Beta-hCG (Pregnancy Test)
Definition
hCG is a hormone produced by the placenta after a fertilized egg implants in the uterus. The test looks for this hormone in a urine or blood sample.
Types of test:
| Type | What it does |
|---|---|
| Qualitative blood test | Gives only a pregnant/not pregnant answer |
| Quantitative blood test | Measures the exact amount of hCG; used to estimate the week of pregnancy and to monitor complications |
| Urine test | 97–99% accurate 1–2 weeks after a missed period. At home or in a clinic |
| Blood test | Can detect pregnancy before a missed period; used less often because of cost and turnaround time |
Purpose
Confirming a suspected pregnancy; confirming the absence of pregnancy before treatments that could harm a fetus; monitoring for miscarriage in high-risk pregnancies; detecting an ectopic pregnancy or molar pregnancy; screening for fetal anomalies as part of prenatal screening.
Results
- Negative, hCG not detected
- Positive, hCG present, typically indicating pregnancy
Normal Values
For the quantitative test, specific to the week of pregnancy; varies by laboratory.
Risks and Limitations
- False negative: testing too early, before enough hCG has accumulated
- False positive: especially with the use of fertility medications
- Timing: hCG is more concentrated in first-morning urine; a diluted sample may give a wrong result
- In home test kits, the appearance of the control line confirms that the test worked properly