When to Perform DNA Analysis After Hemoglobin Analysis
DNA analysis should be performed immediately after hemoglobin analysis when abnormal hemoglobin variants are detected (HbS, HbC, or elevated HbA2 suggesting thalassemia trait), particularly in patients from high-prevalence populations or with family history of hemoglobinopathies. 1
Indications for DNA Testing After Abnormal Hemoglobin Analysis
Primary Triggers for Genetic Testing
Perform DNA analysis when hemoglobin electrophoresis shows HbS peak to distinguish between sickle cell trait (HbAS), sickle cell disease (HbSS), or compound heterozygous states like HbSC or HbS-β-thalassemia 2, 3
Order genetic testing when elevated HbA2 (>3.5%) is detected, as this indicates β-thalassemia trait and requires mutation analysis to determine specific genotype 4, 5
Initiate DNA analysis when hemoglobin analysis shows abnormal patterns but the specific variant cannot be definitively identified by electrophoresis alone 1
Partner and Family Testing Algorithm
When a pregnant woman is identified as a hemoglobinopathy carrier, the partner must be tested immediately to determine fetal risk 1. The algorithmic approach is:
- If partner testing is negative → reassure couple, no further testing needed 1
- If partner is also a carrier → proceed to prenatal diagnosis discussion 1
- For first-degree relatives of confirmed cases → perform simultaneous genotype (HFE/hemoglobin mutation analysis) and phenotype (hemoglobin electrophoresis) testing at a single visit 1
Specific Clinical Scenarios Requiring DNA Analysis
Newborn screening showing "FS" pattern requires confirmatory DNA sequencing to distinguish sickle cell disease from compound heterozygous states like HbS-(δβ)⁰-thalassemia, even with negative family history 3
Patients with microcytic anemia and abnormal hemoglobin electrophoresis showing both HbS peak and elevated HbA2 require molecular study for both sickle cell mutation (codon 6 A>T) and common β-thalassemia mutations 2
Symptomatic patients with suspected hemoglobinopathy (chronic anemia, bone pain, splenomegaly) should have DNA analysis performed after initial hemoglobin studies show abnormalities to establish definitive diagnosis 2, 6
Pre-Test Counseling Requirements
Before ordering DNA analysis, discuss with patients 1:
- Available treatment options and their efficacy
- Costs of genetic testing
- Social implications including disease labeling and insurability
- Psychological impact of diagnosis
- Possibility of identifying novel or as-yet-unknown genotypes
Genotype-Specific Management Implications
The specific DNA diagnosis directly impacts disease severity and management strategy 7:
- HbSS (sickle cell anemia): Most severe phenotype, hemoglobin 60-90 g/L, requires aggressive preventive measures 7
- HbSC disease: Higher baseline hemoglobin, generally fewer symptoms but still requires careful management 7
- HbS-β-thalassemia: Clinical heterogeneity depending on β-thalassemia mutation type (β⁰ vs β⁺), with IVS-I-110 (G→A) being most common 4
Common Pitfalls to Avoid
Do not rely on hemoglobin electrophoresis alone for definitive diagnosis, as over 200 different β-thalassemia mutations exist with varying clinical severity 2, 5
Do not assume negative family history excludes hemoglobinopathy - rare compound heterozygous states can occur in patients without known family history 3
Remember that sickle cell trait (HbAS) can interfere with A1C testing, causing falsely low values by approximately 0.3%, requiring alternative glucose monitoring methods 8