Biomedical subjects

C W Weykamp

Publications and source records attributed to C W Weykamp.

7 recordsLinked to original sources

PubMed1995

Vitamin C and glycohemoglobin.

Three groups of 10 age- and sex-matched nondiabetic volunteers took 0, 750, or 1500 mg of vitamin C each day for 12 weeks. Glycohemoglobin (GHb) was measured by HPLC, electrophoresis, affinity chromatography, and immunoassay at baseline (-4 weeks and -1 day), during supplementation (6 weeks and 12 weeks), and after supplementation ended (6 and 12 weeks). Plasma vitamin C increased twofold during supplementation but, in contrast with the results of Davie et al. (Diabetes 1992; 41:167-73), there were no between-group differences in GHb, glucose, and fructosamine concentrations. Fructosamine may have increased with storage time. The net effects of vitamin C on absolute GHb at 12 weeks vs -1 day (and at 12 weeks vs 12 weeks after) in % GHb amounted to: HPLC -0.035 (-0.050); electrophoresis +0.005 (+0.035); affinity chromatography -0.070 (+0.015); and immunoassay -0.110 (+0.025). We conclude that supplementation of nondiabetics with 750 or 1500 mg of vitamin C daily for 12 weeks does not cause interference in GHb determinations by HPLC, electrophoresis, affinity chromatography, or immunoassay, and does not reduce in vivo Hb glycation.

Adult↗

PubMed1995

Standardization of glycohemoglobin results and reference values in whole blood studied in 103 laboratories using 20 methods.

We investigated the effect of calibration with lyophilized calibrators on whole-blood glycohemoglobin (glyHb) results. One hundred three laboratories, using 20 different methods, determined glyHb in two lyophilized calibrators and two whole-blood samples. For whole-blood samples with low (5%) and high (9%) glyHb percentages, respectively, calibration decreased overall interlaboratory variation (CV) from 16% to 9% and from 11% to 6% and decreased intermethod variation from 14% to 6% and from 12% to 5%. Forty-seven laboratories, using 14 different methods, determined mean glyHb percentages in self-selected groups of 10 nondiabetic volunteers each. With calibration their overall mean (2SD) was 5.0% (0.5%), very close to the 5.0% (0.3%) derived from the reference method used in the Diabetes Control and Complications Trial. In both experiments the Abbott IMx and Vision showed deviating results. We conclude that, irrespective of the analytical method used, calibration enables standardization of glyHb results, reference values, and interpretation criteria.

Calibration↗

PubMed1994

Hemoglobins S and C: reference values for glycohemoglobin in heterozygous, double-heterozygous and homozygous subjects, as established by 13 methods.

Glycohemoglobin (gly-Hb) reference ranges of non-diabetic adults with HbAA (n = 17), HbAS (n = 37), HbAC (n = 22), HbSC (n = 8), HbSS (n = 6) and HbCC (n = 3) were determined by 13 methods, based on affinity chromatography, HPLC, electrophoresis and immunoassay. Gly-Hb of subjects with HbAS and HbAC can be measured without major difficulties by most methods. Some give rise to absolute gly-Hb differences > or = 1% compared with subjects with HbAA. Measurement of HbA1c/total Hb cannot be recommended. Some HPLC and immunoassay methods cannot measure gly-Hb in subjects with HbSC, HbSS and HbCC, whereas others may suffer from interference. Most methods showed low gly-Hb, reflecting increased erythrocyte turnover. Use of special reference ranges requires previous knowledge of the condition (affinity chromatography and immunoassay) or separation of gly-Hb and its precursor Hb (HPLC and electrophoresis). Interpretation is, however, not recommended because of the numerous factors that determine erythrocyte turnover.

Adult↗

PubMed1993

Influence of hemoglobin variants and derivatives on glycohemoglobin determinations, as investigated by 102 laboratories using 16 methods.

Influences of hemoglobin (Hb) variants (HbSS, HbCC, beta-thalassemia, HbAE, HbAS, HbAC, hereditary persistent HbF) and Hb derivatives (carbamylated- and acetylated-Hbs, Schiff base, and those formed in stored blood) on results of glyco-Hb assays by 102 laboratories using 16 different methods were investigated. Affinity chromatography shows deviating results only with homozygous Hb S and C. Correct interpretation of results from patients with decreased erythrocyte half-lives requires previous knowledge on this condition. Measurements of HbA1c by HPLC and electrophoresis are obviously unsuitable for homozygous hemoglobinopathies; for heterozygous hemoglobinopathies and Hb synthesis variants, HbA1c should be expressed as percentage of HbA0 + HbA1c; abnormal Hbs are usually recognized; both carbamylated- and acetylated-Hbs interfere and Schiff base must be eliminated. Except for stored blood, all Hb variants and derivatives gave erroneous results with disposable ion-exchange columns. Dako's immunoassay is not affected by Hb derivatives; glycated Hb variants are not recognized as glyco-Hb and percentages are consequently too low. Glyco-Hb by the immunoassay of Bayer (performed by one laboratory) is not affected by Hb variants and derivatives.

Chemistry, Clinical↗

PubMed1989

Steroid profile for urine: reference values.

We describe a project, participated in by 24 institutions in The Netherlands and Belgium, to determine normal reference values for steroids in urine by capillary gas chromatography. Urine samples from 288 healthy volunteers were analyzed in triplicate. Reference values, expressed in mumol/24 h, were determined for androsterone, etiocholanolone, dehydroepiandrosterone, 11-keto-androsterone, 11-keto-etiocholanolone, 11-hydroxyandrosterone, 11-hydroxyetiocholanolone, pregnanediol, pregnanetriol, 11-desoxytetrahydrocortisol, tetrahydrocortisone, tetrahydrocortisol, allo-tetrahydrocortisol, and 17-keto- and 17-hydroxysteroids. We also determined reference ratios for etiocholanolone/androsterone, tetrahydrocortisone/tetrahydrocortisol, and tetrahydrocortisol/allo-tetrahydrocortisol; an upper limit of a discriminant function to establish polycystic ovarian disease; and reference values for 24-h urine volume and creatinine excretion. Reference values were determined separately for men and women, each in six age categories: 0-3 months, 4 months-12 years, 13-16 years, 17-50 years, 51-70 years, and older than 70 years. We conclude that these reference values are reliable and form a basis for quantitative interpretation of steroid profiles.

Adolescent↗

PubMed1985

Steroid profiling--an update.

Extraction of steroids from urine with C18 solid-phase extraction cartridges results in an extract containing impurities. If, during the extraction of hydrolyzed urine, an amino (NH2) column is placed in series with the C18 column, then one obtains a sample that is sufficiently clean for gas-chromatographic analysis. Analytical recovery of dehydroepiandrosterone from urine is considerably decreased by the use of increasing amounts of Helix pomatia enzyme preparation. Extraction of the steroid conjugates from urine with C18 columns before the hydrolysis stage is essential for hydrolysis with an amount of enzyme preparation that suffices for complete splitting of the polar steroid conjugates but not so much as to cause insufficient analytical recovery of dehydroepiandrosterone.

Animals↗

PubMed1982

Mechanism and speed of reactions between haemoglobin and glucose consequences for the measurement of glycosylated haemoglobins in patient material.

The mechanism of the reactions between haemoglobin and glucose in the erythrocyte was investigated in vitro using 14C-labelled glucose. Reaction speed constants were found for the formation of HbA1c (4.2 . 10(-3) and the formation and degradation of the Schiff Base (9.22 . 10(-4) and 0.435, respectively) for concentrations in mmol/l and time in hours at 37 degrees C. An equilibrium constant of 2.12 . 10(-3) was found for the reversible formation of the Schiff Base. The results were included in a mathematical model with which a number of clinically relevant situations were simulated. From the results the conclusion was drawn that during the measurement of fast haemoglobins, the intermediate Schiff Base causes a variation dependent on the glucose concentration at the moment of blood sampling. The model demonstrates that this disturbance can be eliminated by incubating erythrocytes with physiological saline for 10 h at 37 degrees C.

Blood Glucose↗