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A P Schellekens

Publications and source records attributed to A P Schellekens.

15 recordsLinked to original sources
PubMed1994

Inter-laboratory external quality assessment schemes for specific IgE antibodies. The results of a European scheme for 1992.

External quality assessment programmes for specific IgE have been organised for some years in the United Kingdom, Belgium and the Netherlands but independently. This paper describes a co-operation scheme whereby the same samples were circulated simultaneously from each of the three countries and subsequent results combined to produce a single "EURO EQAS" report. Serum pools were prepared each containing antibodies, at differing concentrations, to 4 different allergens. The allergens surveyed represented the 10 most commonly encountered in Northern Europe. Results were submitted in grades (or classes) and in quantitative units and they showed some similarity by grade regardless of method used but differed greatly in units probably due to method differences. This paper shows how results could be treated to produce statistical data for the participants to help them be aware of their performance internally and also in comparison to other users.

Allergens↗
PubMed1991

[Erroneous diagnosis 'neonatal hypoglycemia' due to incorrect preservation of blood samples].

The high frequency of neonatal hypoglycaemia found in the St. Catherine's Hospital, Eindhoven [corrected], (8.2% of all newborn infants had values of 1.8 mmol/l glucose or less) promoted us to test the effects of the different conditions of blood preservation before measuring in a consecutive series of 18 newborn infants at risk for hypoglycaemia. When blood was preserved in microtest tubes coated with sodium fluoride (NaF) and measured after 1 hour at room temperature, the glucose level decreased by 7 to 36%. Storage on melting ice for one hour prevented this decline completely. In our hospital sodium fluoride coated microtest tubes are used. They were found to contain various concentrations of NaF, ranging from 0.85 to 2.65 mg/ml. In a 2nd experiment with cord blood from 8 patients, we proved that a concentration of 16 mg/ml sodium fluoride was necessary to inhibit glycolysis and to prevent a fall of plasma glucose. The rapid determination of blood glucose values, i.e. within 10 minutes after the blood sample is taken, decreased, as expected, the frequency of hypoglycaemia in the newborn at risk.

Blood Glucose↗
PubMed1981

Hormonal responses to high-dose fentanyl anaesthesia. A study in patients undergoing cardiac surgery.

The hormonal responses to anaesthesia and cardiac surgery were studied in 20 patients. Ten patients were anaesthetized with fentanyl 60 microgram kg-1 and nitrous oxide in oxygen and 10 with etomidate 0.3 mgkg-1 and nitrous oxide in oxygen plus halothane. There were no significant changes in cortisol, growth hormone or insulin concentrations in response to surgery in either group, although cortisol concentrations decreased during cardiopulmonary bypass. Both groups showed increases in prolactin concentrations. Patients anaesthetized with etomidate and halothane showed a significant increase in adrenaline and glucose concentrations not seen in the fentanyl group. Cardiopulmonary bypass was associated with marked increases in catecholamines in both groups.

Aged↗
PubMed1981

Assay of glycosylated haemoglobin using agar electrophoresis.

A fast electrophoretic method for measuring glycosylated haemoglobin (HbA1) is described. Eight samples per cell can be assayed in a single run. Results are compatible with those found by macro-column cation-exchange chromatography; precision is good. The practical short-comings of the commercially ready-made mini-column chromatographic procedures are not seen using this method.

Chromatography, Ion Exchange↗
PubMed1981

Sources of variation in the column-chromatographic determination of glycohemoglobin (HbA1).

We studied the influence of many variables on the cation-exchange chromatographic determination of glycohemoglobin was minicolumns (HbA1) and with macrocolumns (HbA1a+b and HbA1c). Minicolumns are most sensitive to buffer composition. The best conditions are pH 6.78 and sodium, potassium, and phosphate concentrations of 54.8, and 36 mmol/L, respectively. In fact, there is no clear cut-off point for elution. A cyanide concentration of 1.5 mmol/L has no negative effects. For macrocolumns, the influence of temperature is demonstrated; 20 degrees C is optimal. A higher temperature caused results for HbA1 to be higher. For minicolumns, the temperature effect corresponds to 1% HbA1 per 1 degrees C, necessitating rigorous temperature control. The amount of sample applied also influences the results. Therefore a constant column load, chosen between 1.3 and 2.0 mg of Hb permilliliter of resin, is advised. Heparinized blood can be kept for three days at 4 degrees C; hemolyzed samples are best stored at -70 degrees C.

Chromatography, Ion Exchange↗
PubMed1980

The value of an intravenous TRH test for the diagnosis of tumoural prolactinaemia.

The plasma Prl response to 200 micrograms TRH iv was evaluated in 6 hyperprolactinaemic women without radiological evidence of a pituitary tumour (group I), in 15 hyperprolactinaemic women with dubious (group II) and in 17 normo- or hyperprolactinaemic women with clear (group III) radiological abnormalities, in 18 normo- or hyperprolactinaemic men with clear radiological abnormalities (group IV), and in 4 women and 3 men with hyperprolactinaemia and sellar destruction who had been treated in the past for pituitary adenoma (group V). The responses were compared with those obtained in a control group of 83 (42 women, 41 men) normoprolactinaemic healthy individuals. The Prl response was defined as a ratio (R2): the 20 min value minus the 0 min value, divided by the 0 min value. The median R2 values were: female controls 5.1, male controls 3.1, group I 0.1, group II 0.2, group III 0.3, group IV 0.55, group V females 0.45 and males 0. It is concluded that 1) subjects suspected of harbouring a microprolactinoma (groups I and II) demonstrate absent or attenuated responses similar to those found in patients with definite prolactinomas and 2) a value of plasma Prl 20 min after 200 micrograms TRH iv greater than 3.5 times the basal level (R2 > 2.5) rules out the presence of a prolactinoma.

Adenoma↗
PubMed1978

Protein hormones in cerebrospinal fluid: evidence for retrograde transport of prolactin from the pituitary to the brain in man.

Plasma and cerebrospinal fluid (CSF) levels of two hormones of similar molecular size, pituitary prolactin (PRL) and human chorionic somatomammotropin (hCS), and of the bigger hormone human chorionic gonadotropin (hCG) were measured in six pregnant women without pituitary disease. For all three hormones, the plasma and CSF levels were closely correlated. The plasma/CSF concentration ratio for hCG (571 +/- 378, mean +/- SD) was significantly different (P less than 0.01) from the hCS ratio (24.6 +/- 6.1); the hCS ratio was significantly different (P less than 0.005) from the PRL ratio (7.2 +/- 1.5). We conclude that (1) the CSF concentration of a protein hormone depends on the plasma concentration and on its molecular size, and (2) pituitary hormones reach the CSF not only via filtration of peripheral blood at the choroid plexuses, but also more directly via retrograde transport from the pituitary to the brain.

Biological Transport↗
PubMed1978

Modulation of gastrin release by acute changes in plasma calcium.

Gastrin release was studied in 5 hypergastrinemic patients, both during calcium infusion and EDTA infusion. In each patient, gastrin decreased in conjunction with the fall in plasma calcium, and increased during calcium infusion. Plasma gastrin and calcium levels were strongly correlated.

Achlorhydria↗
PubMed1978

Prolactin in human cerebrospinal fluid.

PRL was measured radioimmunologically in plasma and cerebrospinal fluid (CSF) samples obtained simultaneously in 31 patients with various neurological or infectious, but non-endocrine diseases (group A), 12 patients (7 pregnant women and 5 newborns) with physiological hyperprolactinemia (group B),10 psychiatric patients with pharmacologically induced hyperprolactinemia (group C) 12 normoprolactinemic patients with pituitary adenoma and suprasellar extension (SSE) (group D), And 14 hyperprolactinemic patients with pituitary adenoma with and without SSE (group E). Plasma PRL and CSF PRL concentrations (ng/ml, mean and range in brackets) of the various groups were: group A, 6.2 (1.3-14.5) and 1.3 (0.6-4.7); group B, 85.2 (31-200) and 13.2 (3-28); group C, 54.3 (3.5-160) and 6.5 (0.7-18); group D, 17.2 (5.4-30) and 9.7 (2.7-34); and group E, 2,529 (115-10,000) and 1,449 (6-13,000). The plasma to CSF concentration ratios (mean and range in brackets) were: group A, 5.2 (1.4-13.0); group B, 7.0 (2.9-10.3); group C, 7.3( 3.9-11.3); group D, 2.6 (0.9-7.1); and group E, 10.9 (0.2-34.9). The ratio was greater than 3 in 87% of the non-tumor patients; in 42% of the tumor patients the ratio was less than 3. The correlation between plasma and CSF PRL levels of all 53 subjects without a pituitary tumor (groups A, B, and C) was positive (r=0.9097; P=0.00001); in the 26 tumor patients (groups D and E) the correlation was also positive (r=0.7141; P=0.00002). These results indicate that 1) PRL is a normal constituent of CSF, 2) the CSF PRL level is a function of the plasma level, 3) detectable, or even high, CSF PRL levels per se are not indicative in the presence of a pituitary tumor, with or without SSE, and 4) abnormally low ratios may be found in patients with a pituitary tumor with SSE.

Adenoma↗
PubMed1974

Original articles.

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Adenoma, Chromophobe↗