Can an elevated reticulocyte (reticulocyte count) count interfere with the Glucose-6-Phosphate Dehydrogenase (G-6-PD) assay?

Elevated Reticulocyte Count and G-6-PD Assay Interference

True. An elevated reticulocyte count can interfere with the G-6-PD assay, potentially causing falsely normal results in G-6-PD deficient patients.

Mechanism of Interference

• Reticulocytes contain significantly higher amounts of G-6-PD enzyme than mature erythrocytes 1
• In patients with hemolytic conditions, reticulocytosis can mask underlying G-6-PD deficiency by elevating the overall measured enzyme activity 2
• This interference is particularly problematic in:
  • Neonates with physiologic reticulocytosis
  • Patients with hemolytic anemia
  • Patients recovering from acute blood loss
  • Patients responding to treatment for anemia

Clinical Evidence

• According to the American Society of Hematology guidelines, reticulocytosis can significantly impact G-6-PD activity measurements 1
• In pyruvate kinase deficiency studies, researchers have observed that reticulocyte-rich blood can mask enzyme deficiencies, which applies similarly to G-6-PD testing 2
• In G-6-PD deficient patients with high reticulocyte counts, the G-6-PD activity may fall within reference limits despite the underlying deficiency 2

Detection Strategies

To mitigate this interference and improve diagnostic accuracy:

1. Compare enzyme ratios: Calculate the ratio of G-6-PD activity to another age-dependent enzyme (similar to PK/HK ratio approach) 2
2. Flow cytometric assay: This method has shown better reliability in detecting G-6-PD deficiency in the presence of reticulocytosis compared to spectrophotometric methods 3
3. Genetic testing: For definitive diagnosis in cases with suspected interference, molecular analysis for common G-6-PD mutations is recommended 4

Clinical Implications

• Misdiagnosis of G-6-PD deficiency due to reticulocytosis can lead to:
  • Inappropriate administration of oxidative drugs
  • Unexpected hemolytic crises
  • Severe hyperbilirubinemia in neonates 2
  • Delayed appropriate management

Recent Research Findings

While the traditional understanding has been that reticulocytosis interferes with G-6-PD assays, some recent studies have challenged this view:

• A 2022 study found that reticulocytosis did not have a statistically significant effect on the detection of G-6-PD deficiency in newborns using both qualitative and quantitative methods 5
• However, this finding contradicts established clinical practice and earlier research, so caution is still warranted 2, 1

Best Practice Recommendations

• When G-6-PD deficiency is suspected but test results are normal or borderline:
  • Consider the reticulocyte count when interpreting G-6-PD assay results
  • Repeat testing when reticulocyte count normalizes
  • Consider molecular testing for definitive diagnosis in critical cases
  • Use flow cytometric methods when available for more accurate assessment 3

The interference of reticulocytosis with G-6-PD assay results remains an important clinical consideration that can impact patient management and outcomes, particularly in preventing severe hemolytic episodes.