Fallacies in Urine for Pregancy tests

Pregnancy Tests

Most of the pregnancy tests available to test for the presence of a pregnancy look for the presence of the beta subunit of hcg or human chorionic gonadotropinin in the blood or urine. Human chorionic gonadotropin is a glycoprotein hormone secreted by the  developing placenta shortly after implantation hcg can be detected in the urine and serum of pregnant woman as early as 6-15 days after conception. This hormone is released by trophoblastic tissue in the placenta. However in rare cases it may cell tumours or even other forms of cancer e. g. lung cancer,

Urine tests (Home pregnancy Tests)

Home pregnancy tests are available as kits and though detect pregnancy fairly accurately they should always be followed with blood tests by the physician . Home pregnancy tests work by detecting raised levels of the hormone hcg in the urine. To use a homes pregnancy urine test ones must collect urine in a container and clip the test strip into it . Some tests are available in a solution form and the urine drops have to be added to it. After a waiting time interval (depending on the kind of test used). The results can be read according to the instructions given .

Blood tests                                

A suspected pregnancy can be confirmed with the help of a blood test which also measures the amount of hcg in the blood and confirms the pregnancy . A blood test is more reliable than a urine test. So both are routinely done to confirm conception,

Rapid hcg test card

Rapid hcg test card is used to obtain a visual qualitative result and is intended by professional and laboratory use only. The hcg test card is a rapid test to detect the presence of hcg in urines specimens in a qualitative format sensitive to 10m/u hcg/ml. The test utilizes a combination of monoclonal and polyclonal antibodies reagents to selectively detect elevated level of hcg in urine . The immunological specificity of the test card virtually eliminates cross reactivity interferences from the structurally related glycoprotein hormones FSH,LH, TSH at physiological levels.

Urine or blood pregnancy tests: Which one is better?

Amongst the two types of pregnancy test one tests the blood for the pregnancy hormone hcg while the other checks the urine for this hormone. HPTs using urine testing are inexpensive private and easy to use and are able to tell if one is pregnant about 2 weeks after ovulation. The blood tests to check for pregnancy however are generally used by doctors. Blood tests can pick up hcg earlier in a pregnancy than urine tests can and can confirm the pregnancy about 6-8 days after ovulation. A quantitative blood test measures the exact amount of hcg in the blood and can trace even tiny amounts of hcg thus making it   very accurate. Qualitative hcg blood tests just tests for positive and negative.

Pregnancy Tests sensitivity and hcg values

The pregnancy tests available differ widely in their sensitivity in picking up the pregnancy hormone hcg. As a general rule hcg levels if one is pregnant are between 5-50 mlu a week before the period is due and the hcg levels should double every two to three days. However f is important to remember that every woman is different and the time it takes for the fertilized egg to implant in the uterus wall can vary. A common misconception is that implantation occurs 7 days after conception but the research findings showed that first appearance of HCG occurred 6-12 days after ovulation with 84% of the pregnancies implanting on days 8-10 after ovulation. Hence if one does not get a positive pregnancy test it doesn’t necessarily mean that subject is not pregnant because it is possible that the subject ovulated later than expected or implantation took longer than the average. The amount of hcg or pregnancy hormone in the urine increases with time hence the earlier one takes the test after a missed period the harder it is to spot the hcg. Hence it is best to wait one week after a missed period as one is more apt to have an accurate result at this time.

Various brands of HPT kits are available and are different in sensitiveness. Many HPTs  claim to be 99% accurate on the day one misses the period. But research suggests that most HPTs do not consistently spot pregnancy that  early and even when they do the results are often very faint. In a study done in 2004 researchers tested the accuracy of different brands of HPTs and found that only one brand consistently detected the low levels of hcg usually present on the first day of the missed period. The other tests missed up to 85% of pregnancies on the first day of the missed period however most tests accurately confirmed pregnancies one week after the missed period.

Pregnancy hcg measurement tests:

Advantages of Quantitative tests

Qualitative blood tests generally have a threshold of 25 mlu/ml  and are less sensitive. However quantitative blood tests can detect hcg levels as low as 1 mlu/ml. While urine tests have published detection thresholds between 20 and 100 mlu/ml . Quantitative beta hcg readings are also used in evaluation of trophoblastic and other germ cell tumors.

Quantitative serum beta hcg levels are measured in mlu/ml and a level above 25mlu/ml usually indicates the presence of a pregnancy. Two tests are usually necessary to verify s normal increase. Usually 2-3 days apart. The increase in serum hcg can be interactively monitored. Below an hcg level of 1.200 mlu/ml the hcg usually doubles every 48-72 hours though a rise of 50-60 % is still considered normal. Between 1.200 and 6000 mlu/ml serum the hcg usually takes 72-96 hours to double and above 6000 mlu/ml the hcg often takes more than  four days to double.

Failure to increase normally may indicate that the pregnancy is not developing well and can be an early sign for a possible miscarriage or an ectopic pregnancy. After a miscarriage.HCG levels fall steadily back to the non pregnancy range. Also an ectopic pregnancy may be suspected when hcg levels fail to double particularly if the hcg level rises fails and rises again.

Role of ultrasound in pregnancy detection

Once a pregnancy has advanced past first 6-8 weeks, the pregnancy is usually easier to follow by ultrasound as more information is obtained in real time. In general a pregnancy is detectable 25 days after ovulation by transvaginal sonography (usually corresponding to an hCG level of >1.500 miu/ml).       

Home Pregnancy Tests: Drug Interactions

Most medicines, over the counter and prescription, including birth control pills and antibiotics, does not affect the results of a home pregnancy test. Alcohol and illegal drugs do not affect HPT results. Only medicines that have the pregnancy  hormone hCG, such as ones used to treat infertility can give a false positive test results.

A  Faint Line on a pregnancy Test May Mean:

On a pregnancy test, a faint test line, or color band  is usually indicative of a positive result, as long as it’s read  within the allotted reaction time of the test (usually at 3-5 minutes). Explanations for faint positive line include:

.One may be testing too early after conception – the hCG in the body may not be a sufficient level for test detection. Since, hCG doubles every  two days, one should wait and test again using first morning urine.

.Different test sensitivity: As tests detect hcg at different levels a faint line on one variety of test may appear as a stronger line on a different 20mlu test.

Urine dilution may be present: Urine may be diluted due to frequent urination or consumption of liquid hence first morning urine is recommended for pregnancy testing as it contains the most concentrated presence of hcg.

Chemical pregnancy: At times an early pregnancy is detected followed by negative test results. A chemical pregnancy means implantation takes place followed by a miscarriage- usually before any other pregnancy symptoms are detected.

False positive and False negative tests

False negative readings can occur when testing is done too early and earlier the test is performed the higher the chance of a false negative result. A false negative result can also stem from using a diluted urine samples  apart from taking a test too early in pregnancy. First morning urine contains the most concentrated presences of hcg which makes it the ideal sample for pregnancy testing.

False positives tests are rare though there are instances and conditions where they can occur in case some tissues in a  non pregnant woman produce hgc, it may gives a false positive test . False positive results can result from diseased likes choriocarcinoma igA deficiencies heterophile antibodies enterocystoplasties ,gestational trophoblastic diseases gestational trophoblastic neoplasms and testicular germ cell malignancies . Secondly research indicates that half of all conceptions do not go forward to develop as pregnancy and may abort . A false positive can be seen in this situation. M

Medications that can cause a false positive are the fertility medications that  contain hcg. However fertility drugs and medications that do not contain hcg will not precipitate false positive as well. A percentage of false positives pregnancy test can also be attributed to misinterpretation of results due to a failure to follow test instructions with precision. Additionally at the same gestational stages, women produce quantitatively different levels of hcg. Hence the first indication of positive result on a home pregnancy test may vary between women despite similar gestational stage.

 HCG from urine :: Evaporation lines : 

Moreover many homes pregnancy tests show a positives or unclear result when read well after the suggested 3-5 minute window, independent of an actual pregnancy. This type of false positive is known as and evaporation line.

Phantom hcg:

Some individuals react to some substrate in the test and thus will display a consistently low positive blood pregnancy test even though they are no pregnant. This phantom hcg may lead to serious misdiagnosis and intervention but can be detected with serial dilutions. Patients with phantom hcg have a postitivse blood hcg but a negative urine hcg test .

Need for patience in pregnancy tests

Since, pregnancy tests look for the hcg hormones which is produced once the fertilized egg has implanted in the uterine wall in most cases this happens about 6 days after conception. A positives pregnancy test, further confirmed to be healthy by ultrasound techniques, makes all the hard work and effort of planning pregnancy worthwhile. But studies show that in up to 10 percent of women ,the embryo doesn’t implant until much later after the first day of the missed period. Hence homes pregnancy tests will be accurate as soon as one day after a missed period for some women but not for others, And because the amount of hcg in the urine at different points in early pregnancy is different for every woman some women will have accurate results on the day of the missed period while others will need to wait longer. But whatever may be time period a positive pregnancy test further confirmed to be healthy by ultrasound techniques, makes all the hard work and effort of planning pregnancy worthwhile.