ( 324-4130 mIU/ml.) * At 22 DPO, the average HCG level is 1287 mIU/ml, ( 185-3279 mIU/ml.) * At 23 DPO, the average HCG level is 2034 mIU/ml, ( 506-4660 mIU/ml.) * At 24 DPO, the average HCG level is 2637 mIU/ml, ( 540-10,000 mIU/ml.) Accordingly, the key to interpreting the true value of HCG measurements is to look at their progression. In general, the HCG level will double every two to three days in early pregnancy.
False-positive serum hCG results are usually due to interference by non-hCG
substances or the detection of pituitary hCG.
Some examples of non-hCG substances that can cause false-positive results include
human LH, anti animal immunoglobulin antibodies, rheumatoid factor,
heterophile antibodies and binding proteins.
Most false-positive results are characterized by serum levels that are generally less than 1000 mIU/mL and usually less than 150 mIU/mL.
Some of the substances that can cause serum false-positive results have much higher molecular weights that are not easily filtered through the renal glomeruli; therefore, they do not produce a positive urine test.
False-negative hCG test results usually involve urine and are due to the qualitative nature of the test.
an hCG concentration below the sensitivity threshold of the specific test being used.
a miscalculation in the onset of the missed menses,