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Three Part Question

In [women of child bearing age], are [home pregnancy tests] accurate in determining [pregnancy]?

Clinical Scenario

A 22 year old female presents to the emergency department with a positive home pregnancy test. She had been sexually active and her last menstrual perior only 2 weeks ago. She wants to know if her home test is correct.

Search Strategy

Medline 1950-05/09 using OVID interface, Cochrane Library (2009), PubMed clinical queries.
[(exp pregnancy tests) AND (exp sensitivity and specificity)]. Limit to human and English.

Search Outcome

47 papers were found of which 3 were relevant to the three part question. These studies included a meta-analysis (1998) and 2 clinical studies published after 1998.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Cole LA, et al. 2004 USA	Urine samples from 5 nonpregnant females were obtained and varying amounts of recombinant hCG was added to achieve concentrations of 0 to 100 mIU/mL. Prior to the study, urine hCG concentrations of 25 pregnant women in the first 4 days of missed menses was measured. It was determined that detection of 12.5mIU/mL of hCG would yield a sensitivity of 95%. 18 brands of HPTs were tested to determine their ability to detect pregnancy at these varying hCG concentrations. The tests were read at the suggested time per the manufacturer and also at exended read times.	Prospective, observational study	Sensitivity at hCG level of 12.5 mIU/mL	0% clearly positive, 6% faintly discernible	Study not completely blinded. Extended reading times were also tested and showed improved senstivities. However, it is unlikely that the lay consumer would consider extending the read time without proper education.
			Sensitivity at hCG level of 25 mIU/mL	0% clearly positive, 17% faintly discernible
			Sensitivity at hCG level of 50 mIU/mL	22% clearly positive, 44% faintly discernible
			Sensitivity at hCG level of 100 mIU/mL	44% clearly positive, 83% faintly discernible
Butler SA, et al. 2001 USA	592 urine samples were obtained from pregnant women carrying singleton pregnancies during all 3 trimesters. 15 HPTs were used to test urine samples for all forms of hCG (all-hCG), including H-hCG which is the predominant form of the hormone during the first 2 weeks since last menses. Varying concentrations (6.3, 13, 25, 50 IU/L) of all-hCG and H-hCG were tested.	Prospective, blinded clinical trial	Proportion of H-hCG to all-hCG at various times during pregnancy	60% H-hCG reactivity during 4th week since menses, Less than 5% during 2nd and 3rd trimester.
			Senstivity HPTs to urine H-hCG	11/15 tests detect H-hCG, 6/15 tests detect H-hCG as effective as all-hCG.
Bastian, LA. et al. 1998 USA	Five studies from 1972-1993 were reviewed. Range of senstivities of HPTs were measured when the tests are performed by volunteers versus actual patients.	Meta analysis	Senstivity and effectiveness score when HPT done by volunteers	0.91 (95% CI: 0.84-0.96); 2.75 (95% CI:2.3-3.2) respectively	Publication bias; assessment of methodologic quality of the primary studies was not described
			Sensitivity and effectiveness score when HPT done by patients	0.75 (95% CI:0.64-0.85); 0.82 (95% CI: 0.4-1.2)

Comment(s)

Home pregnancy testing continues to be a common method for early pregnancy testing. These research studies question the clarity of positive results, false pregnancy detection as a result of early pregnancy loss, and problems with interpretation of a negative result. Currently available tests require a high concentration of hCG to be positive. They also do not effectively test for a variant of the hCG which is highly prevalent in early pregnancy. And finally, they are user dependent with accuracy worsening when performed by actual patients, with a mean sensitivity of 82%.

Clinical Bottom Line

Accuracy of home pregnancy tests in the hands of the user is low. Clinicans need to be aware of the limitations of current HPT brands.

References

1. Cole LA. et al. Accuracy of home pregnancy tests at the time of missed menses Am J Ob Gynecol 2004; 190:100-105
2. Butler SA. et al. Detection of early pregnancy forms of human chorionic gonadotropin by home pregnancy test devices Clinical Chemistry 2001;47:2131-2136
3. Bastian, LA. et al. Diagnostic efficiency of home pregnancy test kits. A meta-analysis Arch Fam Med 1998;7:465-469