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R R Little

Publications and source records attributed to R R Little.

At least 37 records · Page 2Linked to original sources
PubMed1992

Interlaboratory standardization of measurements of glycohemoglobins.

The diversity of methods used to measure glycohemoglobins (GHb) makes it difficult to compare patients' results among laboratories. We reported previously the feasibility of providing comparable results from different assays by use of common calibrators. We here compare results from seven different GHb methods calibrated by use of hemolysates assayed by a precise ion-exchange high-performance liquid-chromatographic (HPLC) method for hemoglobin A1c (HbA1c). Thus, regardless of the GHb species measured by the seven methods, results were referenced to the HbA1c content of the calibrators. Without this calibration, GHb values for single samples varied, e.g., from 4.0% to 8.1% and from 10% to 14.2% in the normal and high ranges, respectively. Calibration decreased between-method variability (single sample ranges of, e.g., 4.8% to 5.4% and 9.4% to 10.2% in the normal and high ranges, respectively) and improved interassay precision. We conclude that this approach to calibration of GHb measurements allows direct comparison of results obtained by different methods and improves precision.

Calibration↗
PubMed1991

Interlaboratory comparison of glycohemoglobin results: College of American Pathologists Survey data.

We describe recent changes in the College of American Pathologists Glycohemoglobin (gHb) Survey, made to improve the assessment of interlaboratory variability and the accuracy of results reported. The questionnaire portion of the survey was revised to include an updated list of current methods, and results for survey specimens were grouped according to the component measured (Hb A1, Hb A1c, or total gHb). The survey specimen material was changed to a material thought to give more reliable results with all available methods. After these changes, instituted in 1989, between-laboratory CVs decreased for some methods. Furthermore, gHb values between method types were more consistent with results obtained from fresh blood samples under very controlled laboratory conditions. However, these recent data also show that the interlaboratory variability is still quite high for some methods and that the variability within and between method types is still very great. We describe a pilot standardization program for gHb measurement.

Chromatography, Affinity↗
PubMed1990

Lack of relationship between glucose tolerance and complications of pregnancy in nondiabetic women.

Recent studies suggest that gestational diabetes mellitus (GDM) is underdiagnosed. To test this hypothesis, we examined the relationship of perinatal complications to glucose tolerance during the third trimester. Our population consisted of 287 women evaluated at approximately 28 wk gestation who had normal fasting (less than 5.9 mM) and 2-h (less than 9.2 mM plasma glucose) levels after a 100-g glucose load. Glycosylated hemoglobin and glycosylated plasma protein were also measured. Study subjects were stratified into three groups based on 2-h plasma glucose values: group 1 (n = 59) less than 5.6 mM, group 2 (n = 112) 5.6-6.0 mM, and group 3 (n = 116) 6.7-9.2 mM. There were statistically significant but low correlations (r less than 0.20) between 2-h plasma glucose levels and mother's age, body mass index, infant weights, and Apgar scores. There was a significant increasing trend in the proportion of overweight and obese women from groups 1 to 3 (P less than 0.02). There was also a significant trend toward higher birth weights (P = 0.013) and larger proportions of large for gestational age (LGA) babies (P = 0.02) from groups 1 to 3, and women with LGA infants showed higher fasting and 2-h plasma glucose levels than women with non-LGA infants (P = 0.032). However, there was no significant difference in perinatal complications or infant morbidity or mortality between groups. Percentage of glycosylated hemoglobin or glycosylated plasma protein did not differ between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1988

Relationship of glycosylated hemoglobin to oral glucose tolerance. Implications for diabetes screening.

The oral glucose tolerance test (OGTT) for diagnosis of diabetes is inconvenient and requires a great deal of patient cooperation. Glycosylated hemoglobin (GHb), an index of long-term glycemic control, could offer several practical advantages over the OGTT for diabetes screening. We evaluated GHb as a screen for diabetes in 381 adults from a population with a high prevalence of non-insulin-dependent diabetes (Pima Indians). All individuals underwent a standard OGTT (75 g) and were separated into one of three groups: normal (N), impaired glucose tolerance (IGT), or diabetes mellitus (D) based on World Health Organization criteria. HbA1c, a GHb, was measured by highly precise high-performance liquid chromatography (interassay C.V. less than 4%). The normal range for HbA1c was 4.07-6.03% based on the 95% confidence interval for a nondiabetic, mostly Caucasian population. Compared with OGTT, HbA1c was highly specific (91%); an elevated HbA1c usually indicated D or IGT (sensitivity = 85 and 30%, respectively). A normal HbA1c did not, however, exclude a diagnosis of D or IGT. Based on previous epidemiological studies relating plasma glucose to chronic diabetic complications, GHb as measured in this study would properly identify the vast majority of subjects at risk. Long-term studies are necessary to determine the actual risk of complications in individuals with persistently normal HbA1c and D or IGT (based on OGTT).

Adolescent↗
PubMed1986

Collection of blood on filter paper for measurement of glycated hemoglobin by affinity chromatography.

We present data on a filter-paper collection and assay method for measurement of glycated hemoglobin (gHb). Onto filter paper dipped into a solution of glucose oxidase (EC 1.1.3.4) and allowed to dry, approximately 20 microL of capillary blood was spotted. For analysis, we eluted the dried blood spot from the paper by soaking in water for 1 h, then measured the gHb in the eluate by affinity chromatography. Because the gHb significantly increased from day 1 to day 14 of storage, it was necessary to standardize the day of elution from the paper. We found a high correlation between gHb measured from samples stored for 14 days on treated paper and gHb measured by affinity chromatography from frozen whole blood or hemolysates (r = 0.96). This method is convenient, requiring small amounts of blood and little sample handling and assay time, and may be particularly useful in certain situations such as large-scale screening for diabetes.

Blood Specimen Collection↗
PubMed1986

Interlaboratory standardization of glycated hemoglobin determinations.

As the clinical utility of glycated hemoglobin (gHb) measurement increases, so does the need for standardization of values between different methods and different laboratories. Using three different methods, we examined the feasibility of interlaboratory standardization of gHb measurement. A liquid-chromatographic (HPLC) system from our research laboratory was designated the reference method. For gHb standards we used erythrocyte hemolysates prepared from blood samples from nondiabetic and diabetic subjects. Values assigned to each standard were based on the mean of multiple gHb determinations by the HPLC method. A clinical laboratory routinely prepared hemolysates and assayed gHb by commercially available ion-exchange ("mini column") and affinity chromatographic methods. For each assay a standard curve was constructed and gHb values were derived from these curves. Samples analyzed in the clinical laboratory were also analyzed in the research laboratory and the curve-derived values were compared with the HPLC-measured values, to determine the accuracy of our interlaboratory standardization procedure. Correlations were excellent (r = 0.99). The lack of significant differences between calculated and HPLC-measured values indicates that interlaboratory standardization is feasible.

Chromatography, Affinity↗
PubMed1985

Measurement of glycosylated whole-blood protein for assessing glucose control in diabetes: collection and storage of capillary blood on filter paper.

We present data on the use of filter-paper blood collection for measurement of glycosylated whole-blood proteins (gWB) (hemoglobin and plasma proteins). A capillary blood sample, obtained by fingerprick, is spotted directly onto filter paper (Schleicher & Schuell 903). The blood spot is washed briefly with alcohol (ethanol or isopropanol) to remove free glucose and dried before shipment to the laboratory. In the laboratory, the blood is eluted from the paper and analyzed for gWB by a colorimetric method. The gWB is primarily a measure of glycosylated hemoglobin (gHb) with a small contribution from glycosylated plasma protein. Concentrations of gWB and gHb are highly correlated (r = 0.91). The filter-paper method offers advantages over currently available methods for quantifying gHb and may be particularly useful in screening for diabetes and for assessing glycemic control in patients from remote areas.

Blood Proteins↗
PubMed1984

Recent advances in glycosylated hemoglobin measurements.

Glycosylated hemoglobins have gained wide acceptance as an accurate index of long-term blood glucose control in diabetes mellitus. A variety of glycosylated hemoglobin assays is available. There is a high degree of correlation between results determined by these assays. The ideal laboratory method for measuring glycosylated hemoglobin in the diabetic should be accurate, precise, easily standardized, inexpensive, and rapidly performed. Unfortunately, none of the currently used methods meet all of the criteria necessary to be considered the ideal laboratory method. The most widely used methods for quantitating glycosylated hemoglobins--including ion exchange chromatography, electrophoresis, isoelectric focusing, thiobarbituric acid colorimetry, and affinity chromatography--are reviewed with respect to the important advantages and disadvantages of each method for the clinical laboratory. Techniques for quantitating glycosylated proteins other than hemoglobins, such as albumin, are also discussed.

Blood Specimen Collection↗
PubMed1983

Glycosylated hemoglobin measured by affinity chromatography: micro-sample collection and room-temperature storage.

Under proper conditions, whole blood can be stored at room temperature for as long as 21 days before measurement of glycosylated hemoglobin by affinity chromatography. Whole blood (anticoagulated with EDTA or heparin) was placed in capillary tubes, which were then sealed at both ends and stored at room temperature. Just before assay, whole blood was rinsed from the tubes and diluted 10-fold with water. Samples of each patient's blood were assayed as whole-blood hemolysates by affinity chromatography after zero, seven, 14, and 21 days of storage. Values for glycosylated hemoglobin did not change over 21 days of storage and values for each storage day correlated well (r = 0.97, p less than .0001) with hemoglobin A1C measured in fresh erythrocyte hemolysates by "high-performance" liquid ion-exchange chromatography.

Blood Specimen Collection↗
PubMed1983

Effects of whole blood storage on results for glycosylated hemoglobin as measured by ion-exchange chromatography, affinity chromatography, and colorimetry.

After storage of whole blood at either 4 or 20 degrees C, results for glycosylated hemoglobin by ion-exchange chromatography ("high-performance" liquid and mini-column chromatography), thiobarbituric acid colorimetry, and affinity chromatography were compared. At 4 degrees C, all methods gave acceptable results for samples stored for as long as a week. At 20 degrees C, the colorimetric and affinity methods also showed sample stability for a week or more. The ion-exchange methods were associated with a marked increase in values for glycosylated hemoglobin after a few days of storage. Evidently, care in details of sample collection and handling is especially important for ion-exchange methods, and the colorimetric and affinity methods have advantages over ion exchange in situations where long delays between sample collection and assay are unavoidable.

Blood Preservation↗
PubMed1982

Glycosylated hemoglobin in Mystromys albicaudatus: a diabetic animal model.

Glycosylated hemoglobin was measured in Mystromys albicaudatus, a rodent model of diabetes mellitus, using a newly developed colorimetric assay. The mean glycosylated hemoglobin for non-diabetic Mystromys (n = 321) was 14.8 nmol hydroxymethylfurfural / 10 mg hemoglobin which is similar to that obtained in non-diabetic humans. Animals with a glycosylated hemoglobin value greater than 19 nmol hydroxymethylfurfural / 10 mg hemoglobin were characterized as diabetics. Significant correlations were found between glycosylated hemoglobin and both plasma glucose and urine glucose levels.

Animals↗
PubMed1982

Determination of glycosylated hemoglobin by affinity chromatography: comparison with colorimetric and ion-exchange methods, and effects of common interferences.

An affinity-chromatographic method for determination of glycosylated hemoglobin (Anal. Lett. 14: 649-661, 1981) is compared with the thiobarbituric acid colorimetric (I) (Clin. Chem. 27: 669-672, 1981) and the ion-exchange liquid-chromatographic (II) (Diabetes 29: 623-628, 1980) methods. A correlation of 0.98 was obtained for the affinity method vs II and 0.97 for affinity vs I (n = 51). The within-run CV was 1.9% for specimens from non-diabetic individuals and 1.0% for those from diabetics. The respective between-run CVs were 3.4% and 2.4%. Failure to remove "labile" glucose adducts by 5-h incubation of erythrocytes in isotonic saline (37 degrees C) contributed an average error of 13.1% for II, 5.4% for I, and 1.6% for the affinity method. Affinity chromatography gave a decrease of 0.1-0.2% glycosylated hemoglobin for each 1.0 degree C temperature increase between 18 and 27 degrees C. Varying the pH of the wash buffer used in the affinity procedure from 7.75 to 8.25 (pH 8.0 optimum) produced at net change of 0.5% in glycosylated hemoglobin with one diabetic specimen. Using the affinity method, we determined the reference interval for glycosylated hemoglobin in 124 apparently healthy individuals to be 5.3 to 7.5% (mean 6.36%, SD 0.55%). Rechromatography by II and isoelectric focusing analysis of the fractions obtained by the affinity separation revealed a substantial population of glycosylated hemoglobins not measured by II. The affinity method offers a rapid, simple, precise, and accurate alternative to methods currently in use and gives substantial freedom from many common interferences.

Adolescent↗