Biomedical subjects
Publications and source records attributed to S E Linkins.
Data are presented to show that human chorionic gonadotropin (hCG) in urine can be detected early in pregnancy by simple immunoassays performed prior to or around the time of the expected but missed menstrual period. Differences between the use of simple immunoassays with urine and radioimmunoassays and radioreceptor assays with serum are discussed.
Drawing a line more intelligently for AFP data means using as a denominator two fairly well-defined populations (abnormal and normal), instead of one ill-defined normal population. The line is drawn at the intersect between two curves to minimize the error of misclassification; this replaces an arbitrarily defined cutoff level (multiples of the standard deviation unit). Moving the line to the right reduces the false positive error when screening for NTD, whereas moving the line to the left provides a sensitive alert signal for routine screening of maternal sera by AFP determinations for fetal distress. Adjustment of the line for cost and benefit factors and the use of probability statements that include the prevalence of specific conditions all help sharpen medical classification and decisions. Cross-sectional analysis is separated from longitudinal analysis. A benefit from this discussion may be the replacement of the normal range with a simple plot of AFP results or a percentile distribution, which would be more meaningful and more easily understood by all.
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The experience with a new, simple, and sensitive capillary tube pregnancy test requiring no refrigeration is described. The results of this test and other tests are compared against histologic results. The 1/2 unit capillary test, defined as having a sensitivity of 0.5 I.U. of HCG per milliliter, had a higher percentage of agreement with histopathologic results (99.65 per cent) than all other tests studied. The false-positive rate was 0.07 per cent and the false-negative rate was 0.28 per cent. In this series of 1,486 tests, 21 cases of pregnancy, identified by a 1/2 unit test, were missed by one or two unit tests. The earliest detection of pregnancy by the 1/2 unit capillary test confirmed by histology was 3 weeks from the last menstrual period (four cases).
Despite all the information about AFP presented, a great deal still needs to be discovered especially in pregnancy. Geographical and racial differences remain to be elucidated. Similarly, differences in obstetric population in Helsinki and Baltimore, for example, are only now being studied. Sex differences may exist; Lardinois and associates195 cited a higher level of AFP in male than female fetuses. The important questions that need to be answered are whether AFP assays can help improve the other half of prenatal care- that directed to the fetus- and whether the AFP model can help enhance our understanding of the similarities and differences of fetal and cancer cells.