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Inaccurate Hemoglobin A1C Levels in Patients with Type 1 Diabetes and Hereditary Persistence of Hemoglobin F
Inaccurate Hemoglobin A1C Levels in Patients with Type 1 Diabetes and Hereditary Persistence of Hemoglobin F ERIC I. FELNER, MD,
AND
MAUREEN MCGRATH, APRN-BC
We report 2 African-American boys with type 1 diabetes and hereditary persistence of hemoglobin F. The diagnosis came to light after both patients exhibited inconsistent hemoglobin A1C (HbA1C) levels with respect to serum glucose measurements. This demonstrates the importance of frequent glucose monitoring and interpreting the HbA1C level in light of serum glucose measurements. (J Pediatr 2008;153:137-9)
onitoring of hemoglobin A1C (HbA1C), an irreversible nonenzymatic glycation at 1 or both NH2-terminal valines of the  chain of the hemoglobin (Hb) molecule,1 is used to evaluate plasma glucose concentration over prolonged periods. Formation of HbA1C occurs over the average life span of erythrocytes, with the amount of HbA1C depending on the average glucose concentration over the previous 8 to 12 weeks.2 In persons with diabetes, HbA1C concentration provides an indication of the effectiveness of therapy, as well as the risk of developing long-term sequelae of hyperglycemia. The American Diabetes Association recommends an HbA1C goal of ⬍ 7% for adults and ⬍ 8% for children with diabetes; for nondiabetics, an HbA1C ⬍ 6% is normal.3,4 We describe 2 patients who were found to have hereditary persistence of hemoglobin F (HPHF) when their HbA1C values did not correlate with self-monitored blood glucose (SMBG) levels.
M
REPORTS OF CASES Case 1 An 8-year, 1-month– old African-American boy was diagnosed with T1D and started on subcutaneous insulin therapy. Over the next 18 months, his HbA1C remained in the normal range, but mean SMBG measurements suggested frequent hyperglycemia (Table I). The patient denied polyuria, polydypsia, or nocturia, and his growth and development were appropriate. According to glucometer readings, he was monitoring his glucose value only an average of twice daily. At each visit, he was reminded of the importance of more frequent monitoring. Due to his infrequent SMBG testing and normal HbA1C values, no significant adjustments were made in his insulin dose. Two years after diagnosis, he presented with evidence of hyperglycemia (polyuria, polydypsia, and nocturia), significant weight loss, and an HbA1C value (6.3%) that deviated significantly from his mean SMBG concentration (346 mg/dL). His fructosamine concentration (464 mol/L; normal, ⬍ 285 mol/L) was consistent with his mean SMBG concentration, and Hb electrophoresis confirmed HPHF (Table II). Revisions were made in the patient’s insulin regimen, and he was again encouraged to perform more frequent self-monitoring.
See editorial, p 7
Case 2 An 8-year, 3-month– old African-American boy was diagnosed with T1D and started on a regimen of subcutaneous insulin injections. Similar to Case 1, his HbA1C remained in the normal range despite elevated SMBG concentrations during the first 18 months after diagnosis (Table I). Due to the lack of clinical evidence of hyperglycemia or growth delay, as well as the patient’s infrequent SMBG testing (an average of twice daily), no significant adjustments were made in his insulin dose. Two years after diagnosis, the Hb HbA1C HbAC HbAS HPHF
Hemoglobin Hemoglobin A1C Hemoglobin C trait Hemoglobin S trait Hereditary persistence of hemoglobin F
HPLC HS SMBG T1D
High-performance liquid chromatography Hereditary spherocytosis Self-monitored blood glucose Type 1 diabetes
From the Department of Pediatrics, Division of Endocrinology, Emory University School of Medicine, Atlanta, GA. Submitted for publication Oct 5, 2007; last revision received Dec 27, 2007; accepted Jan 18, 2008. Reprint requests: Eric I. Felner, MD, Emory University School of Medicine, Department of Pediatrics, Division of Endocrinology, 2015 Uppergate Drive, Atlanta, GA 30322. E-mail: [email protected]. 0022-3476/$ - see front matter Copyright © 2008 Mosby Inc. All rights reserved. 10.1016/j.jpeds.2008.01.024
137
Table 1. HbA1C levels* and mean SBGM levels in 2 patients with HPHF and T1D Case 1 Case 2 Time (months Mean Mean after glucose glucose diagnosis) HbA1C (%) (mg/dL) HbA1C (%) (mg/dL) Diagnosis (0) ⫹4 ⫹8 ⫹12 ⫹16 ⫹20 ⫹24
9.2 4.5 6.3 6.0 6.1 6.5 6.3
— 150 284 298 269 363 346
8.5 6.9 4.8 5.6 4.9 5.9 6.5
— 170 110 158 152 155 238
*All HbA1C tests were performed on a DCA 2000 (Bayer HealthCare) using an immunoassay method.
Table II. Hemoglobin electrophoresis in 2 patients with HPHF and T1D Hemoglobin
Case 1
Case 2
Normal range
Hb (g/dL) HbA1 (%) HbA2 (%) HBF (%)
13.8 64.5 1.9 33.6
14.3 71.0 2.0 27.0
11.5 to 15.5 97.0 to 98.0 1.5 to 2.5 0.5 to 1.0
patient presented with hyperglycemia, significant weight loss, and an HbA1C value (6.5%) that differed significantly from his mean SMBG measurement (238 mg/dL). His fructosamine concentration (390 mol/L) was consistent with his mean SMBG concentration, and Hb electrophoresis confirmed HPHF (Table II). Revisions were made in his insulin regimen, and he too was encouraged to perform more frequent self-glucose testing.
DISCUSSION Disorders that result in a structurally abnormal Hb or insufficient Hb production can affect the accuracy of HbA1Cmeasurements. These effects may vary depending on the specific Hb variant and method used to measure HbA1C.5 More than 700 Hb variants are known, most of which are clinically silent. Most silent variants arise from point mutations in the Hb chains, with HbS trait (HbAS) and HbC trait (HbAC) the most common.6 For most testing methods, HbA1C is accurate in diabetics with HbAS or HbAC.6 In diabetics with clinically significant hemoglobinopathies, HbA1C does not accurately reflect glycemic control regardless of the testing method used.6 The most common clinically significant hemoglobinopathies include sickle cell disease, thalassemia, and hereditary spherocytosis (HS). In those with sickle cell disease (ie, HbSS, HbSC, HbCC) or HS, HbA1C is unreliable because the red cell life is reduced, thereby preventing glycosylation before HbA1C is removed from serum. In those with thalassemia or another Hb variant, 138
Felner and McGrath
red cell life is normal, but the amount of HbA1C is reduced.6 In African-Americans, the most common clinically significant hemoglobinopathy is HbSS, with a prevalence of 0.2 %.7 HPHF is an inherited disorder in which HbF persists throughout life.8 At birth, HbF accounts for up to 90% of the circulating Hb. Its synthesis declines during the third trimester, and it is gradually replaced by HbA over the first year of life. Few individuals with HPHF are identified with HbF, because they are asymptomatic. In HPHF, HbF accounts for ⬎ 20% of total Hb. Individuals with certain congenital or acquired disorders also may have elevated HbF levels, but still accounting for only 10% to 15% of total Hb. After the first year of life, the normal HbF value is ⬍ 1% of total Hb.9 In African-Americans, HPHF has a prevalence of only 0.02%.8,9 These 2 cases demonstrate how HPHF can interfere with the accurate measurement of HbA1C. In the immunoassay that we use (DCA 2000; Bayer HealthCare, Leverkusen, Germany), HbA1C is expressed as a percentage of total Hb, and the antibodies do not recognize non-HbA species.10 In those with Hb variants and normal Hb levels, the greater the percentage of non-HbA, the lower the HbA1C.10 This is the likely explanation as to why Case 1, who had more HbF (and less HbA), exhibited greater inconsistencies between HbA1C and mean SMBG level compared with Case 2. Both boys also had abnormal HbA1C levels at diagnosis but normal levels after initiation of insulin therapy; this is likely due to the significantly higher glucose levels before insulin therapy and also possibly to a mild variation of HbF and HbA over time. Many methods for evaluating HbA1C are available. For diabetics with Hb variants, published data are available regarding the accuracy of HbA1C testing methods.6 For diabetics with hemoglobinopathies, high-performance liquid chromatography (HPLC) is the most accurate technique for measuring HbA1C.10 Using HPLC, HbA1C percentages can be corrected by recalculating them as a percentage of total HbA; however, these corrections are not possible with the immunoassay method.10 The fructosamine test is another method used to assess glycemic control in diabetics with hemoglobinopathies; however, it provides glycemic assessment only over a short time frame (2 weeks), and its value in predicting long-term diabetic complications has not yet been evaluated.6 Diabetics with hemoglobinopathies should be monitored using an HbA1C testing method that yields reliable results. For all patients with diabetes, glycemic control should be assessed with frequent SMBG testing and the results correlated with HbA1C value.
REFERENCES 1. Eckfield JH, Bruns DE. Another step toward standardization of methods for measuring hemoglobin A1C [editorial]. Clin Chem 1997;43:1944-51. 2. John WG. Glycated haemoglobin analysis. Ann Clin Biochem 1997;34:17-31. 3. American Diabetes Association. Standards of medical care in diabetes. Diabetes Care 2007;30(Suppl 1):S4-41. 4. American Diabetes Association. Care of children and adolescents with type 1 diabetes. Diabetes Care 2005;28:186-212. 5. Weykamp CW, Penders TJ, Siebelder CW, Muskiet FA, van der Slik W. Interference of carbamylated and acetylated hemoglobins in assays of glycohemoglobin
The Journal of Pediatrics • July 2008
by HPLC, electrophoresis, affinity chromatography, and enzyme immunoassay. Clin Chem 1993;39:138-42. 6. Bry L, Chen PC, Sacks DB. Effects of hemoglobin variants and chemically modified derivatives on assays for glycohemoglobin. Clin Chem 2001;47: 153-63. 7. Ashley-Kock A, Yang Q, Olney RS. Sickle hemoglobin (Hb S) allele and sickle cell disease. Am J Genet 2000;151:839-45.
8. Hoyer JD, Penz CS, Fairbanks VF, Hanson CA, Katzmann JA. Flow cytometric measurement of hemoglobin F in RBCs. Am J Clin Pathol 2002;117:857-63. 9. Henney MM, Delgrosso K, Robinson R, Johnson CA, Daeschner CW, Campbell TA, et al. Interpretation of fetal hemoglobin only on newborn screening for hemoglobin. J Pediatr Hematol Oncol 2002;24:499-502. 10. Puukka R, Puukka M. Effect of hemoglobin F on measurements of hemoglobin A1C with physicians’ office analyzers. Clin Chem 1994;40:342-3.
Inaccurate Hemoglobin A1C Levels in Patients with Type 1 Diabetes and Hereditary Persistence of Hemoglobin F
139
AND
MAUREEN MCGRATH, APRN-BC
We report 2 African-American boys with type 1 diabetes and hereditary persistence of hemoglobin F. The diagnosis came to light after both patients exhibited inconsistent hemoglobin A1C (HbA1C) levels with respect to serum glucose measurements. This demonstrates the importance of frequent glucose monitoring and interpreting the HbA1C level in light of serum glucose measurements. (J Pediatr 2008;153:137-9)
onitoring of hemoglobin A1C (HbA1C), an irreversible nonenzymatic glycation at 1 or both NH2-terminal valines of the  chain of the hemoglobin (Hb) molecule,1 is used to evaluate plasma glucose concentration over prolonged periods. Formation of HbA1C occurs over the average life span of erythrocytes, with the amount of HbA1C depending on the average glucose concentration over the previous 8 to 12 weeks.2 In persons with diabetes, HbA1C concentration provides an indication of the effectiveness of therapy, as well as the risk of developing long-term sequelae of hyperglycemia. The American Diabetes Association recommends an HbA1C goal of ⬍ 7% for adults and ⬍ 8% for children with diabetes; for nondiabetics, an HbA1C ⬍ 6% is normal.3,4 We describe 2 patients who were found to have hereditary persistence of hemoglobin F (HPHF) when their HbA1C values did not correlate with self-monitored blood glucose (SMBG) levels.
M
REPORTS OF CASES Case 1 An 8-year, 1-month– old African-American boy was diagnosed with T1D and started on subcutaneous insulin therapy. Over the next 18 months, his HbA1C remained in the normal range, but mean SMBG measurements suggested frequent hyperglycemia (Table I). The patient denied polyuria, polydypsia, or nocturia, and his growth and development were appropriate. According to glucometer readings, he was monitoring his glucose value only an average of twice daily. At each visit, he was reminded of the importance of more frequent monitoring. Due to his infrequent SMBG testing and normal HbA1C values, no significant adjustments were made in his insulin dose. Two years after diagnosis, he presented with evidence of hyperglycemia (polyuria, polydypsia, and nocturia), significant weight loss, and an HbA1C value (6.3%) that deviated significantly from his mean SMBG concentration (346 mg/dL). His fructosamine concentration (464 mol/L; normal, ⬍ 285 mol/L) was consistent with his mean SMBG concentration, and Hb electrophoresis confirmed HPHF (Table II). Revisions were made in the patient’s insulin regimen, and he was again encouraged to perform more frequent self-monitoring.
See editorial, p 7
Case 2 An 8-year, 3-month– old African-American boy was diagnosed with T1D and started on a regimen of subcutaneous insulin injections. Similar to Case 1, his HbA1C remained in the normal range despite elevated SMBG concentrations during the first 18 months after diagnosis (Table I). Due to the lack of clinical evidence of hyperglycemia or growth delay, as well as the patient’s infrequent SMBG testing (an average of twice daily), no significant adjustments were made in his insulin dose. Two years after diagnosis, the Hb HbA1C HbAC HbAS HPHF
Hemoglobin Hemoglobin A1C Hemoglobin C trait Hemoglobin S trait Hereditary persistence of hemoglobin F
HPLC HS SMBG T1D
High-performance liquid chromatography Hereditary spherocytosis Self-monitored blood glucose Type 1 diabetes
From the Department of Pediatrics, Division of Endocrinology, Emory University School of Medicine, Atlanta, GA. Submitted for publication Oct 5, 2007; last revision received Dec 27, 2007; accepted Jan 18, 2008. Reprint requests: Eric I. Felner, MD, Emory University School of Medicine, Department of Pediatrics, Division of Endocrinology, 2015 Uppergate Drive, Atlanta, GA 30322. E-mail: [email protected]. 0022-3476/$ - see front matter Copyright © 2008 Mosby Inc. All rights reserved. 10.1016/j.jpeds.2008.01.024
137
Table 1. HbA1C levels* and mean SBGM levels in 2 patients with HPHF and T1D Case 1 Case 2 Time (months Mean Mean after glucose glucose diagnosis) HbA1C (%) (mg/dL) HbA1C (%) (mg/dL) Diagnosis (0) ⫹4 ⫹8 ⫹12 ⫹16 ⫹20 ⫹24
9.2 4.5 6.3 6.0 6.1 6.5 6.3
— 150 284 298 269 363 346
8.5 6.9 4.8 5.6 4.9 5.9 6.5
— 170 110 158 152 155 238
*All HbA1C tests were performed on a DCA 2000 (Bayer HealthCare) using an immunoassay method.
Table II. Hemoglobin electrophoresis in 2 patients with HPHF and T1D Hemoglobin
Case 1
Case 2
Normal range
Hb (g/dL) HbA1 (%) HbA2 (%) HBF (%)
13.8 64.5 1.9 33.6
14.3 71.0 2.0 27.0
11.5 to 15.5 97.0 to 98.0 1.5 to 2.5 0.5 to 1.0
patient presented with hyperglycemia, significant weight loss, and an HbA1C value (6.5%) that differed significantly from his mean SMBG measurement (238 mg/dL). His fructosamine concentration (390 mol/L) was consistent with his mean SMBG concentration, and Hb electrophoresis confirmed HPHF (Table II). Revisions were made in his insulin regimen, and he too was encouraged to perform more frequent self-glucose testing.
DISCUSSION Disorders that result in a structurally abnormal Hb or insufficient Hb production can affect the accuracy of HbA1Cmeasurements. These effects may vary depending on the specific Hb variant and method used to measure HbA1C.5 More than 700 Hb variants are known, most of which are clinically silent. Most silent variants arise from point mutations in the Hb chains, with HbS trait (HbAS) and HbC trait (HbAC) the most common.6 For most testing methods, HbA1C is accurate in diabetics with HbAS or HbAC.6 In diabetics with clinically significant hemoglobinopathies, HbA1C does not accurately reflect glycemic control regardless of the testing method used.6 The most common clinically significant hemoglobinopathies include sickle cell disease, thalassemia, and hereditary spherocytosis (HS). In those with sickle cell disease (ie, HbSS, HbSC, HbCC) or HS, HbA1C is unreliable because the red cell life is reduced, thereby preventing glycosylation before HbA1C is removed from serum. In those with thalassemia or another Hb variant, 138
Felner and McGrath
red cell life is normal, but the amount of HbA1C is reduced.6 In African-Americans, the most common clinically significant hemoglobinopathy is HbSS, with a prevalence of 0.2 %.7 HPHF is an inherited disorder in which HbF persists throughout life.8 At birth, HbF accounts for up to 90% of the circulating Hb. Its synthesis declines during the third trimester, and it is gradually replaced by HbA over the first year of life. Few individuals with HPHF are identified with HbF, because they are asymptomatic. In HPHF, HbF accounts for ⬎ 20% of total Hb. Individuals with certain congenital or acquired disorders also may have elevated HbF levels, but still accounting for only 10% to 15% of total Hb. After the first year of life, the normal HbF value is ⬍ 1% of total Hb.9 In African-Americans, HPHF has a prevalence of only 0.02%.8,9 These 2 cases demonstrate how HPHF can interfere with the accurate measurement of HbA1C. In the immunoassay that we use (DCA 2000; Bayer HealthCare, Leverkusen, Germany), HbA1C is expressed as a percentage of total Hb, and the antibodies do not recognize non-HbA species.10 In those with Hb variants and normal Hb levels, the greater the percentage of non-HbA, the lower the HbA1C.10 This is the likely explanation as to why Case 1, who had more HbF (and less HbA), exhibited greater inconsistencies between HbA1C and mean SMBG level compared with Case 2. Both boys also had abnormal HbA1C levels at diagnosis but normal levels after initiation of insulin therapy; this is likely due to the significantly higher glucose levels before insulin therapy and also possibly to a mild variation of HbF and HbA over time. Many methods for evaluating HbA1C are available. For diabetics with Hb variants, published data are available regarding the accuracy of HbA1C testing methods.6 For diabetics with hemoglobinopathies, high-performance liquid chromatography (HPLC) is the most accurate technique for measuring HbA1C.10 Using HPLC, HbA1C percentages can be corrected by recalculating them as a percentage of total HbA; however, these corrections are not possible with the immunoassay method.10 The fructosamine test is another method used to assess glycemic control in diabetics with hemoglobinopathies; however, it provides glycemic assessment only over a short time frame (2 weeks), and its value in predicting long-term diabetic complications has not yet been evaluated.6 Diabetics with hemoglobinopathies should be monitored using an HbA1C testing method that yields reliable results. For all patients with diabetes, glycemic control should be assessed with frequent SMBG testing and the results correlated with HbA1C value.
REFERENCES 1. Eckfield JH, Bruns DE. Another step toward standardization of methods for measuring hemoglobin A1C [editorial]. Clin Chem 1997;43:1944-51. 2. John WG. Glycated haemoglobin analysis. Ann Clin Biochem 1997;34:17-31. 3. American Diabetes Association. Standards of medical care in diabetes. Diabetes Care 2007;30(Suppl 1):S4-41. 4. American Diabetes Association. Care of children and adolescents with type 1 diabetes. Diabetes Care 2005;28:186-212. 5. Weykamp CW, Penders TJ, Siebelder CW, Muskiet FA, van der Slik W. Interference of carbamylated and acetylated hemoglobins in assays of glycohemoglobin
The Journal of Pediatrics • July 2008
by HPLC, electrophoresis, affinity chromatography, and enzyme immunoassay. Clin Chem 1993;39:138-42. 6. Bry L, Chen PC, Sacks DB. Effects of hemoglobin variants and chemically modified derivatives on assays for glycohemoglobin. Clin Chem 2001;47: 153-63. 7. Ashley-Kock A, Yang Q, Olney RS. Sickle hemoglobin (Hb S) allele and sickle cell disease. Am J Genet 2000;151:839-45.
8. Hoyer JD, Penz CS, Fairbanks VF, Hanson CA, Katzmann JA. Flow cytometric measurement of hemoglobin F in RBCs. Am J Clin Pathol 2002;117:857-63. 9. Henney MM, Delgrosso K, Robinson R, Johnson CA, Daeschner CW, Campbell TA, et al. Interpretation of fetal hemoglobin only on newborn screening for hemoglobin. J Pediatr Hematol Oncol 2002;24:499-502. 10. Puukka R, Puukka M. Effect of hemoglobin F on measurements of hemoglobin A1C with physicians’ office analyzers. Clin Chem 1994;40:342-3.
Inaccurate Hemoglobin A1C Levels in Patients with Type 1 Diabetes and Hereditary Persistence of Hemoglobin F
139