Plasma bicarbonate ↑ 10–15% Compensation for chronic hyperventilation

Urine glucose Mild glycosuria with normal blood sugar levels Lowered renal threshold

Renal function GFR increases, Concentrating capacity ↑ Mobilization of retained fluid

Endocrine

Thyroid Total and

Free T4 ↑ and normal respectively

Total and free T3 ↑ and normal respectively

ACTH Markedly ↑ in early months ?

Serum total cortisol ↑ Estrogen—associated rise in binding protein

Serum testosterone ↑ ? ↑ ovarian synthesis

Parathormone ↑ ?

Aldosterone Progressive ↑ Altered plasma volume, renal sodium load

Renin—angiotensin ↑ in latter half With ↑ Na or ↑ blood pressure, level decreases

Contd...

Test Procedure and Interpretation of Results

1. Bring the sealed pouch to room temperature, open the

pouch and remove the device. Once opened, the device

must be used immediately.

2. Dispense two drops of urine/serum specimen into

the sample well ’S’ using the dropper provided.

Refrigerated specimens must be brought to room

temperature prior to testing.

 Read the results at the end of 5 minutes for urine

samples and at the end of 15 minutes for serum

samples as follows:

 Negative: Only one colored-band

appears on the control region ‘C’.

 Positive: In addition to the control band, a distinct colored-band

also appears on the test region.

3. The test should be considered invalid if no band

appears. Repeat the test with a new device.

4. Although, depending on the concentration of hCG

in the specimen, positive results may start appearing

as early as 30 to 60 seconds, negative results must be

confirmed only at the end of the stipulated time.

Pregnancy Tests 421

TROUBLESHOOTING

Latex Methods

Indirect/Latex Agglutination Inhibition Method

Foretel

Problem: False Positive Results

Possible causes Solutions

1. Latex reagent not working The reagents should be stored at 2–8°C. Do not freeze the reagents

Check the working of the latex reagent by mixing with the anti-β hCG reagent

No agglutination indicates deterioration of the latex reagent

2. Anti-β hCG reagent vial is contaminated with known

positive sample. This may be due to the dropper tip

having touched the specimen

Check the anti-β hCG reagent with the latex reagent. If no agglutination is

observed, it indicates that the anti-β hCG reagent is not working

Vial droppers must not be interchanged and reagents of the same lot numbers

should be used

3. Presence of detergent on the slide or in the sample Wash the slide thoroughly with distilled water, wipe dry and retest

Collect urine specimen in a detergent free container

4. Very high hCG levels are found in pathological

conditions like choriocarcinoma and hydatidiform

mole

Do a semiquantitative test and check for high abnormal hCG levels

Check for patient’s history

Problem: Delayed Agglutination

Possible causes Solutions

1. Borderline case with hCG levels just about

0.3 IU/mL

Use the first morning sample. Retest fresh sample after a week

2. Improper mixing of urine and anti-β hCG reagent Mix urine and anti-β hCG reagent as per instructions given in the test protocol

3. Reagents not brought to room temperature before

testing

All reagents must be brought to room temperature before testing. This is

necessary for the antigen-antibody to react optimally

4. Delayed testing Sample should be tested within 12 hours of collection

5. Contaminated urine specimen is used for testing Contaminated urine specimens should not be used for testing

6. Too early diagnosis of hCG levels below detection

limit

Retest after a week using 1st morning sample

Problem: False Negative Results

Possible causes Solutions

1. Case of ectopic pregnancy Follow-up with the patient’s history

2. Threatened abortion progressing into inevitable

abortion

Repeat test and correlate results with clinical findings

3. The urine sample is contaminated, cloudy and

bloody or is used after a long period of time

Specimen should be collected in clean glass of plastic containers free of

detergents or any such material

Specimen should be tested preferably within 12 hours of collection

They can be stored at 2–8°C for up to 72 hours after adding preservatives

thimerosal (0.001%) or sodium azide (0.01%). If the specimen is cloudy

or bloody, centrifuge it at 1000 rpm for one minute and use only the clear

supernatant for testing

422 Concise Book of Medical Laboratory Technology: Methods and Interpretations Latex Agglutination/Direct Method

Foresight®

Problem: False Positive Results

Possible causes Solutions

1. Urine sample may have heavy bacterial growth Check the container used for specimen collection. Specimen should be

collected in a clean and dry container

Do not use grossly contaminated specimens. If the specimen is hazy or bloody,

centrifuge at 1000 rpm for one minute and use clear supernatant for testing

2. Wrong sample tested Label and test correct sample. Record results accordingly

3. Latex reagent contaminated with positive control/

positive sample

Ensure that the dropper tip does not touch the sample/control on the slide

while dispensing

Take one or two drops of the latex reagent on a slide, and check for

granulation, aggregation or agglutination. There should be no granulation,

aggregation or agglutination

4. Presence of detergent on slide Wash slide thoroughly with water,