Faculty Bibliography

BACKGROUND: Previous evaluations of HPLC as a tool for detection of hemoglobin variants have done so within newborn-screening programs and/or by use of stored samples. We describe a 32-month prospective study in a clinical diagnostic laboratory in which we evaluated the imprecision of HPLC retention times and determined the retention times for hemoglobin variants seen in a multiethnic setting. METHODS: We analyzed all samples on the Bio-Rad Variant II HPLC system. For normal hemoglobin fractions and hemoglobin variants, we recorded and analyzed their retention times, their proportion of the total hemoglobin (%), and the peak characteristics. We compared the imprecision of retention time with the imprecision of retention time normalized to the retention time of hemoglobin A0 (Hb A0) and to the retention time of Hb A2. Alkaline and acid hemoglobin electrophoresis, and in certain cases globin chain electrophoresis, isoelectric focusing, and DNA analysis, were performed to document the identities of the hemoglobin variants. RESULTS: The mean (SD) imprecision (CV) of the retention time was 1.0 (0.7)% with no statistical difference compared with the imprecision for normalized retention times. Among 60,293 samples tested, we encountered 34 unique hemoglobin variants and 2 tetramers. Eighteen variants and 2 tetramers could be identified solely by retention time and 3 variants by retention time and proportion of total hemoglobin. Four variants could be identified by retention time and peak characteristics and eight variants by retention time and electrophoretic mobility. One variant (Hb New York) was missed on HPLC. Retention time on HPLC was superior to electrophoresis for the differentiation and identification of six members of the Hb J family, four members of the Hb D family, and three variants with electrophoretic mobilities identical or similar to that of Hb C. Six variants with electrophoretic mobilities identical or similar to that of Hb S could be differentiated and identified by retention time and proportion of total hemoglobin. HPLC detected two variants (Hb Ty Gard and Hb Twin Peaks) missed on electrophoresis. CONCLUSIONS: The retention time on HPLC is reliable, reproducible, and in many cases superior to conventional hemoglobin electrophoresis for the detection and identification of hemoglobin variants. Confirmatory testing by electrophoresis can be eliminated in the majority of cases by use of retention time, proportion of total hemoglobin, and peak characteristics of HPLC

CONTEXT: Current standards for laboratory accreditation from the College of American Pathologists state that when high-performance liquid chromatography (HPLC) is used as a screening test, all non-A, non-S abnormal hemoglobin (Hb) variants must be confirmed by an alternative method, including alkaline and acid electrophoresis. OBJECTIVE: To determine whether confirmation of Hb C and Hb O-Arab variants by an alternative method is required when using the Bio-Rad Variant II HPLC system. DESIGN: We reviewed 48 478 consecutive hemoglobin identification test results performed on the Bio-Rad Variant II HPLC system during the period November 15, 2000 to January 15, 2003. SETTING: Special Hematology Laboratory, Department of Pathology, Bellevue Hospital Center, New York, NY. MAIN OUTCOME MEASURES: The chromatogram patterns and retention times (RTs) for specimens containing Hb C and Hb O-Arab were analyzed. We compared the results by the HPLC method with those by the confirmatory tests (alkaline and acid electrophoresis) for both variants. RESULTS: We identified 3668 cases of abnormal hemoglobin variants, including 660 cases of Hb C trait (17%), 5 cases of Hb O-Arab trait (0.1%), and 1 case of Hb SO-Arab (0.03%). A unique pattern of separation on the chromatogram for Hb O-Arab was revealed, presenting as 2 distinct peaks in 2 different manufacturer-defined RT windows, namely, D and C. The chromatogram for Hb C did not show the D window in any of the reviewed cases. The RT in the C window (C-RT) revealed a statistically significant difference for Hb C and Hb O-Arab (5.18 +/- 0.01 minutes and 4.91 +/- 0.01 minutes, respectively; P <.001). CONCLUSION: According to our review, the identification of Hb C and Hb O-Arab is accurate using HPLC methodology, as performed by the Bio-Rad Variant II HPLC system. This method can be both confirmatory and diagnostic at the same time