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Laboratory Testing for Diabetes Diagnosis and Management

Laboratory Testing for Diabetes Diagnosis and Management

Test Guide

Laboratory Testing for Diabetes Diagnosis and Management

  

This Test Guide discusses the use of laboratory tests (Table 1) for diagnosing diabetes mellitus and monitoring glycemic control in individuals with diabetes.

Diagnosis

Tools for diagnosing diabetes mellitus include fasting plasma glucose (FPG) measurement, oral glucose tolerance tests (OGTT), and standardized hemoglobin A1c (HbA1c) assays (Table 2). FPG and OGTT tests are sensitive but measure glucose levels only in the short term, require fasting or glucose loading, and give variable results during stress and illness.1 In contrast, HbA1c assays reliably estimate average glucose levels over a longer term (2 to 3 months), do not require fasting or glucose loading, and have less variability during stress and illness.1,2 In addition, HbA1c assays are more specific for identifying individuals at increased risk for diabetes.1 Clinically significant glucose and HbA1c levels are shown in Table 2.1 The American Diabetes Association® (ADA) recommends using these values for diagnosing diabetes and increased diabetes risk (prediabetes).

Management

Following a diagnosis of diabetes, a combination of laboratory and clinical tests can be used to monitor blood glucose control, detect onset and progression of diabetic complications, and predict treatment response. Table 3 shows the recommended testing frequency and target results for these tests. Different laboratory tests are available for monitoring blood glucose control over the short, long, and intermediate term to help evaluate the effectiveness of a management plan.1

Self-monitoring of blood glucose (SMBG) is useful for tracking short-term treatment responses in insulin-treated patients, but its usefulness is less clear in non–insulin-treated patients.1 By contrast, the long-term HbA1c measure should be used as the primary test of glycemic control in all non-pregnant adults with diabetes1; lowering HbA1c levels by 1 percentage point reduces the risk of microvascular complications by approximately 40%.3 To help patients relate long-term glucose control to daily SMBG measurements, HbA1c test results may be converted to conventional glucose units (mg/dL or mmol/L) and reported as the estimated average glucose (eAG).1,2,4,5

Fructosamine testing is an alternative to HbA1c testing for monitoring glycemic control over the intermediate term (1 to 2 weeks) and is particularly useful when there are discrepancies between HbA1c and SMBG.6

Despite their value, neither HbA1c, nor fructosamine testing, specifically measures postprandial plasma glucose (PPG) excursions. These excursions contribute more to hyperglycemia in individuals with moderately or well-controlled HbA1c levels (6.5% to 8.0%) than in those with higher HbA1c levels7; PPG elevations also independently increase the risk of cardiovascular death.8 PPG excursions over the short- to intermediate-term (3 days to 2 weeks) can be evaluated with the GlycoMark® test.6,9,10 Available data support the use of this assay as a complement to HbA1c testing in patients with moderately or well-controlled HbA1c levels (Figure).6,9-13

Figure. Suggested Use of the GlycoMark® Test

Individuals with diabetes are at increased risk of heart and kidney disease, retinopathy, neuropathy, and nonalcoholic fatty liver disease (NAFLD). Routine eye and foot exams, along with blood pressure, lipids, microalbumin, creatinine/eGFR, and liver function testing are recommended to detect the onset and monitor progression of these complications.1

Tables 1, 2, and 3 are provided for informational purposes only and are not intended as medical advice. A physician's test selection and interpretation, diagnosis, and patient management decisions should be based on his/her education, clinical expertise, and assessment of the patient.

Table 1. Tests Used in Diabetes Diagnosis and Management

Test Code

Test Name

Primary Clinical Use and Differentiating Factors

Diagnosing Diabetes and Monitoring Blood Glucose Control

92027

Diabetes Risk Panel with Scorec

Includes glucose (483X); HbA1c (496); total (334), HDL (608), and LDL (calculated) cholesterol; triglycerides (896) with reflex to direct LDL (8293); cholesterol/HDL ratio (calculated); non-HDL (calculated); and 8-year risk of developing diabetes (calculated).

Diagnosis of prediabetes

Assesses risk for developing type 2 diabetes mellitus

Identifies patients suitable for lifestyle interventions and/or pharmacotherapy

91920

Diabetes Risk Panel without Scorec

Includes glucose (483X); HbA1c (496); total (334), HDL (608), and LDL (calculated) cholesterol; triglycerides (896) with reflex to direct LDL (8293); cholesterol/HDL ratio (calculated); and non-HDL (calculated).

Diagnosis of prediabetes

Assesses risk for developing type 2 diabetes mellitus

Identifies patients suitable for lifestyle interventions and/or pharmacotherapy

91712(X)

Diabetes, Newly Diagnosed and Monitoring Panelc

Includes glucose (483X); HbA1c (496); hepatic function panel (total protein [754], albumin [223], globulin [calculated], albumin/globulin ratio [calculated], total [287], direct [285], and indirect [calculated] bilirubin, alkaline phosphatase [234], AST [822], and ALT [823]); lipid panel (total [334], HDL [608], and LDL [calculated] cholesterol; triglycerides [896] with reflex to direct LDL [8293]; cholesterol/HDL ratio [calculated]; and non-HDL [calculated]); serum creatinine [375X]; and urinary microalbumin with creatinine (6517).

Management; establishes baseline measurements for patients recently diagnosed with diabetes mellitus

Monitors patients with diabetes mellitus

8340

Fructosamine

Management; measures glycemic control over the intermediate term (1 to 2 weeks)

484

Glucose, Plasma

Diagnosis based on FPG

35181

Glucose Tolerance Test, 2 Specimens (75g)

Diagnosis based on fasting and 2-hour (post 75g glucose loading) specimens (2-h OGTT)

6745

Glucose Tolerance Test, Gestational, 4 Specimens (100g)

Diagnosis of gestational diabetes

19599

GlycoMark®

Management; measures PPG excursions; may help differentiate contributions of FPG and PPG to hyperglycemia in patients with moderately or well-controlled HbA1c levels. See Figure.

496

Hemoglobin A1ca

Diagnosis and management; determines long-term average blood glucose, expressed as a percentage.

16802

Hemoglobin A1c with eAGa

Management; determines long-term average blood glucose; expressed in percent HbA1c and calculated estimated average glucose (eAG) in conventional blood glucose units for more convenient comparison to SMBG values.1,2,4,5

16320

Hemoglobin A1c with eAG with Reflex to GlycoMark®a,b

Management; determines long-term average blood glucose levels, expressed in percent HbA1c and calculated estimated average glucose (eAG).

Measures PPG excursions; may help differentiate contributions of FPG and PPG to hyperglycemia in patients with moderately or well-controlled HbA1c levels.

16715

Hemoglobin A1c with Reflex to GlycoMark®a,b

Management; determines long-term average blood glucose levels, expressed as a percentage.

Measures PPG excursions; may help differentiate contributions of FPG and PPG to hyperglycemia in patients with moderately or well-controlled HbA1c levels.

NA

Self-Monitoring of Blood Glucose (SMBG)

Management; determines response to insulin therapy on a daily basis.

Monitoring Diabetic Complications

Laboratory Tests

375(X)

Creatinine

Includes estimated glomerular filtration rate (eGFR)

Management; monitors onset and progression of kidney disease

91713(X)

Diabetes, Advancing Chronic Kidney Disease Management Panelc

Includes electrolyte panel (sodium [836], potassium [733], chloride [330], carbon dioxide [310]), hemoglobin (510X), intact PTH and calcium (8837), phosphate (phosphorus [718]), total 25-hydroxyvitamin D by immunoassay (17306), serum creatinine [375X]; and urinary microalbumin with creatinine (6517).

Management; monitors chronic kidney disease in patients with diabetic nephropathy

92062

Diabetes and ASCVD Risk Panel with Scoresc

Includes glucose (483X); HbA1c (496); total (334), HDL (608), and LDL (calculated) cholesterol; triglycerides (896) with reflex to direct LDL (8293); cholesterol/HDL ratio (calculated); non-HDL (calculated); 8-year risk of developing diabetes (calculated); and 10-year and lifetime atherosclerotic cardiovascular risk scores (calculated).

Diagnosis of prediabetes
Assesses risk for developing type 2 diabetes mellitus and cardiovascular disease
Identifies patients suitable for lifestyle interventions and/or pharmacotherapy

7600

Lipid Panelc

Includes total (334), HDL (608), and LDL (calculated) cholesterol; triglycerides (896); cholesterol/HDL ratio (calculated); non-HDL (calculated)

Management; monitors dyslipidemia and thus risk of heart disease

6517

Microalbumin, Random Urine with Creatinine

Management; monitors onset and progression of kidney disease

91979

NAFLD Fibrosis Scorec

Includes albumin (223), AST (822), ALT (823), glucose (483X); platelet count (723), and AST/ALT ratio (calculated)

Management; monitors onset and progression of NAFLD

Clinical Tests

NA

Blood pressure

Management; monitors hypertension and thus risk of heart disease

NA

Eye exam

Management; monitors onset and progression of eye disease

NA

Foot exam

Management; monitors onset and progression of nerve disease and peripheral arterial disease

ALT, alanine aminotransferase; ASCVD, atherosclerotic cardiovascular disease; AST, aspartate aminotransferase; eAG, estimated average glucose; FPG, fasting plasma glucose; HbA1c, hemoglobin A1c; NA, not available through Quest Diagnostics; NAFLD, nonalcoholic fatty liver disease; OGTT, oral glucose tolerance test; PPG, postprandial plasma glucose; PTH, parathyroid hormone.

a

Determined using a National Glycohemoglobin Standardization Program (NGSP)-certified HbA1c method that is corrected for common hemoglobin variants.14

b

Reflex tests are performed at additional charge and are associated with an additional CPT code.

c

Panel components may be ordered separately.

Table 2. Diagnostic Significance of Glucose and Hemoglobin A1c Concentrations1

Individuals Suitable for Testing

Marker

Clinically Significant Level

Interpretation

Non-pregnant individuals with diabetes risk factors or age ≥45 years and pregnant women with risk factors (first prenatal visit)

FPG

≥126 mg/dL

Diabetes mellitusa,b,c

2-h OGTT (75 g)

≥200 mg/dL

HbA1c leveld

≥6.5%

FPG

100 to125 mg/dL

Increased risk for diabetesb

2-h OGTT (75 g)

140 to199 mg/dL

HbA1c leveld

5.7% to 6.4%

All pregnant women (24-28 weeks of gestation)

2-h OGTT (75 g)

Gestational diabetese

• Fasting

• 1 h

• 2 h

≥92 mg/dL

≥180 mg/dL

≥153 mg/dL

FPG, fasting plasma glucose; OGTT, oral glucose tolerance test; HbA1c, hemoglobin A1c.

a

Unless unequivocal hyperglycemia is present, diagnosis requires 2 clinically significant test results (either the same test using a new blood sample or 2 different tests). If 2 different tests (eg, HbA1c and FPG) are performed and 1 gives clinically significant results and the other does not, the test with clinically significant results should be repeated. If the repeat test result is also clinically significant, diabetes is diagnosed.1

b

If tests are normal, repeat testing at 3-year intervals.1

c

If tests are close to diagnostic thresholds, repeat testing in 3 to 6 months.

d

HbA1c testing is contraindicated in patients with abnormal red cell turnover.1,14

e

Only 1 of the 3 time points needs to be elevated to make the diagnosis.1

Table 3. Recommended Testing Frequency and Goals for Diabetes Management1

Marker

Target Levels in Patients with Diabetesa

Testing Frequencyb

Blood Glucose

SMBG

Patients using multiple insulin injections or an insulin pump:
80 to 130 mg/dL (fasting or before meals)
<180 mg/dL (1 to 2 hours after start of meal)
≤95 mg/dL (gestational diabetes; fasting or before meals)
≤140 mg/dL (gestational diabetes; 1 hour postmeal)
≤120 mg/dL (gestational diabetes; 2 hours postmeal)

Varies for individuals but usually 6 to ≥10 times daily including:

  • Prior to meals and snacks and occasionally after meals
  • When they suspect low blood glucose or after treating low blood glucose until levels are normal
  • Prior to exercise or driving
  • Bedtime

HbA1c Test

HbA1c level

Nonpregnant adults: <7.0%

Patients who are recently diagnosed, otherwise healthy, or not at significant risk for hypoglycemia: <6.5%

Patients with a history of severe hypoglycemia, extensive comorbidities, or a long-standing diagnosis in whom lower targets are difficult to achieve: <8%

  • Initial visit
  • Follow-up: 
  •    Every 6 months for patients with stable glycemia who meet glycemic goals

       Every 3 months for patients who have changed therapy or are not meeting glycemic goals

       More frequently for patients with unstable glycemia and those undergoing intensive management (eg, pregnant women with type 1 diabetes)

eAGc

<154 mg/dL (8.6 mmol/L)

Same as for HbA1c level

GlycoMark® Test

1,5-AG level

≥8.0 µg/mL

At time of HbA1c test if HbA1c levels are moderately or well-controlled to detect PPG excursions.
As clinically indicated to monitor short- to intermediate-term glucose control.

Monitoring Diabetic Complications

Laboratory Tests

Creatinine level and eGFR

eGFR ≥60 mL/min/1.73 m2

Every year

Fasting lipid profile (LDL, HDL, triglycerides)

LDL: <100 mg/dL

Initial visit and every 5 years thereafter (adults not taking statins); as needed to monitor adherence and efficacy of introducing statin therapy or for patients with CVD

Urine albumin/microalbumin levels

<30 µg/mg creatinine is normal

Once a year in patients with type 1 diabetes who have had diabetes for at least 5 years; once a year in all patients with type 2 diabetes

Clinical Tests

Blood pressure

Most patients:
<140/90 mmHg
High risk of CVD:
≤130/80 mmHg

Pregnant:
≤120 to 160/80 to 105 mmHg

At every routine visit

Eye exam

Normal

Initial exam within 5 years of onset (type 1) or shortly after diagnosis (type 2). Every year or every 2 years following normal screening; more frequently if progressive eye disease

Full foot exam

Normal

Every year

ADA, American Diabetes Association; 1,5-AG, 1,5-anhydroglucitol; eAG, estimated average glucose; HbA1c, hemoglobin A1c; SMBG, self-monitoring of blood glucose.

a

Achieving glucose, HbA1c, eAG, and 1,5-AG goals should be balanced against risk of inducing hypoglycemia.

b

Suggested testing frequency is generalized for routine monitoring and may vary depending on clinical condition and treatment regimen.1,12,13

c

eAG values in mg/dL are calculated by converting HbA1c levels to eAG using the following formula: eAG = HbA1c x 28.7 - 46.7.4,5 eAG values in mg/dL can be converted to mmol/L by dividing by 18.

References

  1. American Diabetes Association. Standards of medical care in diabetes—2017. Diabetes Care. 2017;40(suppl 1):S1-S120.

  2. American Diabetes Association. A1C and eAG. http://www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/a1c/. Updated September 29, 2014. Accessed February 7, 2017.

  3. Stratton IM, Adler AI, Neil HA, et al. Association of glycaemia with macrovascular and microvascular complications of type 2 diabetes (UKPDS 35): prospective observational study. BMJ. 2000;321:405-412.

  4. Nathan DM, Kuenen J, Borg R, et al. Translating the A1C assay into estimated average glucose values. Diabetes Care. 2008;31:1473-1478.

  5. American Diabetes Association. eAG/A1C conversion calculator. http://professional.diabetes.org/diapro/glucose_calc. Accessed February 7, 2017.

  6. Dungan KM. 1,5-Anhydroglucitol (GlycoMark) as a marker of short-term glycemic control and glycemic excursions. Expert Rev Mol Diagn. 2008;8:9-19.

  7. Monnier L, Lapinski H, Colette C. Contributions of fasting and postprandial plasma glucose increments to the overall diurnal hyperglycemia of type 2 diabetic patients: variations with increasing levels of HbA(1c). Diabetes Care. 2003;26:881-885.

  8. DECODE Study Group. European Diabetes Epidemiology Group. Is the current definition for diabetes relevant to mortality risk from all causes and cardiovascular and noncardiovascular diseases? Diabetes Care. 2003;26:688-696.

  9. Dungan KM, Buse JB, Largay J, et al. 1,5-Anhydroglucitol and postprandial hyperglycemia as measured by continuous glucose monitoring system in moderately controlled patients with diabetes. Diabetes Care. 2006;29:1214-1219.

  10. GlycoMark [package insert]. GlycoMark, Inc., New York, NY October 2013.

  11. Kim WJ, Park CY. 1,5-Anhydroglucitol in diabetes mellitus. Endocrine. 2013;43:33-40.

  12. McGill JB, Cole TG, Nowatzke W, et al. Circulating 1,5-anhydroglucitol levels in adult patients with diabetes reflect longitudinal changes of glycemia: a U.S. trial of the GlycoMark assay. Diabetes Care. 2004;27:1859-1865.

  13. Yamanouchi T, Ogata N, Tagaya T, et al. Clinical usefulness of serum 1,5-anhydroglucitol in monitoring glycaemic control. Lancet. 1996;347:1514-1518.

  14. National Glycohemoglobin Standardization Program. Factors that interfere with HbA1c test results. http://www.ngsp.org/factors.asp. Updated December 29, 2016. Accessed February 7, 2017.
     

Content reviewed 06/2017

 
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* The tests listed by specialist are a select group of tests offered. For a complete list of Quest Diagnostics tests, please refer to our Directory of Services.