Microbiology

Notes

  • The routine pregnancy test has a sensitivity of 25 IU/L.
  • The test will become positive 7 - 10 days after conception and by the time of the first missed period levels frequently exceed 100 IU/L.
  • Dilute urine samples (i.e. with a low specific gravity) may not contain a representative levels of hCG, potentially leading to a false negative result. If pregnancy is suspected, collect an early morning (first) urine sample and retest.
  • A very early pregnancy with low levels of hCG can give a negative result. If pregnancy is suspected a first morning urine sample taken at least 48 hours from the date of this specimen may be of value.
  • hCG levels may remain detectable for several weeks after normal delivery, delivery by caesarian section, spontaneous abortion or therapeutic abortion.
  • Elevated levels of hCG can be caused by a number of conditions other than pregnancy, including trophoblastic disease and some non-trophoblastic neoplasms such as testicular tumours, seminoma, choriocarcinoma, germ cell tumours, hydatiform mole formation, teratoma with elements of choriocarcinoma and islet cell tumour. Therefore, the presence of hCG in urine should not be used to diagnose pregnancy unles these conditions have been ruled out.
  • Serious urinary tract infections (with high levels of WBC, RBC and nitrite) can occasionally cause a false positive pregnancy test result.
  • Ectopic pregnancies typically produce lower levels of hCG than normal preganancies. This will be accentuated by the dilution effect in urine. Therefore, a negative result cannot reliably exclude ectopic pregnancy.
  • Fertility treatments based on hCG may cause false positive results.

Sample requirements

30ml universal container

Urine.

The first urine specimen of the morning is ideal (more dilute urine samples may not contain representative levels of hCG).

30mL sterile Universal

Bottles with boric acid have not been validated for this test and will therefore not be accepted.

Required information

  • Date of LMP.
  • History of ectopic pregnancy or loss of established pregnancy.

Storage/transport

Transport to the lab as soon as possible at ambient temperature.

If transport is delayed, store at 2 - 8°C for up to 48 hours.

Turnaround time

1 - 2 days

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