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Molar pregnancy with false negative urine hCG: the hook effect
1Department of Obstetrics and Gynaecology, Singapore General Hospital, Outram Road, Singapore 169608. cindypangyp@yahoo.com
Singapore Medical Journal
|April 30, 2010
Summary
Urine pregnancy tests can give false negatives in cases of molar pregnancy due to the hook effect. This can lead to misdiagnosis, highlighting the need for further testing when pregnancy is suspected.
Area of Science:
- Gynecology
- Clinical Chemistry
- Emergency Medicine
Background:
- Urine pregnancy tests are standard in emergency departments for reproductive-age patients with gynecological issues.
- These tests detect human chorionic gonadotropin (hCG) to rule out pregnancy.
Observation:
- A case of complete molar pregnancy presented with a false negative urine pregnancy test.
- The false negative result was attributed to the 'hook effect,' where high beta-human chorionic gonadotropin (beta-hCG) levels oversaturate the assay.
- This led to an initial misdiagnosis of a degenerative fibroid.
Findings:
- The hook effect can cause false negative urine pregnancy tests in conditions with high beta-hCG, such as molar pregnancy.
- Misdiagnosis can occur if the possibility of a false negative test is not considered.
Implications:
- Physicians must be aware of potential false negatives in urine pregnancy testing.
- Patients with high suspicion of pregnancy and negative or inconclusive urine tests require further evaluation, including serum beta-hCG quantification and sample dilution.
