A COMPARISON OF COLPOSCOPY AND PAPANICOLAOU SMEAR : SENSITIVITY,SPECIFICITY AND PREDICTIVE VALUE
Sukhpreet L Singh*, Nayana A Dastur**, Murari S Nanavati***
D*Family Planning Officer; **Honorary Professor and Head of Unit; ***Honorary Associate Obstetrician and Gynaecologist, Nowrosjee Wadia Maternity Hospital, Seth GS Medical College, Mumbai.
A total of 100 patients between the ages of 18 and 63 years were screened for cervical intraepithelial neoplasia and invasive cervical cancer by simultaneous Papanicolaou smears and colposcopy. The accuracy of each screening test, when positive or suspicious, was evaluated independently and the results compared with colposrnpically directed biopsy results. Colposcopy was more sensitive than the Papanicolaou smear, whereas the Papanicolaou smear was more specific than colposcopy in detecting cervical intraepithelial neoplasia.
The Papanicolaou (Pap) smear is the primary screening tool for cervical intraepithelial neoplasia (CIN) and inva sive cancer of the uterine cervix. Use of the Pap smear has reduced morbidity and mortality from invasive cancer in various population groups., Recently, the assumed accuracy of the Pap smear, 80 to 95% for detecting CIN and early invasive cancer, has been questioned. Conversely, a false negative rate of the Pap smear has b en~eported under carefully controlled condition.[6-10]The si multaneous use of cytological studies and screening colposcopy has been shown to increase cervical cancer detection.
MATERIAL AND METHODS
This prospective study compared the Papanico smear with the colposcopic findings in ring for cervical intraepithelial neoplasia and ave cervical cancer. A total of 100 patients between the ages of 18 and 63 years who had symptoms such as chronic leucorrhoea, postcoital bleeding, intermenstrual bleeding, or the findings of erosion, an unhealthy cervix, a lesion bleeding on touch, or an abnormal or suspicious Papanicolau smear were included in this study. Colposcopy was performed using the Leisgang model. All patients underwent both acetic acid and Schiller's test before subjecting them to colposcopic directed biopsy. The colposcopic findings were classified according to the nomenclature into:
Patients with a suspicious or positive Papanicolaou smear or colposcopy were further subjected to biopsy. Records of all the patients were maintained and their colposcopic picture was drawn using Hammond's graph.
RESULTS AND ANALYSIS
The study consisted of 100 patients, in whom there were 48 with suspicious colposcopic findings and 11 had positive Papnicolaou smears (Table 1). In the same patient group, 19 cervical intraepi-thelial neoplasia lesions were detected by colposcopy and four were detected by the Papani-colaou smear. Thus, 4.75 times more cervical intraepithelial neoplasia lesions were detected by colposcopy than by the Papanicolaou smears.
Nineteen patients had cervical intraepithelial neoplasia lesions detected by colposcopically di-rected biopsies. Of 51 patients who had positive screening tests (positive Papanicolaou smears, sus-picious, colposcopy or both), I1 had positive Papanicolaou smears, 7 (63.6%) of which showed no dysplasia at colposcopically directed biopsies, where 48 had suspicious colposcopic findings, 29 (60.4%) of which had negative results at colposcopy.
Using the same data, we calculated the percent-age of positive or suspicious tests confirmed by biopsy (Table 2). For example, of the 2 (16.7%) of 12 women with cervical intraepithelial neoplasia one was correctly diagnosed by the Papanicolaou smear, whereas colposcopy correctly identified 11 (91.7%) of these women. Of 36 women with dys-plasia, 29 had disease incorrectly identified by colposcopy. Among the total study group of 100 women, colposcopic directed biopsy evaluation was not done in 49 women with negative Papanicolaou smears and colposcopic examinations, because we would have expected the biopsy specimens to be negative. Thus, the 96.6% figure is an artifact, which could be much lower if we had obtained negative specimens for all participants. Three women had positive or suspicious screening by both the Papanicolaou smear and colposcopic examination and subsequent biopsies (Table 3). In these women, the two screening methods were equally effective. Seventeen women had positive biopsy results and screening tests that differed. Sixteen with positive colposcopic findings and negative Pap smears, and one with a positive smear and negative colposcopic examination. Colposcopy thus proved to be more sensitive than the Papanicolaou smear for detection of cervi-cal intraepithelial neoplasia.
TABLE 1 Colposcopically directed biopsies for patients with either positive Papanicolaou smear or suspicious colposcopy Tissue diagnosis Positive Pap smear Suspicious colposcopy No. of patients No dysplasia 7 29 31 CIN 1 2 11 12 CIN 2 1 6 6 CIN 3 1 2 2 Total 11 48 51 Total no. of CIN lesions 4 19 20
TABLE 2 Percentage of colposcopically directed biopsies for patients with positive or suspicious screening Tissue diagnosis Positive Pap smear(%) Suspicious colposcopy(%) No dysplasia 23 96.7 CIN 1 16.7 91.7 CIN 2 16.7 100 CIN 3 50 100
TABLE 3 Agreement of Papanicolaou smear and colposcopy with colposcopic directed biopsy Tissue diagnosis Pap +ve,Colposcopy S Pap -ve, Colposcopy S Pap +ve,Colposcopy -ve CIN 1,2,3 3 16 1 No dysplasia 5 24 2 Total 8 40 3 S = suspicious
TABLE 4 Papanicolaou smear Pap smear Histopathology +ve Histopathology -ve Total Positive 4(a) 7(b) Negative 16(c) 73 Total 20 Sensitivity = a/ (a+c) = 4/ (4+16) = 20%
Specificity = d/ (b+d) = 73/ (7+73) = 91.25%
Predictive value = a/ (a+b) = 4/ (4+7) = 36%
False Positive rate = b/ (a+b) = 7/ (4+7) = 63.64%
False Negative rate = c/ (c+d) = 16/ (16+73) = 17.98%
TABLE 5 Colposcopy Colposcopy Histopathology +ve Histopathology -ve Total Positive 19(a) 29(b) 48 Negative 1(c) 51(d) 52 Total 20 80 100 Sensitivity = a/ (a+c) = 19/ (19+1) = 95%
Specificity = d/ (b+d) = 51/ (29+51) = 63.75%
Predictive value = a/ (a+b) = 19/ (19+29) = 39.58%
False Positive rate = b/ (a+b) = 29/ (19+29) = 60.42%
False Negative rate = c/ (c+d) = 1/ (1+51) = 1.92%
TABLE 6 Incidence of a positive Papanicolaou smear Series Incidence Koss 6.5 Neghbor and Newman 15 Sandmine et al 8.6 Tawa et al. 11.9 This study 11 (Data expressed per thousand women years).
The sensitivity and specificity of both the screening tests were calculated. As shown in Tables 7 and 8, colposcopy was more sensitive (95%) than the Papanicolaou smear (20%), whereas its specificity was only 63.75% compared to 91.25% of the Papanicolaou smear.
The predictive value of both the tests were comparable, i.e., 36% for Pap smear and 39.58% for colposcopy.
The false negative rate for colposcopy was only 1.92% compared to 17.98% for Pap smear, whereas the false positive rates were almost the same for both the tests in this study.
Colposcopy, a clinical method of proved accu-racy, is an excellent means of evaluating abnormal cervical cytology. Fortunately, colposcopic examination is satisfactory in nearly all young patients who most need conservative treatment.
At our hospital, approximately 3,800 Papanicolaou smears are done every year, and our incidence of positive smears is approximately 11 per 1,000 women, which is comparable to that in other series.
We compared the detection rate of cervical in-traepithelial neoplasia by colposcopic directed biopsies and Papanicolaou smears. A ratio of 4.25:1 was seen with the colposcopy/Pap smear, which is similar to that seen in the study done by Tawa et al.
The population screened in this study varied in age and parity, with no preference for any specific group.
The percentage of CIN diagnosed by the Pap smear was approximately 16% for CIN 1 and 2 which is similar to that detected in the study by Veridiana et al .
Also, the accuracy of colposcopic directed biopsy in this study varied from 91.7% to 100% (for CIN 1 and CIN 2, respectively), which is comparable to the detection rate of 93% in the study done by Veridiano et al. .
Colposcopic directed biopsy proved to be more sensitive (95%), but less specific (63.75%) com- pared to the Papanicolaou smear. The predictive value of both tests were similar (36% and 39.58%).
The false positive rate of colposcopy (63.64%)was similar t0 that of the Papanicolau smear (60.42%), whereas the false negative rate was significantly lower for colposcopy (1.92%) as compared to that for the Papanicolau smear.
In a study by Stafl et al , of the 136 patientswith dysplasia or carcinoma diagnosed bycolposcopically directed biopsy, in 91.2% bothCOIpOSCOpiC and cervicography findings were suspicious, whereas 2.9% were detected by cervicography in whom colposcopic findings were negative. Also 5.9% were detected by COIpOSCOpy,in whom cervicography findings were negative or unsatisfactory.
Staflx--f '13 has also demonstrated in another study that there is no significant difference in thediagnostic accuracy between cervicography andcolposcopy in patients with abnormal cervical smears; approximately 9% of cervices which were negatlVe by CerVlCOgraphy were abnormal byCOIpOSCOpy, and 8% Of COIpOSCOpiCally negativecervices were suspect by cervicography.
Earlier diagnosis Of CIN and of invasive cervi cal cancer in the adult woman is a desirable goal.CIN lesions and early invasive cancers areasymptomatic. Development of an accurate screening tool is important because earlier diagno- sis should enable us to use more conservative smear treatment, resulting in more cost effective health care.
Our findings in this prospective study show that colposcopy is definitely more sensitive than the Papanicolaou smear as a screening tool for CIN. - More than four times as many CIN lesions were identified by colposcopy than with Papanicolaou smears. The Papanicolaou smear was however more specific as a screening tool for CIN than was colposcopy.
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