First-Line Test for Hemoglobinopathy
The first-line test for suspected hemoglobinopathy is hemoglobin electrophoresis or high-performance liquid chromatography (HPLC), which should be performed in all newborns through universal newborn screening programs and in any patient with clinical suspicion based on microcytic anemia, family history, or ethnicity from high-prevalence regions. 1
Diagnostic Approach
Universal Newborn Screening
All 50 U.S. states, the District of Columbia, Puerto Rico, and the U.S. Virgin Islands have newborn screening programs capable of making a definitive diagnosis of sickle cell disease at birth 1. This represents the most critical first-line screening, as infants with hemoglobinopathies are healthy at birth but develop symptoms as fetal hemoglobin declines in early infancy.
First-Line Laboratory Methods
For suspected hemoglobinopathy in children or adults, the initial testing should include:
- Complete blood count (CBC) with red blood cell indices looking specifically for microcytic hypochromic anemia (MCV <80 fL is typical) 2, 3
- Hemoglobin electrophoresis (alkaline pH) or cation-exchange HPLC as the primary diagnostic method 4, 5
- Peripheral blood smear examination for characteristic red cell morphology 2
The HPLC method has become the preferred first-line test in most laboratories because it provides quantitative measurement of hemoglobin A2 and F, which are critical for distinguishing between different hemoglobinopathies 4, 6. Hemoglobin A2 ≥4.0% discriminates between sickle cell anemia and sickle β-thalassemia with 95.2% sensitivity and 96.5% specificity 4.
Confirmatory Testing Algorithm
When HPLC or electrophoresis identifies an abnormal hemoglobin pattern:
For sickle cell variants: Perform sickling test (100% sensitivity) and alkaline pH electrophoresis for confirmation 4
For suspected hemoglobin variants: Targeted sequencing of globin genes is the most efficient diagnostic approach 7
For suspected methemoglobinemia (a specific hemoglobinopathy): The key diagnostic tests are:
- MetHb level measurement by co-oximetry on blood gas analysis
- Cytochrome b5 reductase enzymatic activity measurement
- DNA analysis for confirmation 7
Critical Pitfalls to Avoid
Hemoglobin variants can interfere with HbA1c measurements, causing spuriously high or low results with ion-exchange HPLC 8. With over 700 hemoglobin variants reported, unsuspected errors may occur. If HbA1c results seem inconsistent with clinical picture, suspect a hemoglobin variant and use boronate affinity chromatography instead 8.
Do not rely solely on point-of-care tests or solubility tests (like sickle solubility tests) for definitive diagnosis—these must always be followed by confirmatory HPLC or electrophoresis 5.
When Molecular Testing is Needed
Molecular analysis (DNA sequencing) should be performed when:
- HPLC/electrophoresis results are ambiguous or show unusual patterns
- Precise characterization is needed for genetic counseling
- Prenatal diagnosis is being considered
- Complex compound heterozygous states are suspected 4, 2
Molecular testing is considered the gold standard for hereditary methemoglobinemia diagnosis 7, but for most common hemoglobinopathies like sickle cell disease and thalassemia, HPLC combined with hemogram data and sickling test provides reliable characterization without requiring molecular analysis 4.
Special Populations
Pregnant women: Should be screened according to NHS Sickle Cell and Thalassaemia Screening Programme guidelines, with laboratories using methods capable of quantitating hemoglobins A2 and F at required cut-off points, with provisional results available within 3 working days 5.
Preoperative patients: Those from ethnic groups with significant hemoglobinopathy prevalence should undergo screening for sickle cell disease 5.
Infants under 1 year arriving in the U.K.: Should be offered screening for sickle cell disease regardless of newborn screening status 5.