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hCG, Qualitative (Serum Pregnancy Test)

A blood test that says only whether hCG, the pregnancy hormone, is present above the test's cutoff. It is reported as positive or negative.

AI-verified against cited sources. Awaiting expert reviewLOINC 2110-5

What it is

Human chorionic gonadotropin (hCG) is a hormone made by the placenta after a fertilized egg attaches inside the uterus. A qualitative blood test gives a yes or no answer: hCG was found, or it wasn't. It does not tell you how much. Blood tests can find very small amounts of hCG, so they can show a pregnancy before a missed period and earlier than most urine tests.

Why it matters

A positive result usually means pregnancy, so the next step is to contact a clinician to plan care. Blood pregnancy tests are not used as often as urine tests, because urine tests cost less, are very accurate and give results faster (MedlinePlus). A negative result very early can be wrong, so timing matters. If you need to know how much hCG is present, a quantitative hCG test measures the amount.

If it’s low

A negative result means hCG wasn't found above the test's cutoff. If you aren't pregnant, that is the expected result. If you could still be pregnant, a very early test can be negative because hCG hasn't had time to rise. Repeating the test a few days later gives a clearer answer.

Common causes

  • Not being pregnant
  • Testing too soon after conception or implantation
  • Ovulation or implantation later than you thought
  • Biotin supplements affecting some tests (uncommon)
  • An extremely high hCG that reads falsely low (the hook effect, rare)

What can help

  • If your period is late and the test is negative, repeat it in several days or ask about a quantitative hCG
  • Tell the lab or your clinician about any biotin supplement you take

If it’s high

A positive result means hCG was found above the test's cutoff. That usually means you are pregnant. Rarely, hCG comes from something other than a pregnancy. A clinician can confirm the result with a repeat test, a quantitative hCG or an ultrasound.

Common causes

  • Pregnancy
  • A very early pregnancy loss, where hCG briefly rises and falls
  • Fertility medicines
  • Pituitary hCG in some women near or after menopause
  • Test interference from heterophile antibodies (a phantom hCG)
  • Gestational trophoblastic disease or some tumors (rare)

What can help

  • Contact your clinician soon to confirm the result and plan care
  • Ask whether a quantitative hCG test or an ultrasound should come next
  • Tell your clinician about any fertility medicines you use

What can affect your result

  • Timing: hCG can't be found until after implantation, and it rises quickly after that
  • The test's cutoff, which differs between tests and labs
  • Biotin supplements, fertility medicines and the other causes of false results listed above
  • Menopause, when some women have a low level of pituitary hCG
  • Very high hCG, which can read falsely low on some tests
  • Testing too early: hCG can't be detected until a fertilized egg has implanted. On the day of a missed period, serum hCG ranged from under 1 to 3,780 mIU/mL in one report, so a negative result that early can be wrong (Cole 2009). Repeat the test if pregnancy is still possible.
  • Hook effect: an extremely high hCG, as in a molar pregnancy, can read falsely low or negative on some tests. The lab can repeat the test on a diluted sample (Cole 2009).
  • High-dose biotin supplements can falsely lower results on sandwich immunoassays that use biotin chemistry, which could produce a false negative (Ghazal 2022).
  • Heterophile antibodies can cause a false positive, sometimes called a "phantom hCG". A negative urine test with a positive blood test supports this (Oyatogun 2021).
  • Fertility medicines can affect pregnancy test results (MedlinePlus).
  • Pituitary hCG, made by the pituitary gland of some women near or after menopause, can give a positive result when not pregnant (Oyatogun 2021).

Any time of day. hCG rises quickly in early pregnancy, almost doubling every 3 days (MedlinePlus). A blood test can turn positive before a missed period, earlier than a urine test.

When to talk to a clinician

If the result is positive and you have vaginal bleeding, pain in your lower back or belly, or cramping on one side of the pelvis, contact a clinician promptly. These can be symptoms of an ectopic pregnancy (a pregnancy that starts outside the uterus), which can be a medical emergency (MedlinePlus, ACOG). If you feel faint, call 911 or your local emergency number. If the result is positive and you are not pregnant, are past menopause, or are male, ask your clinician about follow-up.

Questions you could ask

  • Could any medicine or supplement I take affect this result?
  • Should I have a quantitative hCG test or an ultrasound next?
  • When should I schedule my first prenatal visit?
  • Should I repeat the test, and how many days should I wait?
  • Would a quantitative hCG test help?

Questions people ask

How early can a blood test detect pregnancy?

Blood tests can find very small amounts of hCG and can show a pregnancy before a missed period (MedlinePlus). No test can detect hCG before the fertilized egg implants, so a negative result very early can still be wrong. Repeat the test in several days if pregnancy is possible.

What is the difference between a qualitative and a quantitative hCG test?

A qualitative test only says whether hCG is present, positive or negative. A quantitative test measures how much is there, which helps follow an early pregnancy over time.

Can a blood pregnancy test be wrong?

Yes, though it is uncommon. A test that is too early can be falsely negative. Fertility medicines, certain antibodies and, after menopause, a small amount of hCG from the pituitary gland can cause a false positive. Your clinician can confirm with a repeat test or an ultrasound.

Show the science and sources

For clinicians and researchers

Qualitative serum hCG is usually a sandwich immunoassay that reports positive or negative at a fixed cutoff. Laboratory quantitative assays have published sensitivities of 1, 2 or 5 mIU/mL, while point-of-care serum and urine tests have published sensitivities of about 20 to 50 mIU/mL (Cole 2009). Commercial pregnancy assays typically detect total hCG (intact, hyperglycosylated and free beta subunit) (Oyatogun 2021). hCG cannot be detected until implantation, and on the day of a missed period the median serum hCG is about 239 mIU/mL with a range of under 1 to 3,780 (Cole 2009). Positive results with no pregnancy should prompt a urine hCG test. A negative urine result with a positive serum result supports heterophile antibody interference, because these large antibodies generally do not pass into urine (Oyatogun 2021). A pituitary source is suggested in a woman near or after menopause when FSH is also high, typically above 30 mIU/mL (Oyatogun 2021). A hook effect above about 500,000 mIU/mL can cause a falsely negative or low result (Cole 2009). A quantitative hCG measures the amount.

LOINC 2110-5 (primary), 2118-8, 80385-8. Specimen: serum.

Sources

  1. Pregnancy Test, MedlinePlus (National Library of Medicine)
  2. New discoveries on the biology and detection of human chorionic gonadotropin, Reproductive Biology and Endocrinology (Cole) (2009)
  3. A rational diagnostic approach to the "phantom hCG" and other clinical scenarios in which a patient is thought to be pregnant but is not, Therapeutic Advances in Reproductive Health (Oyatogun et al.) (2021)
  4. Hormone Immunoassay Interference: A 2021 Update, Annals of Laboratory Medicine (Ghazal, Brabant, Prie, Piketty) (2022)
  5. ACOG Practice Bulletin No. 193: Tubal Ectopic Pregnancy, American College of Obstetricians and Gynecologists (Obstetrics & Gynecology) (2018)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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