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Calculation of sensitivity of primary screening
Variables for use with listed formulae:
| Final smear report | ||||
| Abnormal | Normal | |||
| HSIL+ | ASCUS/LSIL | Negative/Inadequate | ||
| Cervical smear report prior to QC check | Abnormal | a | b | c |
| Normal | d | e | f | |
Sensitivity of primary screening= abnormals identified correctly before QC check / abnormals identified after QC check x100
Overall sensitivity of primary screening= a + b / a+b+c+d x 100
Sensitivity of primary screening for HS I L+ = a+f / a+d x 100
Definition of sensitivity and specificity
Sensitivity: The sensitivity of the test is defined as the proportion of subjects with the disease correctly identified as positive out of all persons (tested) with the disease
Specificity: The specificity of a test is defined as the rate of correctly identified persons without disease in relation to all persons (tested) without disease
Method of calculation of sensitivity and specificity and false negative rate of the cervical smear test (Pap test) using histology as the gold standard
| Pap test | Outcome | |
| Positive | Negative | |
| Positive | True positive Pap test (A) | False Positive Pap test (B) |
| Negative | False negative Pap test (C) | True positive Pap test (D) |
| Sensitivity= | A / A+C | True Positive / True Positive + False Negative |
| Specificity = | D / D+B | True Negative / False Positive + True Negative |
False negative rate = 1- sensitivity
False positive rate = 1- specificity
Method of calculation of Positive Predictive Value & Negative Predictive Value using Histology as the Gold Standard
| Positive predictive value | A / A+B |
| Negative predictive value | C / C+D |
The PPV of a Pap test reflects the accuracy with which an abnormal smear result predicts cervical neoplasia. The NPV of a Pap test reflects the accuracy with which a negative smear result predicts absence of disease.
Predictive values depend on the prevalence of CIN & cervical cancer in the population. The predictive values will vary according to whether the population screened are at high risk or low risk of cervical cancer.