Medical screening

Details Medical screening Medical screening

2000-12-06

2003-11-25

Hindenburg, Max F. (Department: 3736)

Surgery

Diagnostic testing

C382S133000, C128S920000

Reexamination Certificate

active

06652456

ABSTRACT:

TECHNICAL FIELD
This invention relates to medical screening.
BACKGROUND
Various medical conditions are the subject of routine screening of populations of patients who are potential candidates for the particular condition. For example, in the United States women are routinely screened for cervical cancer.
Carcinoma of the cervix is one of the most common malignancies in women. Worldwide, an estimated 470,000 women develop cervical cancer each year, with more than 80% of these cancers occurring in the developing world. In general, cervical cancer progresses slowly through several well-defined stages, and thus early detection permits the cancerous lesions to be treated with nearly 100% success. The initiation of mass screening has reduced cervical cancer mortality in the United States by 50% over the last 30 years (Kavita, et al.,
Accuracy of the Papanicolaou test in screening for and follow
-
up of cervical cytologic abnormalities: a systematic review. Ann Int Med
2000; 132(10):810-819). However, many countries lack the medical infrastructure or technical expertise to carry out effective mass screening (Michelow, et al.,
Simulation of primary cervical cancer screening by the PAPNET system in an unscreened, high
-
risk community. Acta Cytol
1997; 41(1):88-92; Veneti, et al.,
PAPNET for cervical cytology screening: experience in Greece. Acta Cytol
1999; 43(1):30-33; Denny, et al.,
Two
-
stage cervical cancer screening: an alternative for resource
-
poor settings. Am J Obst Gyn
2000;183(2):383-388). As a result, cervical cancer is the leading cancer-related cause of death in women of the developing world. (Denny, et al., supra).
The standard method of cervical cancer screening uses the Pap smear, named after Dr. George Papanicolaou, who introduced it into clinical practice in the 1930s. Pap smear screening is presently a two-step process of collection and inspection. First, a physician or other trained medical professional collects a sample of cells from the cervix of the patient using an ectocervical spatula, an endocervical brush, and/or cotton swabs. Once collected, the specimen is processed by placing a portion of the sample on a dry glass slide, fixing it with a preservative, placing a cover slide on the sample, and staining it. Once the slide has been prepared and stained, it is manually screened by a cytotechnologist, under a microscope, for potentially abnormal cells. Suspicious cells may be further examined by a cytopathologist. Once a determination of the status of the sample is made, a report is produced that is normally sent to the referring physician or clinic.
There are inherent limitations in this standard screening approach related to the quality of the sample, the quality of the slide, and the effectiveness of the screener. The standard technique of placing the sampling spatula or brush on the glass slide results in capture of only the cells that are in contact with the slide. There is generally no proportional representation on the slide of all the cells taken from the cervix. In some cases, an inadequate number of cells are preserved on the slide, resulting in the need for re-screening. Even when the number of cells is adequate, the appearance of the resultant slide can be highly variable. The cells may be clumped, overlapping, and poorly preserved. Visibility may be partially obscured by blood, inflammation or drying artifacts.
There are several factors that limit the effectiveness of the slide screener. First, a typical Pap smear slide contains up to 300,000 cells. With a limited amount of time to screen each slide, the screener cannot examine each cell, but instead must do a quick overall scan of the slide and then sample the most promising areas at greater magnification looking for abnormal cells. Second, the screener must cope with habituation (the expectation of a negative result) and fatigue.
These limitations affect both the sensitivity and specificity of testing. Sensitivity refers to the proportion of cellular abnormalities that are actually detected. Sensitive tests reduce the number of false negatives—slides reported as being within normal limits when, in reality, there were cells indicative of abnormal changes. Specificity refers to the proportion of normal slides that are actually reported as normal. Specific tests have a low rate of false positives—reports of findings that require follow-up when, in fact, the smear was normal.
While the upper limit of sensitivity in Pap smear screening is 95% due to inherent sampling error (Godfrey S E,
The Pap smear, automated rescreening and negligent nondisclosure. Am J Clin Pathol
1999; 111:14-17), the actual sensitivity rate for standard screening ranges from 30-93% in the United States, with the specificity of standard screening at between 86-100% (Sprenger, et al.,
The false
-
negative rate in cervical cytology: comparison of monolayers to conventional smears. Acta Cytol
1996;40:81-89; AHCPR, Evaluation of cervical cytology.
Summary, Evidence Report/Technology Assessment: Number
5. Agency for Health Care Policy and Research, Rockville, Md. January 1999. http://www.ahrq.gov/clinic/cervsumm.htm.; Nanda, et al.,
Accuracy of the Papanicolaou test in screening for and follow
-
up of cervical cytologic abnormalities: a systematic review. Ann Int Med
2000;132(10):810-819). There is little information on quality control and therefore sensitivity outside the United States, Canada and Europe.
In addition to these technical aspects, conducting standard, manual cervical cancer screening requires a sufficient quantity of qualified cytotechnologists and cytopathologists. This quantity will determine the volume of Pap smear slides that can reasonably be screened by such trained personnel. While the Clinical Laboratory Improvement Amendment of 1988 limits the number of slides that can be reviewed in an eight-hour day to 100, such a level of productivity is highly unlikely (Rosenthal D L,
Automation and the endangered future of the Pap
test.
J Natl Cancer
Inst 1998; 90:738-749.) A more reasonable optimal number is 60 per day, while an average would be 40-50. This translates into an individual cytotechnologist having the capacity to screen 10,000-14,000 slides per year. In the United States there are approximately 4,800 certified cytotechnologists. Although there is presently a slight shortage of qualified personnel in this field, this is an adequate number to screen the 50-60 million Pap smears done every year.
However, many areas of the world lack qualified and adequately trained cytotechnologists and cytopathologists. This shortage is often a result of the lack of training infrastructure and the low reimbursement rate for such screening tests (Bartels P H.
Automation of primary screening for cervical cancer: sooner or later? Acta Cytol
1999; 43(1):7-12.) Such a situation makes it unlikely that women at risk will have adequate access to screening, or any access at all.
An example of a country in which there is such a lack of qualified cytotechnologists and cytopathologists is the United Arab Emirates. The total population of the United Arab Emirates (UAE) is approximately four million people. To screen one-third of the adult women of this country (representative of screening of every woman of screenable age once every three years) roughly 300,000 Pap smears per year would need to be done. The standard screening method would require 20-30 cytotechnologists doing nothing but Pap smears. Presently there are 15 hospitals and 15 clinical laboratories in the UAE. There are only 44 M.D. pathologists in the entire country, and very few of these are likely to be cytopathologists. While exact figures are lacking, it is reasonable to assume that, at most, only half of the hospitals and laboratories have even one cytotechnologist. Based on this assumption, at most, the UAE possesses a maximum of 15 cytology technicians. This assumption is supported by the fact that very few Pap smears are presently done in the United Arab Emirates. It is clear that this country does not have the qualified technical people t

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