P.Y. Wong

Maternal serum α-fetoprotein and fetal autosomal trisomies

Abstract Maternal serum α-fetoprotein values in 61 patients with fetal autosomal trisomies diagnosed at 6581 genetic amniocenteses were significantly lower than those in an equal number of matched control subjects. The genetic risk of fetal autosomal trisomies for women

Measurement of cyclosporine a by a specific radioimmunoassay with a monoclonal antibody and 125I tracer

We developed a sensitive radioimmunoassay (CYCLO-Trac SP) that specifically measures cyclosporine A in serum, plasma and whole blood of transplant patients. The specific monoclonal antibody was from Sandoz and the tracer was an 125I derivative of cyclosporine C. The assay is performed at room temperature for 1 h followed by a 20 min centrifugation. The sensitivities of the assays are 2.6 ng/mL and 8.7 ng/mL for the serum/plasma assay and the whole blood assay, respectively. Within-run and between-run CVs for both types of assays using cyclosporine concentrations of 80 and 58 ng/mL (serum) and 186 and 199 ng/mL (whole blood) were less than 5% and 9%, respectively. Averaged recovery of serum/plasma and whole blood assays at various levels ranged from 93% to 115%. Interferences by bilirubin, triglyceride, cholesterol, hemoglobin, OKT-3, azathioprine, methylprednisolone and 20 other drugs were insignificant. Multicenter proficiency studies showed an excellent correlation between the CYCLO-Trac SP and the specific 3H-Sandimmune assay from Sandoz: whole blood assay (r = 0.998) and serum assay (r = 0.997).

Amniotic fluid testosterone in the prenatal determination of fetal sex.

In the field of genetics, a rapid and accurate test for the prenatal determination of fetal sex, especially in cases of sex-linked disorders, is desirable. Amniotic fluid testosterone was measured by the radioimmunoassay technique in 37 samples obtained at saline abortion between 16 and 19 weeks gestation. Final confirmation of fetal sex was obtained from fetal gonadal histology. In pregnancies with male fetuses, the mean amniotic fluid testosterone value of 27.6 ng. per 100 ml. was significantly higher (p less than 0.001) than the mean value of 9.6 ng. per 100 ml. found in pregnancies with female fetuses. The range for pregnancies with male fetuses was 15.5 to 41.3 ng. per 100 ml. and for those with female fetuses 5.7 to 15.1 ng. per 100 ml. With a coefficient of variation of 5 to 8% considered for the method of assay, there was an area of potential overlap from 12 to 18 ng. per 100 ml., giving a predictive error of approximately 16%. For patients in whom the results are clearly outside the area of overlap, this test is of value as a preliminary screen in the prenatal determination of fetal sex, especially in X-linked disorders.

Amniotic fluid testosterone and follicle-stimulating hormone assay in the prenatal determination of fetal sex

Amniotic fluid testosterone was assayed by radioimmunoassay in 812 samples taken at 16 weeks gestation at the time of genetic amniocentesis. In each of 361 samples (45% of total), correct assignment of fetal sex was made where the testosterone level was above 33.8 ng/ml for male fetuses and below 16.2 ng/ml for female fetuses. In each of 159 of 353 (45%) samples assayed for follicle-stimulating hormone (FSH), levels were below 7.6 mlU/ml for male fetuses and above 10.9 mlU/ml for female fetuses. By combining the two assays in the testosterone/FSH ratio, correct assignment of sex was made in each of 282 samples (80%). The percentage of samples in which correct assignment was achieved was greater for female fetuses (ratio less than 2.2 in 161/187 [86%]) than for male fetuses (ratio greater than 3.4 in 121/166 [72%]). The testosterone/FSH ratio holds promise as a rapid biochemical screening tool in the prenatal diagnosis of fetal sex in X-linked disorders.

Amniotic fluid lecithin/sphingomyelin ratio, palmitic acid, palmitic acid/stearic acid ratio, total cortisol, creatinine, and percentage of lipid-positive cells in assessment of fetal maturity and fetal pulmonary maturity: A comparison

Lecithin/sphingomyelin (L/S) ratio, creatinine, percentage of lipid-positive cells, palmitic acid, palmitic acid/stearic acid (P/S) ratio, and total cortisol were analyzed as tests for fetal maturity and fetal pulmonary maturity in 164 samples of amniotic fluid from 121 patients. Fifty samples were taken within 72 hours of delivery. The best tests for fetal maturity (37 weeks) with differential percentages were L/S ratio, palmitic acid, and P/S ratio. In the assessment of fetal pulmonary maturity, we studied an additional 174 samples in which only L/S ratio, creatinine, and lipid-positive cells were analyzed. All tests showed a high predictive value of an immature (positive) result was much less for all six parameters; the three best tests were total cortisol (33%), lipid-positive cells (26%) and L/S ratio (14%).

Prenatal diagnosis of fetal sex by amniotic fluid testosterone and FSH, and their potential use in detecting sex linked disorders

Amniotic fluid testosterone was assayed by radioimmunoassay in 971 samples at 16-18 weeks gestation. FSH assay was performed in 353 of these samples. Correct prediction of fetal sex (46%) was made in all samples with a testosterone level above 338 ng/L for all males, and below 162 ng/L for females. For 45% of samples with FSH levels below 7.6 IU/L for males and 10.9 IU/L for females the fetal sex was predicted correctly. By using a testosterone/FSH ratio, the diagnostic accuracy was 80%. The anmiotic fluid of ten Duchenne Muscular Dystrophy carrier mothers were studied and only the sex of one case could not be predicted. The amniotic fluid testosterone and FSH assays could be used as a rapid biochemical screening method for predicting fetal sex in X-linked disorders before birth.

Quality assessment of cyclosporine monitoring by 32 Canadian laboratories

The Canadian Quality Assurance Program was initiated in June 1989, and is a voluntary program which currently encompasses all 32 laboratories involved in the measurement of cyclosporine (CsA) across Canada. Two whole blood samples from control or clinical patients (kidney, liver and heart) containing unknown concentrations of CsA are circulated to each participating laboratory monthly, and analyzed by all techniques employed within that laboratory. Four analytical methods are currently employed: HPLC (n = 4). Sandimmun SP (n = 3), CycloTrac SP (n = 27) and TDx (n = 3). Four laboratories reported survey results in more than one methodology. Results from all participating centers are analyzed monthly. The mean, SD, standard deviation index and range are reported to each laboratory with information coded to preserve confidentiality. Accuracy, precision, recovery, analytical specificity, linearity and blank studies have been performed. This report covers the period from June 1989 to April 1990.

Studies of an alpha-fetoprotein assay using dry blood-spot samples to be used for the detection of fetal neural tube defects

We modified the Pharmacia serum alpha-fetoprotein (AFP) kit to enable its use with dry blood-spots on filter paper. Reference values were established for blood from 253 women in the 16th to 18th weeks of gestation. The result by the present technique in a woman with a confirmed anencephalic fetus was elevated, and in agreement with the results of AFP assays in serum and amniotic fluid. Blood AFP was stable on dried filter paper sent by mail.

Measurement of human skeletal muscle acetylcholine receptor antibodies using monkey receptors.

Human skeletal muscle acetylcholine receptor (AChR) antibodies were assayed by a double immunoprecipitation technique using 125I-alpha-bungarotoxin as the label. Monkey AChRs were found to be superior to those from diabetic humans for analytical and practical reasons. The analytical sensitivity is 0.05 nmol alpha-bungarotoxin/L serum. The between-run and within-run precision (1 c.v.) of the assay are 13% and 3%, respectively. The normal range is 0-0.2 nmol alpha-bungarotoxin/L. There was no correlation between the antibody concentration and the clinical severity of myasthenia gravis. The clinical sensitivity and specificity of the assay for generalized myasthenia gravis are 79% and 96%, and for ocular myasthenia gravis 29% and 96%, respectively.

Comparison of two immunoassay methods for the determination of alpha-fetoprotein in amniotic fluid

We compared two immunoassay methods for determination of alpha-fetoprotein in amniotic fluid. The two methods showed a very good correlation and this is further confirmed by the clinical study. The electroimmunoassay (rocket immunoelectrophoresis) seems suitable for a small laboratory, whereas radioimmunoassay may be a better choice for a large laboratory.