The pregnancy test
 
All pregnancy test are designed to detect human chorionic gonadotrophin ( H .C . G )
There are many methods to dignosis  of pregnancy .
Immumological methods
1_Sensitive direct latex agglutination test for detection of pregnancy .
2_ Latex particles agglutination inhibition test .
3_ H emagglutination inhibition test .now univer
4_ Radioimmuno assays for the B _ subunit of  HCG .
Sensitive direct latex agglutination test for detection of pregnancy :
The immunological detection of human cgrionic gonadotrorhin ( HCG) is now universally accepted as the presumptive diagnostic test for pregnancy . the (HCG) is secreted by the developing placenta and its appearance in urine can be detedcted as early as 7 days after conception
Principle of test :
The BETATEX  DIRECT PLUS
Kit is a direct latex agglutination test . polystyrene latex particales have been optimally coated  with purified anti_HCG  anti bodies  . In the presence of urine conting HCG an aggkutination reaction  occure  .Agglutination is considered a positive result .
Contens :
Latex : suspension of polystyrene particales (1%) coated with purified anti HCG.
Control + : positive control . phosphate buffer solution contaning HCG .
Control - : negative control . phosphate buffer solution free of GCG .
 
Specimen collection :
Urine samples collected at any time may be used , however it is recommended that to maximise HCG conc. The first voided morning specimen should be collected in aclean dry container (plastic or glass) which must be free from detergent . urine specime should be as fresh as possible and it is preferable to test within 24 hour of collection .the sample may be stored for longer period (72 houer) prior to use , if stored , store at 2_8 c .
Procedure :
1_ Allow kit reagent and patients sample to come room temperature .
2_ plase one drop of urine sample (50 microleter) on to the reaction area of the slide using aclean disposable pipette / stirrere .
3_ Shake the latex reagent , then one drop of latex reagent and mix using the plastic stirrer  . used in step 1
4_ Gently and evenly rock and rotate the test slide for 2 minutes whilst  emamining the test slide for agglutination ,read the test at 2 min.
Rsults and interpretation :
Examine the test slide under astrong light source after 2 min. Apositive result is indicated by the obvious agglutination pattern of the latex . in aclear solution . Anegative result is indicated by no chang in the latex suspension  on the test slide .
Latex particales particles  agglutination inhibition test :
1_obtain arandom urine specimen in clean container free from saop or detergents.
2_plase one drop of anti HCG serum.
3_Add one drop of the urine using aclean dropper.
4_mix thoroughly using wooden stick.
5_Add 2 dropof antigen.
6_Mix the mixture over the entire squre with a wooden stick .
7_Rack slide very slowely and gently for no longer than 90 seconds observe for agglutination .
8_Negetive test agglutination within 90 sec. positive  test no agglutination within90 sec.
Comments
With all bio assays , drugs excreted in the urine may cause daceeased sensitivity and false negative tests , antihistamine , sulfonamides , salicylates , antibiotics and morphine derivatives may cause interference . so the patient should discontinue all medication 3 to 4 days prior the test .
High conc. Of urinary electrolytes ( especially  K+ ) , bacteria and unspecific endogenous subatances , all these may cause false negative reactions .
False positive reactions may be caused by high titers of LH / or FSH due to menopause or primary ovarian failure , as well as drugs especially phenothiazine and promazine.