Lab analysis in diabetes — a preview of what’s to come

Amy Carpenter Aquino

November 2021—The guidelines for laboratory analysis in the diagnosis and management of diabetes mellitus are being revised and will be released next year. In a virtual session at the AACC meeting in September, laboratorians got a look at some of the recommendations to come.

“Long before there was a COVID pandemic there was a diabetes pandemic,” said David B. Sacks, MB ChB, chair of the expert committee leading the revision and senior investigator and chief of the clinical chemistry service, NIH Clinical Center. He and a co-presenter—professor Åke Lernmark of Lund University—presented preliminary recommendations related to glycolysis, glycated protein, gestational diabetes mellitus, lab analysis in the diagnosis of type 1 diabetes onset, and genetic risk markers.

“We are at the stage where the recommendations are being graded, so we’re fairly close to the completion of the initial draft of the document,” said Dr. Sacks, who noted they intend to publish the guidelines in both Clinical Chemistry and Diabetes Care. The last set of such guidelines was published a decade ago (Sacks DB, et al. Clin Chem. 2011;57[6]:e1–e47; Sacks DB, et al. Diabetes Care. 2011;34[6]:e61–99).

The aim of the first recommendation Dr. Sacks highlighted is to minimize glycolysis, and it says a tube containing a rapidly effective glycolytic inhibitor, such as granulated citrate buffer, should be used. If this cannot be achieved, it says, the sample tube should immediately be placed in an ice-water slurry and subjected to centrifugation to remove the cells within 15 to 30 minutes. Tubes with only enolase inhibitors, such as sodium fluoride, should not be relied on to prevent glycolysis.

A new study “demonstrates very nicely the glycolysis in different tubes,” Dr. Sacks said (Fischer MM, et al. Clin Chem. 2021;67[7]:1032–1034). In comparing the effects of glycolysis inhibitors, Fischer, et al., evaluated blood collected in six tubes: Three tubes contained either lithium heparin, EDTA, or sodium fluoride, and three other tubes contained citrate and were from different manufacturers. (Citrate-containing tubes, Dr. Sacks noted, are not available in the U.S. but are used in other countries, particularly in Europe.) The samples stood at room temperature and were centrifuged at various time points up to 24 hours.

The difference to the lithium heparinized tube at times zero was taken as the standard, and the findings revealed a statistically significant decrease in the lithium heparin and EDTA tubes at 30 minutes, Dr. Sacks said, with the decreases continuing uninterrupted. The sodium fluoride tube showed a statistically significant decrease at 15 minutes, but the rate of decline leveled off.

Among the three citrate tubes, the decreases became statistically significant at 15 minutes, four hours, or 24 hours, depending on the manufacturer, he said. “Even though it was statistically significant, the decrease was very, very small and unlikely to be clinically significant.”

Another new recommendation says all pregnant women with risk factors for diabetes should be tested for undiagnosed prediabetes and diabetes at the first prenatal visit using standard diagnostic criteria.

“Gestational diabetes mellitus has been defined for many years as glucose intolerance first recognized during pregnancy,” he said. “This has changed more recently.”

The rationale for the recommendation, Dr. Sacks said, is it’s estimated globally about five percent of women ages 18 to 44 have diabetes, and about 50 percent of these women have not been diagnosed. About 24 percent of women of the same ages have prediabetes, Dr. Sacks said, and 90 percent of those women are undiagnosed. “If you combine those numbers, close to one third of women of reproductive age have impaired glucose metabolism, and the overwhelming majority are not aware they have this,” he said.

The following standard recommendation continues: All pregnant women not previously known to have diabetes should be evaluated for GDM at 24 to 28 weeks of gestation.

A related new recommendation says women with GDM should be tested for diabetes four to 12 weeks postpartum using nonpregnant OGTT criteria exclusively. And another says lifelong screening for diabetes should be performed in women with a history of GDM using standard nonpregnant criteria at least every three years.

“The rationale is that women with GDM are at increased risk for type 2 diabetes, and recent estimates range from seven- to 12-fold,” Dr. Sacks said. “And importantly, the cumulative evidence of type 2 diabetes after GDM is 50 to 60 percent, so it’s important to monitor these people.”

In the upcoming revision will be two new recommendations for glycated protein. One says in clinical settings where interfering factors compromise interpretation of HbA1c results, assays of other glycated proteins, such as fructosamine or glycated albumin, may be used. Another says HbA1c values that are inconsistent with the clinical presentation should be investigated further, and that a comparison of suspicious HbA1c results with other glycated protein assays may be informative.

“The rationale,” Dr. Sacks said, “is that any factor that significantly alters red blood cell lifespan will alter hemoglobin A1c. So if the red cell lifespan is shortened, there will be less time for glucose to attach to hemoglobin to form glycated hemoglobin or hemoglobin A1c, so the hemoglobin and A1c will be lower than expected from the patient’s average glucose.”

Fructosamine and glycated albumin reflect glycation of serum proteins, he said, “and because of this, the value is independent of red blood cells.”

“It should be noted that the half-life of albumin in the blood is considerably shorter than that of red blood cells, so they represent the average glycemia over 14 to 21 days rather than the couple of months represented by hemoglobin A1c.”

Far less evidence is available for these glycated serum proteins than there is for hemoglobin A1c, Dr. Sacks said.

The time trends in incidence rate of type 1 diabetes in children worldwide is increasing in most locations, except Japan and Mexico, said expert committee member Dr. Lernmark of Lund and Skane University Hospital in Sweden. “In all other countries listed, there is a steady increase of the disease.” The past decade has also seen significant advances in the research of biomarkers to predict type 1 diabetes in children.