ACLS
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Edwards, H. D.
Right arrow Articles by Shihabi, Z. K.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Edwards, H. D.
Right arrow Articles by Shihabi, Z. K.
Annals of Clinical & Laboratory Science 39:32-37 (2009)
© 2009 Association of Clinical Scientists

Rapid Quantitation of Hemoglobin S in Sickle Cell Patients Using the Variant II Turbo Analyzer

Henry D. Edwards, Hernan Sabio and Zak K. Shihabi
Departments of Pathology and Pediatrics, Wake Forest University School of Medicine, Winston-Salem, North Carolina

Address correspondence to Zak K. Shihabi, Ph.D., Department of Pathology, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA; tel 336 716 2639; fax 336 716 9944; e-mail zshihabi{at}wfubmc.edu.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
A rapid (~90 sec), fully automated method is described for quantifying hemoglobin S (HbS) by high performance liquid chromatography (HPLC) using the Bio-Rad Variant II Turbo analyzer. Although this instrument is designed to quantify only blood hemoglobin A1c (HbA1c), we show that it can also quantify accurately, without modification, HbS levels in sickle cell patients, provided the blood samples meet certain conditions. The samples should contain detectable hemoglobin F (HbF), but should not contain hemoglobin C (HbC). Under these conditions, blood HbS levels obtained by this method correlate well with those obtained by agarose electrophoresis (r2 = 0.97, n = 81 patients). We also show that quantitation of blood HbF in sickle cell patients is more accurate by this method than by agarose electrophoresis when the HbF level is in the range from 0.2 to 10%.

Keywords: hemoglobinopathies, sickle cell disease, fetal hemoglobin, glycated hemoglobin, hemoglobin quantification, electrophoresis, HPLC, HbA1c


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
One of the mainstays of treatment for patients with sickle cell disease is the administration of therapeutic blood transfusions. In addition to correcting the underlying anemia, this intervention is effective in reducing the complications of the disease by lowering the fraction of HbS in the circulation [1–7]. This treatment can prevent sickle cell related complications (eg, stroke, recurrent acute chest syndrome) and reduce the risk of peri- and postoperative complications of surgical procedures. Many studies recommend decreasing the HbS level in these patients to <60% or even to <30% [2–5]. In some studies, patients undergoing surgical procedures who were pre-transfused to a goal of HbS <60% suffered fewer peri- and post-operative complications than did controls who had no transfusion, whereas the more aggressive goal of HbS <30% did not provide additional benefit [5].

These studies point to the need for accurate and rapid methods to quantify pre- and post-transfusion HbS levels for improving the outcome in patients with sickle cell disease [5,8,9]. Three general techniques are used to quantify HbS. The most common is agarose gel electrophoresis [10]. This is a time-consuming technique (~2 hr), which makes it difficult and expensive to perform on an emergency basis. The second method is HPLC based on ion exchange chromatography [11,12]. This method is faster (5 to 10 min) than agarose electrophoresis, but the instrumentation is more expensive [7]. The most recent method is capillary electrophoresis, which is rapid (5–15 min) and more accurate than agarose electrophoresis [13]. However, the instrument is not popular because it is very expensive and relatively new.

This study describes how HbS can be reliably quantified using a Bio-Rad HPLC instrument that is designed mainly for the determination of blood HbA1c. The instrument is fully automated, rapid (~90 sec), suited for emergency use, and commonly available in clinical laboratories. According to the recent surveys of the College of the American of Pathologists, more than twice as many laboratories use ion exchange chromatography for quantification of HbA1c than those that use electrophoresis for quantification of hemoglobin variants (~700 vs 300). Since the Bio-Rad instrument was not designed or approved for quantitation of HbS, one objective of this work was to explore the factors and pitfalls that affect HbS assays using this analyzer.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
HPLC instrument  The VariantTM II Turbo (Bio-Rad Laboratories, Hercules, CA) instrument is an automated HPLC that is designed and approved only to separate and quantify HbA1c based on cation exchange chromatography without sample pretreatment. Whole blood is aspirated into the instrument. The red blood cells are hemolyzed and injected onto a short ion exchange column to separate hemoglobin A into fractions with different retention times, such as: HbA1c (glycated), C Hb (carbamyl Hb), L A1C (labile Hb), and P3 (acetylated Hb), based on charge differences. However, other hemoglobin variants such as HbF and HbS also separate based on their respective charges. The different hemoglobins and the various Hb fractions are eluted by a special buffer gradient of increasing ionic strength. Identification of hemoglobin variants by the instrument software depends on their specific retention times (capacity factor), as monitored by a spectrophotometric detector. The buffer gradient can be changed to a different one in order to elute better the different hemoglobin variants, but changing the buffer is inconvenient in routine analysis.

Patients and study protocol  This study was performed in our routine clinical chemistry laboratory on blood samples that were obtained from sickle cell patients for quantitation of HbS by agarose electrophoresis as part of their management. The left-over samples were used for analysis by HPLC for comparison. This study was done under IRB approval of exempt status using the left-over portion of blood samples.

Instrument calibration.  The Variant II Turbo instrument was calibrated on a daily basis for HbA1c using the manufacturer’s calibrators and instructions. Two HbA1c controls (low and high) were used to check the analytical precision.

Linearity and recovery studies.  Linearity studies were performed by mixing blood samples with high and low levels of HbS and HbA (five point linearity check), taking into account the integration counts, too. The aim of the recovery study was to explain the observed bias in HbF quantitation by HPLC vs agarose electrophoresis. Hemoglobin F in a leftover blood sample from a 4-day-old normal HbA infant was quantified by agarose electrophoresis and then diluted with 2 different samples that did or did not contain HbS, as described in Table 1Go, to bring the HbF levels to 4.2 %.


View this table:
[in this window]
[in a new window]

  		Table 1. Interference of HbS in electrophoretic quantitation of HbF as shown by recovery data in 2 patients with different levels of HbS (0% and 58%).
 
Carryover.  The carryover of HbS in the HPLC method was measured by assay of samples free of HbS immediately after samples with high HbS levels (>75%). The percentage of HbS carryover was measured as the (false) increase of HbS in the samples free from HbS.

Agarose electrophoresis.  The semi-automated alkaline agarose gel electrophoresis system of Sebia, Inc. (Norcross, GA) is the method routinely used in our laboratory to quantitate HbS and screen for other hemoglobin variants. Samples were prepared and hemoglobin was separated and quantified according to the manufacturer’s procedure. This method requires about 2 hr for analysis. The precision (CV) for HbS assay is 2.9% (mean = 17%, n = 10).


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
Hemoglobin variant detection by HPLC is seldom performed in routine clinical laboratories because of the small number of samples and the relatively high cost of the instrument. On the other hand, use of the Bio-Rad HPLC instrument with a fast elution gradient and different software for analysis of HbA1c is much more common. We noticed that if two major problems are addressed, the instrument can give reliable quantification for hemoglobins S, F and A: First, the blood sample should not contain HbC; and second, HbF should be detectable directly by the instrument. Under these conditions, the correlation of HbS levels in 81 patients by the HPLC assay and by agarose electrophoresis is very good (correlation coefficient r2 = 0.97; Fig 1Go).


Figure 1
View larger version (21K):
[in this window]
[in a new window]

  		Fig. 1. Correlation of HbS assays by HPLC and electrophoresis (n = 81 patients).

 
HbS values outside the range from ~5 to 95% exhibit slight differences that are of academic concern rather than clinical concern and can be reported as such. Both instruments have their own limitations for quantification of values at the extremes, with agarose electrophoresis being more affected than HPLC. Quantification by electrophoresis has many limitations [14] especially for small bands such as HbA2 [15] and HbF. At very low levels these bands become undetectable or sometimes change their migration [16]. Denatured hemoglobin migrates in front but very close to the different hemoglobins, rendering peak integration difficult. The HPLC instrument, as measured in this study, suffers from a carry-over of 4.7%.

Although the major emphasis in transfusion of sickle cell disease patients is on quantitation of HbS itself [1–5,17], it is also helpful to quantify HbA and HbF in these patients. For example, quantitation of hemoglobin F is very important in sickle cell patients treated with hydroxyurea. When HbF is ≤10 % by HPLC (or ≤ 15% by electrophoresis), it elutes as a sharp single HPLC peak over a 5 sec period, (Fig 2Go, middle panel), which is identifiable as HbF by the instrument. On the other hand, when HbF is ≥10 % it elutes over a 10 sec period as a wide peak that overlaps, co-migrates, and interferes with the labile fraction and HbA1c peaks. Under this condition (Fig. 2Go, top panel) the instrument erroneously identifies HbF as the labile fraction. Thus, whenever HbF is not identified, the sample should be analyzed by electrophoresis or the chromatogram examined for the absence of HbF (based on the retention time of HbF (Fig. 2Go, bottom panel) or the presence of elevated (>10%) labile hemoglobin.


Figure 2
View larger version (23K):
[in this window]
[in a new window]

  		Fig. 2. (Top panel): HPLC of a sample with HbF level of >10% (arrow). (Middle panel): HPLC of a sample with HbF level of 0.7% (arrow). (Bottom panel): HPLC of a sample with HbF level of 0% (arrows: HbF retention time = 0.27 min). The shaded peak in each panel is HbA1c.

 
A large labile hemoglobin peak (>10%) on samples collected recently is an indication of elevated HbF (Fig. 2Go, top panel). Such samples can be confirmed and re-analyzed on the HPLC instrument after mixing with an adult sample (low HbF in absence of HbS). The majority of adult sickle cell patients have HbF levels of 0.2–10% [18] which the HPLC instrument can identify and quantify directly and accurately (Fig. 3Go). The correlation coefficient for HbF analyses by HPLC vs agarose electrophoresis in sickle cell patients with HBF of <10% is good (r2 = 0.89). However, the regression analysis for patients with HbS yields a slope of 0.72. In other words, the HbF values by HPLC average about 30% less than those by agarose electrophoresis for patients with HbS.


Figure 3
View larger version (20K):
[in this window]
[in a new window]

  		Fig. 3. Correlation of HbF assays by HPLC and electrophoresis for 43 patients with HbS.

 
Fig. 4Go shows that the area under the F peak by electrophoresis is falsely affected by the HbS area. Almost one-third of the area under the F peak belongs to that of HbS. The % HbF for the sample in Fig. 4Go is 9.7% by electrophoresis, but only 5.9% by HPLC. The artefactitious increase in HbF by electrophoresis causes an equivalent false decrease in the area of HbS; however, because the HbS level is usually high this effect is not as significant as that for HbF.


Figure 4
View larger version (16K):
[in this window]
[in a new window]

  		Fig. 4. Electrophoresis of a blood sample containing HbS (43%) and HbC (42.4%) illustrating an apparent increase in the area of HbF (9.7%). The dotted line indicates the projected corrected area.

 
To confirm this observation further, a known amount of HbF (4.2%) was added to two samples very low in HbF; one contained HbS and the other did not (only HbA), Table 1Go. The sample that contained HbS showed a falsely elevated recovery of HbF (141%) in the electrophoretic method while it yielded a slightly lower recovery (89%) in the HPLC method. The recovery was almost the same by the two methods for the sample that contained only HbA, indicating that the artefactitious increase in HbF by electrophoresis is not observed in patients with HbA. These problems are primarily due to the the software of the agarose electrophoresis method, which does not take into account the changes in peak shape in the presence of HbS. Furthermore, agarose electrophoresis does not detect HbF levels <2%. HbF <10% is correctly identified by the HPLC method and quantified more accurately than by electrophoresis. In other words, as long as HbF is identified by the HPLC instrument, the quantitation of this hemoglobin is accurate.

When HbS and HbF are both identified in a blood sample, % HbA can be calculated by subtraction of these two fractions from 97.5% (with 2.5 % accounting for the average level of HbA2). In this case, the indirect quantitation of HbA by HPLC correlates well with the results obtained by agarose electrophoresis (Fig. 5Go).


Figure 5
View larger version (19K):
[in this window]
[in a new window]

  		Fig. 5. Correlation of %HbA levels calculated from HPLC data and those obtained by electrophoresis (n = 81 patients).

 
The decrease of HbS in sickle cell patients before and after transfusion is similar by both the HPLC and electrophoretic methods (Fig. 6Go), with minor differences in some patients probably attributable to the difference in integration of HbF (and consequently in HbS) by electrophoresis, as noted previously.


Figure 6
View larger version (32K):
[in this window]
[in a new window]

  		Fig. 6. Comparison of % HbS change before and after transfusion in 8 patients, as assayed by HPLC vs agarose electrophoresis (AE).

 
The HPLC instrument was calibrated daily for HbA1c quantification. Two controls (low and high) were run to monitor analytical precision for HbA1c, (CV = 2.2% , mean level = 9.72%, n = 34; and CV = 2.3%, mean level = 5.75%, n = 34). The respective CVs of HbS and HbF assays by HPLC (n = 16) were 0.9% (mean level = 43%), and 4.3% (mean level = 1.35%). The CV for HbS assay was 2.9% by agarose electrophoresis (mean level = 17%). The reproducibility (CV) of retention times by HPLC for HbF and HbS (n = 16) were 0.57% and 0.47%, respectively. Based on mixing blood samples (five-point linearity) with different HbS concentrations, HbS analysis by HPLC was linear (r2 = 0.989) between 5 and 95%. However, levels of HbA below 7% are reported as <7%.

Sample carryover for the HPLC instrument averaged 4.7%. This carry-over is not important in HbA1c analysis due to the narrow range of observed values, but it is more important in quantitation of hemoglobin variants because of their wider ranges of values. For blood samples with <6% HbS (or other Hb variant), the HPLC analysis should be repeated after assay of a normal sample.


   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
HbS can be quantified by the Variant II Turbo instrument provided the blood sample meets specific conditions. Here we show that this HPLC instrument with the fast gradient for HbA1c analysis can accurately separate, identify, and quantify HbS if certain precautions and quality assurance practices are observed. There are 3 major problems in quantitation of HbS by the HPLC technique: First, hemoglobin C co-migrates with HbS. Second, HbF sometimes is not detected because it is too low (<0.2% ) or too high (>10%). When the HbF level is high, it co-migrates with the labile fraction and is identified by the instrument as labile fraction. Third, HbA is detected indirectly because the instrument is designed to separate HbA into several fractions in order to quantify HbA1c.

HbC is detected and identified by the HPLC instrument as HbC when present by itself or in combination with HbA. Blood samples with both HbS and HbC are identified by the HPLC software as HbS. Therefore, it is important not to use this instrument for quantification of unknown patients but to restrict it to those who are definitely known to have HbS. Many patients with sickle cell disease require repeated or chronic transfusions, such as in the management of stroke or risk for stroke. It is for these patients who have been previously identified as having HbS and who are regularly transfused that the described procedure may be of greatest benefit. For patients with HbS and HbC, one alternative is to report the data as a sum of Hb (S+C) especially since the change in %HbA (pre- and post-transfusion) is most meaningful.

When HbF is identified by the HPLC instrument, the quantification of this hemoglobin is more accurate by HPLC than by agarose electrophoresis. Usually this identification occurs when the HbF level is 0.2 to 10%. Outside this range, the HPLC software does not recognize HbF and the sample either has to be analyzed by another technique or the chromatogram examined carefully. HbA level is quantified indirectly by subtraction (97.5 – (% HbS + HbF)), as indicated above.

Previously, Higgins et al [19,20] and Thomas et al [21] showed that HPLC techniques for HbA1c, with different gradients, can be used for rapid screening for Hb variants. Here we demonstrate that the BioRad Variant II Turbo HPLC method for HbA1c, without modification, can be used to detect HbS and quantify it accurately in ~90 sec, fully automated, and without any sample treatment. However, the quantitation presents a different type of challenge compared to the screening. Unless they are carefully addressed, several problems can lead to unreliable results as we pointed out.

In addition to speed and automation, the HPLC technique offers several other advantages in quantifying HbS. Agarose electrophoresis is designed for analysis of multiple samples simultaneously (batching). Running single samples by agarose electrophoresis is expensive for labor and materials. On the other hand, these expenses in HPLC are not affected by running single samples. For the consumables alone, electrophoresis is ~4 times more expensive than HPLC. Finally, the HPLC method entails less sample manipulation, which reduces the chance for errors.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Yale SH, Nagib N, Guthrie T. Acute chest syndrome in sickle cell disease. Postgrad Med 2000;107:215–222.[Medline]
  2. Adams RJ, McKie VC, Hsu L, Files B, Vichinsky E, Pegelow C, Abboud M, Gallagher D, Kutlar A, Nichols FT, Bonds DR, Brambilla D. Prevention of a first stroke by transfusions in children with sickle cell anemia and abnormal results on transcranial doppler ultrasonography. NEJM 1998;339:5–11.[Medline]
  3. Pegelow CH, Adams RJ, McKie VC, Abboud M, Berman B, Miller ST, Olivieri N, Vichinsky E, Wang W, Brambilla D. Risk of recurrent stroke in patients with sickle cell disease treated with erythrocyte transfusions. J Pediatrics 1995;126:896–899.[Medline]
  4. Cohen AR, Martin MB, Silber JH, Kim HC, Ohene-Frempong K, Schwartz E. A modified transfusion program for prevention of stroke in sickle cell disease. Blood 1992;79:1657–1661.[Abstract/Free Full Text]
  5. Vichinsky EP, Haberkern CM, Neumayr L, Earles AN, Black D, Koshy M, Pegelow C, Abboud M, Ohene-Frempong K, Iyer RV. A comparison of conservative and aggressive transfusion regimens in the perioperative management of sickle cell disease. NEJM 1995;333:206–213.[Medline]
  6. Rosse WF, Gallagher D, Kinney TR, Castro O, Dosik H, Moohr J, Wang W, Levy PS. Transfusion and alloimmunization in sickle cell disease. Blood 1990;76: 1431–1437.[Abstract/Free Full Text]
  7. Kozarski TB, Howanitz PJ, Howanitz JH, Lilic N, Chauhan YS. Blood transfusions leading to apparent hemoglobin C, S, and O-Arab hemoglobinopathies. Arch Pathol Lab Med 2006;130:1830–1833.[Medline]
  8. Yale SH, Nagib N, Guthrie T. Acute chest syndrome in sickle cell disease. Postgrad Med 2000;107:215–222 .[Medline]
  9. Kozanoglu I, Boga C, Ozdogu H, Sezgin N, Kizilkilic E, Kural M. Automated red cell exchange procedures in patients with sickle cell disease. Transfus Apher Sci 2007;36:305–312.[Medline]
  10. Lepp CA, Bluestein BI. Hemoglobin electrophoresis at alkaline pH on agarose gels. Clin Chem 1978;24:936–937.[Abstract/Free Full Text]
  11. Joutovsky A, Hadzi-Nesic J, Nardi MA. HPLC retention time as a diagnostic tool for hemoglobin variants and hemoglobinopathies: A study of 60000 samples in a clinical diagnostic laboratory. Clin Chem 2004;50:1736–1747.[Abstract/Free Full Text]
  12. Papadea C, Cate JC. Identification of quantification of hemoglobins A, F, S, and C by automated chromatography. Clin Chem 1996;42:57–63.[Abstract/Free Full Text]
  13. Shihabi ZK. Clinical application of capillary electrophoresis. In: Handbook of Capillary and Microchip Electrophoresis and Associated Microtechniques, (Landers J, Ed), CRC Press, Boca Raton, 2008; pp 785–810.
  14. Zak B, Baginski, ES, Epstein E. Associated problems of protein electrophoresis, staining and densitometry. Ann Clin Lab Sci 1978;5:385–395.
  15. Shihabi ZK, Hinsdale ME, Daugherty HK Jr. Hemoglobin A2 quantification by capillary zone electrophoresis. Electrophoresis 2000;21:749–752.[Medline]
  16. Shihabi ZK. Effect of sample composition on electrophoretic migration application to hemoglobin analysis by capillary electrophoresis and agarose electrophoresis. J Chromatogr A 2004;1027:179–184.[Medline]
  17. Mehta SR, Adams RJ. Treatment and prevention of stroke in children with sickle cell disease. Curr Treat Options Neurol 2006;8:503–512.[Medline]
  18. Mehta SR, Aenyi-Annan A, Byrns PJ, Lottenberg R. Opportunities to improve outcomes in sickle cell disease. Am Fam Physician 2006;74:303–312.[Medline]
  19. Higgins TN, Ridley B, Clarke G. Novel method for screening for the presence of haemoglobin S in blood. Transfusion Med 2005;15:493–497.[Medline]
  20. Higgins TN, Ridley B. Tentative identification of hemoglobin variants in the Bio-Rad VARIANT II Hb A1c method. Clin Biochem 2005;38:272–277.[Medline]
  21. Thomas LB, Agosti SJ, Man MA, Mastorides SM. Screening for hemoglobinopathies during routine hemoglobin A1c testing using the Tosoh G7 glycohemoglobin analyzer. Ann Clin Lab Sci 2007,37:251–255.[Abstract/Free Full Text]



This article has been cited by other articles:


Home page
 CJASNHome page
A. J. Bleyer, S. V. Reddy, L. Sujata, G. B. Russell, D. Akinnifesi, A. J. Bleyer Jr., D. Hire, Z. Shihabi, M. A. Knovich, P. Daeihagh, et al.
Sickle Cell Trait and Development of Microvascular Complications in Diabetes Mellitus
Clin. J. Am. Soc. Nephrol., June 1, 2010; 5(6): 1015 - 1020.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Edwards, H. D.
Right arrow Articles by Shihabi, Z. K.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Edwards, H. D.
Right arrow Articles by Shihabi, Z. K.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS