forming a well-defined ring. This is a positive reaction. If

the urine does not contain hCG, the still active antiserum

will agglutinate the hCG-sensitized red cells, which will

form an evenly dispersed layer on the bottom of the test

tube. Thus, the test can be regarded as a hemagglutination

inhibition test. This is not affected by proteinuria.

Both procedures may be performed with dilutions

of urine in order to assess the 24 hours output of hCG in

the follow-up for placental-trophoblastic tumors. The

hemagglutination test is easier to read and the slide test

requires less time and less equipment. The use of known

positive and negative controls is strongly recommended

for both methods. Latest methods using ELISA (enzymelinked immunosorbent assay) are being marketed, these

are more sensitive tests.

SLIDE TEST FOR PREGNANCY

(Foretel® from Tulip Group of Companies)

Latex Agglutination Inhibition Method

Summary

Human chorionic gonadotropin (hCG), a hormone

produced by viable placental tissue during pregnancy,

is excreted in urine approximately 20 days after the last

Pregnancy Tests 413

menstrual period. The levels of hCG rise rapidly reaching

peak levels after 60 to 80 days and then the hCG levels fall

suddenly and eventually plateau out.

The hCG molecule consists of two combined dissimilar

subunits namely, alpha and beta. The alpha subunit is

practically identical to the alpha subunit of luteinizing

hormone (LH), follicle-stimulating hormone (FSH),

thyroid stimulating hormone (TSH) and the pituitary

glycoprotein hormone. The beta subunit of hCG, by virtue

of its unique amino acid sequence and content, confers

biological and immunological specificity to the entire hCG

molecule.

The appearance of hCG in urine soon after conception

and its rapid rise in concentration make it an ideal marker

for detection and confirmation of pregnancy. However,

elevated hCG levels are frequently associated with

trophoblastic and non-trophoblastic neoplasms; these

conditions should be considered before a diagnosis of

pregnancy can be made.

FORETEL slide test for pregnancy employs monoclonal

antibodies specific to the beta subunit of hCG.

Reagents

1. Anti-beta human chorionic gonadotropic antibody

(mouse monoclonal); The antibodies are adjusted to

provide a sensitivity of about 0.3 IU/mL of hCG.

2. Suspension of polystyrene latex particles to which

hCG has been chemically coupled. Each batch of

reagents undergoes rigorous quality control at various

stages of manufacture for its specificity, sensitivity and

performance.

Reagent Storage and Stability

a. Store the reagents at 2–8°C. Do not freeze.

b. The shelf life of the reagents is as per the expiry date

mentioned on reagent vial labels.

Principle

FORETEL slide test for pregnancy utilizes the principle of

latex agglutination inhibition. The urine specimen to be

tested is first mixed with the antibody reagent containing

antibodies directed against the beta subunit of hCG. Then

hCG coupled latex reagent is added and the mixture is

allowed to react. When the urine specimen is from a nonpregnant woman and does not contain hCG, the antibeta hCG monoclonal antibodies will be free to react

with latex coupled hCG causing agglutination. When the

urine specimen is from a pregnant woman and contains

atleast 0.3 lU/mL of hCG, the anti-beta hCG monoclonal

antibodies will be neutralized and will not react with latex

coupled hCG antigen. Hence, no agglutination will be

observed.

Note

1. In vitro diagnostic reagent for laboratory and professional use only. Not for medicinal use.

2. The reagents contain sodium azide, 0.1% as

preservative. Avoid contact with skin and mucosa.

On disposal flush with large quantities of water.

3. The reagents can be damaged due to microbial

contamination or on exposure to extreme temperatures. It is recommended that the performance of

reagents should be verified by testing with known

positive and negative urine controls.

4. Use reagents of the same lot numbers. Do not

interchange reagents to different lot numbers.

5. Do not interchange vial droppers.

6. Shake the latex antigen vial well before use to disperse

the latex particles uniformly and improve test

readability.

7. Only a clean and dry glass slide must be used. Clean

the slide with distilled water and wipe dry. Do not use

detergents, soaps or organic solvents to clean the slide.

Sample Collection and Preparation

Qualitative Method

Though random urine specimens can be used, first

morning urine specimen is preferable. Specimens should

be collected in clean glass or plastic containers free of

detergents. Specimens should be tested immediately

preferably within 12 hours of collection. Should a delay

in testing occur,