Evaluation of first trimester maternal serum and ultrasound screening for Down's syndrome in Eastern and Northern Finland.

The current trend in prenatal diagnosis is that trisomy screening is being moved to the first trimester and ultrasonographic nuchal translucency measurement is included in risk calculation. It is likely that biochemical screening in the second trimester will gradually be given up. In Eastern and Northern Finland, during the year 1999 we offered first-trimester ultrasonographic and serum screening for trisomy 21, with measurements of maternal serum PAPP-A and beta-hCG. A total of 2515 pregnant women participated in the screening, yielding the detection of eight foetuses with Down's syndrome. Six affected foetuses (75%) were detected by means of first-trimester serum screening. Since we were in the phase of collecting data for the Finnish medians for PAPP-A and beta-hCG, the women were not given the estimates of risk for trisomy 21. Only 1602 of the 2515 enrolled women had the combination of first-trimester ultrasonographic and serum screening performed, and in that group there were five foetuses with Down's syndrome. The combination ultrasonographic and serum approach yielded a Down's syndrome detection rate of 80% (four out of five) with a 5% false positive rate, whereas in nuchal translucency based-screening the detection rate was 60%, with a 5% false positive rate.

In vitro stability of free prostate-specific antigen (PSA) and prostate-specific antigen (PSA) complexed to alpha 1-antichymotrypsin in blood samples.

OBJECTIVES: To study the in vitro stability of free and complexed forms of prostate specific antigen (PSA) in blood samples in order to establish guidelines for specimen handling, in particular for the clinical utility of the analysis of percentage free PSA. METHODS: Blood samples were collected and processed to generate serum, heparin plasma, and EDTA plasma. Three different two-site immunoassays were used to measure the concentrations of total PSA (PSA-T), free form of PSA (PSA-F), and PSA-alpha 1-antichymotrypsin complex (PSA-ACT) in order to determine the effect of repeated freezing and thawing, delayed separation of serum from blood cells, and stability during storage at 4 degrees C and 30 degrees C. RESULTS: Five cycles of freezing and thawing introduced no statistically significant changes in the measured concentrations of PSA-T, PSA-F, or PSA-ACT. The effect of storing blood samples at room temperature for 1-6 h before separation of serum revealed a statistically significant decrease only for PSA-F after 5.5 h of storage (mean decrease 3.5%). PSA-T and PSA-ACT showed good stability in both serum and plasma samples, whereas PSA-F, after 1 week of storage at 4 degrees C, decreased on average by 28.8%, 7.8%, and 5.6%, respectively, in serum, heparin plasma, and EDTA plasma. The decreases of PSA-F at 4 degrees C were statistically significant (P < 0.05) relative to the controls (samples stored at -20 degrees C) after storage for 23 h in serum, 86 h in heparin plasma, and 71 h in EDTA plasma. When the same samples were stored at 30 degrees C for 24 h, only the mean decrease of PSA-F (4.8%) in serum was statistically significant. CONCLUSIONS: PSA-F in blood samples is less stable than PSA-ACT. It is not advisable to store samples on the clot, especially if time and temperature cannot be controlled. Serum samples should be stored frozen if not analyzed during the same day. After thawing, samples can be stored up to 23 h at 4 degrees C prior to analysis. The use of plasma samples improves the stability of free PSA.

Free and complexed prostate-specific antigen (PSA): in vitro stability, epitope map, and development of immunofluorometric assays for specific and sensitive detection of free PSA and PSA-alpha 1-antichymotrypsin complex.

Generation of 15 monoclonal antibodies (MAbs) allowed construction of epitope maps and specific two-site immunofluorometric assays for free prostate-specific antigen (PSA) and PSA complexed with alpha 1-antichymotrypsin (ACT). Close correlation of PSA concentrations obtained with the use of different assays of free PSA suggested extensive similarity in immunodetection of free PSA in serum. Assays of the PSA-ACT complex overestimated the concentration of PSA-ACT in serum because of nonspecific adsorbance of ACT or cathepsin G-complexed ACT to the solid phase. This interference was substantially decreased in the presence of heparin. In studying the stability of purified PSA and PSA-ACT complexes formed in vitro, we found that the free PSA was stable during storage for 4 weeks at 35 degrees C, whereas PSA-ACT complexes largely dissociated in these conditions. The instability of PSA-ACT complexes was counteracted by storage at low temperatures, by adjusting the pH of the storage buffer between 6.8 and 7.4, and through addition of 100-1000-fold molar excess of native ACT. The ease of calibration and the accuracy of free PSA assays in comparison with assays of the PSA-ACT complex suggest that measurements of free to total PSA most accurately reflect the inverse of the proportion of PSA complexed to ACT in serum.

Simultaneous assay of alpha-fetoprotein and free beta subunit of human chorionic gonadotropin by dual-label time-resolved immunofluorometric assay.

We developed a simple, rapid two-step dual-label assay for the noncompetitive determination of alpha-fetoprotein (AFP) and beta subunit of human chorionic gonadotropin (hCG beta) in serum. Monoclonal antibodies to detect AFP and hCG beta were labeled with europium (Eu) and samarium (Sm), respectively. Highly fluorescent chelates were developed by using the Delfia enhancement principle. The detection limits for AFP and hCG beta were approximately 0.02 kIU/L and approximately 0.2 IU/L, respectively. The within-run precision was < 5% over the whole range of AFP (1-500 kIU/L) and hCG beta (1-200 IU/L) concentrations tested. Cross-reaction of intact hCG was < 0.03%. The AFP concentrations determined with the dual-label assay correlated well with those obtained by Delfia AFP single-label kit. The concentrations of hCG beta were in good agreement with recently published data. Storing the serum samples for 24 h or 1 week at room temperature increased the hCG beta concentration by 4% and 26%, respectively. At 35 degrees C this dissociation of hCG increased 30-40-fold. Repeated freezing and thawing had no effect on the hCG beta concentration.

Europium-labelled streptavidin as a highly sensitive universal label. Indirect time-resolved immunofluorometry of FSH and TSH.

Labelling of streptavidin with a fluorogenic europium ion was optimized with the aim of obtaining a universal, stable and highly sensitive non-isotopic label for time-resolved fluorometric immunoassays (TR-FIA) based on dissociative fluorescence enhancement (DELFIA). Even the conjugation of all the free amino groups of streptavidin with Eu chelates had only a minor effect on the binding capacity of the protein or its affinity. The labelled streptavidin was evaluated in indirect time-resolved immunofluorometric assays of human follicle and thyroid stimulating hormones (FSH and TSH). The interassay imprecision was below 3% within the concentration range from 2.5 to 94 U/l for the FSH samples and below 5% in the range from 2.4 to 35 mIU/l for the TSH samples. The detection limits of the assays for FSH and TSH were 0.05-0.10 U/l and 0.01-0.025 mIU/l, respectively, when a CV of 15% was regarded as the acceptable upper limit of imprecision. The results obtained by the indirect assays correlated closely with those obtained by corresponding direct sandwich assays. The model assays demonstrated the utility of Eu-labelled streptavidin as a universal reagent for immunoassays requiring a wide dynamic range and high sensitivity.

Bleeding of a venous hemangioma inside the filum terminale.

Spinal vascular malformations can present with acute symptoms suggesting spinal cord or nerve root compression. We describe a case of bleeding from a venous hemangioma within the filum terminale. This malformation caused acute compression of the lumbar spinal roots. Thus, vascular malformations may exist behind the symptoms of acute radiating pain and lower extremity weakness. They can be treated by total extirpation, when possible, by resection or by decompressive laminectomy alone.

Role of glutathione in the regulation of inorganic pyrophosphatase activity in Streptococcus faecalis.

When the thiol-oxidizing agent diamide was added to a batch culture of Streptococcus faecalis during exponential growth, the specific activity of inorganic pyrophosphatase (EC 3.6.1.1) decreased to the level observed in the stationary phase. The effect of diamide was completely reversed by reduced glutathione. Furthermore, the ratio of reduced to oxidized glutathione and the specific activity of inorganic pyrophosphatase changed in a very similar fashion during batch culture. These findings, together with our earlier results, suggest that the activity of inorganic pyrophosphatase in S. faecalis is regulated by glutathione via the ratio of reduced to oxidized glutathione.