Diagnostic and Screening Tests in Pregnancy
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Published: Tue, 26 Sep 2017
Jody Wellington 2153629
Screening tests are predominantly designed to discriminate between populations at high risk of developing a disease or disorder, and those that are not (Pairman, 2010). While diagnostic tests aim to establish the presence or absence of diseases and disorders (Ruf, 2008). The author has outlined below five screening and five diagnostic testing that may be investigated during pregnancy. The author will choose one screening and one diagnostic test and examine them in brief, discussing these investigations in terms of their validity and reliability. The author will also assess the validity table presented in the documented portfolio determining results for probabilities. Finally the author will discuss the Pap smear mass screening test and relate it with Wilson and Jungner’s criteria.
List five screening investigations
- Rubella status
- Blood grouping and antibody status
- Non-invasive prenatal testing (NIPT)
List five diagnostic investigations
- Dating US
- Morphology US (foetal growth and placental position)
How good are your investigations?
Morphology scan and diabetes testing
Are the test results dichotomous or non-dichotomous?
The author feels that both investigations are dichotomous. Given that any test that can result a positive or negative outcome, or one that is out of the ‘normal’ range, requires further investigation. Therefore by dividing each screen into a positive or negative result we are offering further testing if it is required.
Are there any references to measures of validity for the investigation in question?
Morphology ultrasound scanning has been proven beneficial in detecting foetal morphological anomalies (Health, 2008). First trimester ultrasounds have been beneficial in detecting major congenital heart disease (Rasiah et al., 2006). While second trimester ultrasounds have been shown to have accuracy in detecting congenital malformations, increasing diagnostic sensitivity (Chen et al., 2008).
Gestational Diabetes Mellitus has increased over the years with the increase in sedentary lifestyles poor nutritional intake prior to conception. There are many research articles available referencing the preconception lifestyle of women leading to positive OGTT (Retnakaran et al., 2009). Screening for GDM is an important aspect of antenatal care, as the development or recognition of GDM can lead to common complications such as macrosomia, birth injury, adult obesity and glucose intolerance (Santos-Ayarzagoitia et al., 2006).
Consider whether reliability of results is likely to be a problem.
When performing a morphology ultrasound by two different sonographers each person will have a personal bias opinion. However due to protocols, policies and guideline results, bias can be eliminated. The same can be said for GDM screening. With the introduction of guidelines and acceptable results, determining who is at risk and who is not can be narrowed. Thus, reducing the cost to the patient and society on obtained outcomes.
CHEN, M., LEE, C. P., LAM, Y. H., TANG, R. Y. K., CHAN, B. C. P., WONG, S. F., TSE, L. H. Y. & TANG, M. H. Y. 2008. Comparison of nuchal and detailed morphology ultrasound examinations in early pregnancy for fetal structural abnormality screening: a randomized controlled trial. Ultrasound in Obstetrics & Gynecology, 31, 136-146.
HEALTH, T. D. O. 2008. 18-22 Week Detailed Morphology Scan [Online]. Available: http://www.health.gov.au/internet/publications/publishing.nsf/Content/di-obs-guidelines0907-toc~di-obs-guidelines0907-s3~di-obs-guidelines0907-s3.4.
RASIAH, S. V., PUBLICOVER, M., EWER, A. K., KHAN, K. S., KILBY, M. D. & ZAMORA, J. 2006. A systematic review of the accuracy of first-trimester ultrasound examination for detecting major congenital heart disease. Ultrasound Obstet Gynecol, 28, 110-6.
RETNAKARAN, R., QI, Y., SERMER, M., CONNELLY, P. W., ZINMAN, B. & HANLEY, A. J. 2009. Comparison of National Diabetes Data Group and American Diabetes Association diagnostic criteria for gestational diabetes in their identification of postpartum risk of glucose intolerance. Diabetes Res Clin Pract, 85, 40-6.
SANTOS-AYARZAGOITIA, M., SALINAS-MARTINEZ, A. M. & VILLARREAL-PEREZ, J. Z. 2006. Gestational diabetes: Validity of ADA and WHO diagnostic criteria using NDDG as the reference test. Diabetes Res Clin Pract, 74, 322-8.
Known to have Chlamydia
Known to NOT have Chlamydia
Urine test positive
Urine test negative
Calculate the following:
A – 174 B – 65 C – 26 D – 735
A/(A+C) = 0.87 or 87%
D/(B+D) = 0.91 or 91%
False Positive Rate
B/(B+D) = 0.08 or 8%
False Negative Rate
C/(A+C) = 0.13 or 13%
Positive Predictive Value
A/(A+B) = 0.71 or 71%
Negative Predictive Value
D/(C+D) = 0.96 or 96%
A/(A+C) + D/(B+D) = 178%
Positive Likelihood Ratio
Sensitivity (A/(A+C) ) / FPR (B/(B+D)) = 10.87
Negative Likelihood Ratio
FNR (C(A+C) ) / Specificity (D/(B+D) ) = 0.14
- The condition sought is an important health problem.
The use of the Pap smear screening process is primarily intended to screen people of an identified target population, who do not currently show symptoms of disease progression (Victoria, 2014). The health care provider educates the woman of the importance of the screening test.
- There is an accepted treatment for patients with recognised disease.
The screening test then divides the apparently well people into two groups: a possibly diseased group and a likely healthy group (Lappen, 2012). Those with ‘positive screen results’ are then referred for fuller investigation or interventions (Victoria, 2014). These interventions aim to detect disease early, before it clinically manifests.
- Facilities for diagnosis and treatment are available.
The screening program must be cost effective (Victoria, 2014). Facilities for diagnosis and treatment must be readily available, and course of actions after a positive result must be agreed on and acceptable to those screened (Morrison, 2010) .
- There is a recognisable latent or early symptomatic stage.
The health care provider educates women on the importance of early detection through the use of regular pap smear screening. Early recognition of the disease therefore can maximise the effectiveness of treatment plans, and reduce the cost to the health system when the disease has progressed to end stage (Lappen, 2012).
- There is a suitable test or examination.
The pap smear screening appears to be the suitable screening tool for cervical changes given the fact the screen is a reliable source in identifying who is at high risk of developing the disease (Victoria, 2014). The screen is primarily used by healthy women not seeking medical advice to prevent and diagnose the disease (Victoria, 2014).
- The test is acceptable to the population.
The screening is a minimally invasive procedure designed to cause minimal discomfort to the woman (Colyar, 2015). The screen has a target audience of women and designed to initiate further testing or treatment in the event of a positive result (Victoria, 2014).
- The natural history of the condition including development from latent to declared disease is adequately understood.
Cervical cells progress through changes before becoming cancerous (Lappen, 2012). With this in mind the screening result would identify those changes and to the required treatment. However this test may provide some unsatisfactory results, with the screening sample possibly being abnormal due to collection inadequacies.
- There is an agreed policy on whom to treat as patients.
The screening process is designed to target women in a certain age group with the appropriate physical history taken (Victoria, 2014).
- The cost of case finding (including diagnosis and treatment of patients diagnosed) is economically balanced in relation to possible expenditure on medical care as a whole.
As the pap smear is a screening test the cost is relatively cheap, easy and reliable (Colyar, 2015). Following an abnormal result the cost may continue to be minimal depending on the result (Colyar, 2015). However it is important for the woman to be educated on the overall cost to herself and the health system if follow-up testing is not attended.
- Case finding occurs on a continuing process and is not a ’once and for all’ project.
On receiving results from the pap smear it is essential the woman be diligent with future screening (Victoria, 2014). The health professional is to educate the woman on continuing screening after a negative result, and also following up on screening and diagnostic procedures post positive result.
COLYAR, M. R. 2015. Advanced practice nursing procedures, Philadelphia, PA, F.A. Davis Co.
LAPPEN, J. G., D. 2012. Evidence-Based Cervical Cancer Screening: The monern Evolution of the Pap Smear. In: SITARAS, N., PROF. (ed.) Evidence Based Medicine – Closer to Patients or Scientists?
MORRISON, R. M., P. SHELTON, M. 2010. PAP SMEAR RATES: PREDICTOR OF CERVICAL CANCER MORTALITY DISPARITY? Online Journal of Rural Nursing and Health Care.
VICTORIA, P. 2014. Pap tests. Better Health Channel.
Marking Guide—MIDW9010—Assignment 3: Portfolio Module 1
The portfolio reflects the activities in each module that you were asked to complete.
Personal learning objectives (10%)
Learning objectives identified are relevant and appropriate
Topic presentation, Quality of evidence (70%)
Ideas & assertions are supported by argument & evidence
The complexities of the issue are addressed in depth
Areas to be covered
Activity 1 Developing personal reference materials
Activity 2 How good are your investigations?
Activity 3 Practising 2 x 2 tables
Activity 4 Pap smear as a mass screening tool
Written expression and presentation (10%)
Assignment submitted in correct format with cover sheet and marking guide
Correct spelling throughout
Legible, well set out work
Broad range of appropriate sources cited
Adequate acknowledgement of sources
Conforms to the University referencing style
Total Mark /100
Jody Wellington 2153629
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