THE DISTRIBUTION OF SUGAR IN NORMAL HUMAN BLOOD

HEMOGLOBIN, GLUCOSE, OXYGEN AND WATER IN THE ERYTHROCYTE: A Concept of Biological Magnitudes, Based upon Molecular Dimensions

Calculations have been presented to illustrate the insight which may be gained from the development of concepts of biological magnitudes upon the basis of molecular dimensions.

Factors affecting blood glucose monitoring: sources of errors in measurement

Glucose monitoring has become an integral part of diabetes care but has some limitations in accuracy. Accuracy may be limited due to strip manufacturing variances, strip storage, and aging. They may also be due to limitations on the environment such as temperature or altitude or to patient factors such as improper coding, incorrect hand washing, altered hematocrit, or naturally occurring interfering substances. Finally, exogenous interfering substances may contribute errors to the system evaluation of blood glucose. In this review, I discuss the measurement of error in blood glucose, the sources of error, and their mechanism and potential solutions to improve accuracy in the hands of the patient. I also discuss the clinical measurement of system accuracy and methods of judging the suitability of clinical trials and finally some methods of overcoming the inaccuracies. I have included comments about additional information or education that could be done today by manufacturers in the appropriate sections. Areas that require additional work are discussed in the final section.

Evidence for interindividual heterogeneity in the glucose gradient across the human red blood cell membrane and its relationship to hemoglobin glycation

OBJECTIVE

To determine whether interindividual heterogeneity in the erythrocyte (red blood cell [RBC]) transmembrane glucose gradient might explain discordances between A1C and glycemic control based on measured fructosamine.

RESEARCH DESIGN AND METHODS

We modeled the relationship between plasma glucose and RBC glucose as the concentration distribution (C(i)-to-C(o) ratio) of a nonmetabolizable glucose analog (14)C-3-O-methyl glucose ((14)C-3OMG) inside (C(i)) and outside (C(o)) RBCs in vitro. We examined the relationship between that distribution and the degree of glycation of hemoglobin in comparison with glycation of serum proteins (fructosamine), the glycation gap. A1C, fructosamine, and in vitro determination of the (14)C-3OMG distribution in glucose-depleted RBCs were measured in 26 fasted subjects.

RESULTS

The C(i)-to-C(o) ratio 0.89 +/- 0.07 for 3-O-methyl-d-glucopyranose (3OMG) ranged widely (0.72-1.04, n = 26). In contrast, urea C(i)-to-C(o) (1.015 +/- 0.022 [range 0.98-1.07], P < 0.0001) did not. Concerning mechanism, in a representative subset of subjects, the C(i)-to-C(o) ratio was retained in RBC ghosts, was not dependent on ATP or external cations, and was reestablished after reversal of the glucose gradient. The 3OMG C(i)-to-C(o) ratio was not correlated with serum fructosamine, suggesting that it was independent of mean plasma glucose. However, C(i)-to-C(o) did correlate with A1C (R(2) = 0.19) and with the glycation gap (R(2) = 0.20), consistent with a model in which differences in internal glucose concentration at a given mean plasma glucose contribute to differences in A1C for given level of glycemic control.

CONCLUSIONS

The data demonstrate interindividual heterogeneity in glucose gradients across RBC membranes that may affect hemoglobin glycation and have implications for diabetes complications risk and risk assessment.

The relationship between 24-hour integrated glucose concentrations and % glycohemoglobin

OBJECTIVE

Since glycohemoglobin values are widely used clinically as a surrogate for average glucose concentration over an extended period of time, we decided to determine the actual relationship between 24-hour integrated glucose values and percent total glycohemoglobin (%tGHb) in cohorts of people with and without diabetes.

RESEARCH DESIGN AND METHODS

In 48 people without known diabetes with known stability of fasting glucose over a 1-year period of time, the calculated 24-hour integrated glucose concentration was compared with their %tGHb. In 15 normal young medical students, the glucose area response was determined from 46 venous blood samples obtained during a 24-hour period and compared with their %tGHb. In 18 people with type 2 diabetes, interstitial glucose concentrations were monitored using the Continuous Glucose Monitoring System (Medtronic MiniMed, Inc., Sylmar, Calif) for 3 days at 20-day intervals over 100 days. %tGHb was performed at 20-day intervals simultaneously. In 29 people with untreated type 2 diabetes, glucose area response was determined from 46 venous blood samples obtained during a 24-hour period and compared with their %tGHb after being on a standardized diet provided to the subjects for at least 5 weeks. The %tGHb and 24-hour profiles were stable.

RESULTS

There was an excellent correlation between the mean 24-hour glucose concentration and the %tGHb among subjects with diabetes. The correlation was poor among subjects without diabetes. The relationship was curvilinear when plotted as a single group. Alternatively when data from subjects with or without diabetes were plotted separately, the slopes were identical but the y-intercepts were different.

CONCLUSION

The relationship between the mean glucose concentration integrated over an extended period of time and the %tGHb is not linear. The reason for this nonlinearity remains to be determined. This non-linearity needs to be considered in the clinical interpretation of %tGHb (and probably HbA(1c)) in reference to glucose values.

Evaluation of a miniaturized thermal biosensor for the determination of glucose in whole blood

A miniaturized thermal biosensor has been evaluated as part of a flow-injection analysis system for the determination of glucose in whole blood. Glucose was determined by measuring the heat evolved when samples containing glucose passed through a small column with immobilized glucose oxidase and catalase. Samples of whole blood (1 microliter) can be measured directly, without any pretreatment. The correlation in the response between the thermal biosensor, the Reflolux S meter (Boehringer Mannheim), the Granutest 100 glucose test kit (Merck Diagnostica) and the Ektachem (Kodak) instrument was evaluated. The influence of the hematocrit value and of possible interferences is reported. The correlation measurements show that the thermal biosensor calibrated with aqueous glucose standards generally gives lower values on blood glucose than the reference methods calibrated for serum or blood measurements. Mean negative biases range from 0.53 to 1.16 mmol/l. Differences in sample treatment clearly complicate comparisons and the proper choice of reference method. There was no influence from substances such as ascorbic acid (0.11 mmol/l), uric acid (0.48 mmol/l), urea (4.3 mmol/l) and acetaminophen (0.17 mmol/l) on the response to 5 mmol/l glucose. The hematocrit value does not influence the glucose determination, for hematocrit values of between 13 and 53%.

Status of platelets in complicated and uncomplicated diabetes mellitus

Thirty patients with diabetes mellitus of more than 5 years' duration, divided into 2 groups of 15 each depending on the presence or absence of vascular complications, constituted the case material for the study. Fifteen healthy subjects of the same age group and sex served as controls.

The platelet count and morphology were normal in controls as well as in patients with diabetes mellitus. The platelet adhesiveness increased signifi cantly with the increase in age and duration of diabetes and in the presence of vascular complications, irrespective of their type. The platelet aggregation time decreased with the increase in age as well as in diabetic patients with vascular complications, but the duration did not have any effect on it. The subject's sex, severity, and adequate control of diabetes mellitus with any type of therapy did not have any influence on the platelet functions studied.