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Biomedical subjects

K Spencer

Publications and source records attributed to K Spencer.

At least 145 records · Page 8Linked to original sources
PubMed1988

Antenatal diagnosis of neural tube defects using a coated bead immunoassay for acetylcholinesterase in amniotic fluid.

The development and validation of a coated bead immunoassay for amniotic fluid acetylcholinesterase is outlined. The assay has good precision (between assay CV of 6.8% within the normal range), and is linear up to 250 arbitrary units/L. The clinical validity of this assay has been assessed using a panel of amniotic fluid samples from normal and abnormal pregnancies. At an assay cut off level of 200 arbitrary units/L, all cases of neural tube defect-affected pregnancies were identified and the number of false positives was very small. False positives resulted from severe blood staining of the amniotic fluid. Since the monoclonal antibody used recognises red cell membrane acetylcholinesterase and the stored amniotic fluids had been frozen and thawed a number of times, the extent of this problem needs to be further assessed using freshly collected samples. The performance of this assay was found to be superior to the differential inhibitor colorimetric method and close to that of the electrophoretic procedure. The quantitative nature of the assay and the independence from operator technique makes it a useful adjunct to the measurement of amniotic fluid AFP in the prenatal diagnosis of neural tube defects.

Acetylcholinesterase↗
PubMed1985

Screening for Down's syndrome using serum alpha fetoprotein: a retrospective study indicating caution.

A report was made on the outcome of a four year retrospective study in 27 064 pregnancies, of the clinical efficiency, sensitivity, and specificity of a screening programme for Down's syndrome based on reported strategies related to the measurement of maternal serum alpha fetoprotein. This study identified 27 pregnancies affected by Down's syndrome with a median multiple of the median maternal serum alpha fetoprotein concentration of 0.82. This figure is considerably higher than that obtained from previous reports on this subject. With an age related multiple of the median maternal serum alpha fetoprotein strategy, 30.8% of Down's affected pregnancies were identified as well as 11.6% of unaffected pregnancies. Perhaps a United Kingdom collaborative study should begin to investigate the reasons for such wide population variance in the reports for the median multiple of the median for Down's affected pregnancies. Until such studies are carried out, screening for Down's syndrome based on low maternal serum alpha fetoprotein concentration is premature.

Adult↗
PubMed1983

The measurement of amniotic fluid alpha 2 macroglobulin by fixed time kinetic immunoturbidimetry.

We have developed an assay for alpha 2 macroglobulin in amniotic fluid, based on the technique of Fixed Time Kinetic Immunoturbidimetry. The assay is precise (CV 5% between assays) and has a detection limit of 0.4 mg/l. We have determined the reference range for alpha 2 macroglobulin from 100 amniotic fluid samples from none Neural Tube Defect pregnancies. The data indicates no significant variation of alpha 2 macroglobulin with gestational age and that the results in none Neural Tube Defect pregnancies showed a narrow reference range with a mean of 1.67 mg/l and -/+ 2 SD range of 0.23--3.11 mg/l (99 percentile = 3.65 mg/l). Results in 25 Neural Tube Defect pregnancies are presented.

Amniotic Fluid↗
PubMed1983

Immunonephelometric and immunoturbidimetric assays for proteins.

Immunonephelometric and immunoturbidimetric techniques for the measurement of proteins have developed and expanded rapidly in recent years and are fast replacing the time-honoured gel precipitation techniques. The reasons for this are primarily an increased awareness of the value of specific protein measurements with the impetus of improved chemical reagents and advances in instrument technology. This review discusses the background to such free fluid phase immunochemical measurement systems and the developments which have occurred in this field. The following topics are reviewed. (1) The theoretical background of light scattering theory as applied to the measurement of antibody-antigen complexes. (2) The nature and kinetics of the antibody-antigen reaction in fluid media and the effect of enhancing polymers. (3) The sample and antibody requirements for nephelometric and turbidimetric assay. (4) Instrumental systems for nephelometry. (5) Instrumental systems for turbidimetry. (6) Methods of establishing, assessing and monitoring nephelometric assays for specific proteins in the laboratory.

Antigen-Antibody Complex↗
PubMed1982

Improved discrimination in the detection of neural tube defects: five biochemical tests compared.

Five biochemical tests, which have been proposed as possible adjuncts to the measurement of amniotic fluid alphafetoprotein for the identification of neural tube defects, have been measured in 49 normal and 46 neural tube defect affected pregnancies. One test, the alphafetoprotein component non-reactive with concanavalin A, was ineffective in differentiating normal and abnormal. The remaining four procedures, the activity of acetyl and total cholinesterase, the concentration of alpha 2 macroglobulin and the electrophoretic identification of acetyl cholinesterase effectively separated the normal and abnormal populations. The relative merits of these four latter tests in the evaluation of false positive and false negative amniotic fluid alphafetoprotein results, as well as in liquor samples with high alphafetoprotein levels associated with abnormalities not of neural origin, are discussed.

Abortion, Missed↗
PubMed1981

Kinetic immunoturbidimetry of human choriomammotropin in serum.

The sensitivity of kinetic immunoturbidimetry as a method for the measurement of specific proteins has been shown previously to be equivalent to 1 mg of analyte per liter. We confirm this in the method for human choriomammotropin described here. A relatively large sample volume is required, which results in other components of serum influencing the immunoprecipitin reaction. The technique is shown to be precise, and results compare well with those by a commonly available radioimmunoassay. The method performs well, as judged from results obtained for assayed quality control materials and in an external quality assurance program. The method is rapid (instrument assay time 120 s per sample), automated, and economical for routine use.

Edetic Acid↗
PubMed1980

The variable influence of an alpha component in pregnancy plasma on four different assay systems for the measurement of pregnancy-specific beta1 glycoprotein.

Four methods (radioimmunoassay, electroimmunoassay, laser nephelometry and kinetic immunoturbidimetry) have been evaluated for the measurement of proteins with pregnancy-specific beta1 glycoprotein immunoreactivity. The influence of two maternal plasma proteins with different electrophoretic mobilities (alpha2 and beta1) but with similar antigenic determinants has been assessed in each assay system. The radioimmunoassay method, which utilises a homogeneous preparation of pregnancy-specific beta1 glycoprotein for the preparation of iodinated tracer, and the kinetic immunoturbidimetric assay which measures antigen-antibody complex formation over the first minute of the reaction, were both considerably more specific for the beta1 component of pregnancy specific beta1 glycoprotein immunoreactivity than the laser nephelometric or electroimmunoassay methods.

Antigen-Antibody Reactions↗
PubMed1980

Voluntary heart-rate changes mediated by muscle tension and respiration.

20 undergraduates completed heart-rate mediation treatments (isometric exercise, relaxation, hyperventilation, and hypoventilation) with and without feedback. Heart rate increased during tension, decreased with relaxation, and changed even more with feedback. During hyperventilation the heart rates were lower than during hypoventilation, and this difference was even greater during trials with feedback. This paradoxical finding was attributed to the shallowness of the breathing. Additional data from an experiment on voluntary heart-rate control (n = 31) without feedback and one with biofeedback of heart rate (n = 18) showed that subjects were following heart-rate increase and decrease instructions with altered respiration rates. These observations are interpreted as indicating that biofeedback changes in heart rate are mediated by skeletal muscle tension, respiration, and other mediating mechanisms.

Biofeedback, Psychology↗
PubMed1980

Kinetic immunoturbidimetric measurement of thyroxine binding globulin.

We describe the extension of kinetic immunoturbidimetry to measurement of low-concentration proteins in serum, specifically thyroxine binding globulin. Method performance is superior to that of currently available direct assays for this protein by radioimmunoassay or the Laurell "rocket" techniques. The assay is rapid (1-min measurement period), economical, and results compare well with those by established techniques. The technique has wide applicability to instruments with kinetic measuring ability and could provide a useful support to other non-isotopic thyroid-function tests. The assay further emphasizes the sensitivity and usefulness of kinetic immunoturbidimetry for measuring low concentrations of proteins.

Alpha-Globulins↗
PubMed1979

Kinetic immunoturbidimetry: the measurement of pregnancy specific beta 1 glycoprotein.

The extension of kinetic immunoturbidimetry to the measurement of low concentration proteins has been described using the protein pregnancy-specific beta 1 glycoprotein. The technique has a precision superior to that of all other methods currently available. The assay is rapid, cheap and compares well with other published methods. The assay further emphasises the usefulness of the technique of kinetic immunoturbidimetry.

Female↗
PubMed1979

Kinetic immunoturbidimetry: the estimation of albumin.

The applicability of commercially available antisera for use in kinetic immunoturbidimetry has been studied using the protein albumin as a simple model. The sensitivity of the kinetic immunoturbidimetric approach has been found to be comparable to published data for nephelometric systems, being able to detect concentrations of protein as low as 1 mg/l. The technique has shown to be as precise as most dye binding techniques for the measurement of albumin, producing a within batch C.V. of 1.0% and a between batch C.V. of 1.5%. The technique was found to be comparable to another immunological technique (RID). The fast assay time (30--60 sec), cost and good precision makes this the method of choice for routine albumin measurement. The extreme sensitivity of the technique of kinetic immunoturbidimetry makes the technique applicable to the estimation of a wide range of proteins in blood, urine and CSF.

Coloring Agents↗
PubMed1979

A rapid kinetic assay for glucose using glucose dehydrogenase.

An automated kinetic assay for the determination of glucose in blood is described. The method employs the enzyme glucose dehydrogenase in the presence of mutarotase, with nicotinamide adenine dinucleotide as hydrogen acceptor. The analytical parameters of the method are determined and the flexibility of the method in relation to sample volume and sensitivity is discussed. Finally, the method is compared with automated glucose oxidase and hexokinase procedures.

Autoanalysis↗