Differential Diagnosis of Anemia Using the Erythrocyte Filterability Method.

Hereditary hemolytic anemias (HHAs) have very similar clinical manifestations, complicating differential diagnosis and determining treatment strategies, such as splenectomy. To differentiate between hereditary spherocytosis (HS), pyruvate kinase deficiency (PKD), and hereditary stomatocytosis (HSt), we proposed measuring erythrocyte filterability using membrane filters with a pore diameter of 3 or 3.5 μm. Our modified method provides improved reproducibility, reducing the scattering in results caused by differences in the filters used. Erythrocytes' filterability differs significantly between patients with HS, HSt, and PKD (medians and 95% confidence intervals were 0.025 [0.004; 0.100] (n = 86); 0.645 [0.520; 0.730] (n = 10), and 0.760 [0.700; 0.782] (n = 26), respectively). The specificity of the filterability test for the HS diagnosis was 99.1%, comparable with the best available tests, while its sensitivity (85.4%) was slightly lower than that of some alternative methods. Only the filterability test was able to identify a second subgroup of HS patients (14.0%) with higher filterability (close to normal), but the diagnosis of HS in these patients could be confirmed by reduced filterability on a 3-μm filter. This subgroup requires further detailed study. The proposed method for measuring filterability is promising for diagnosing HS. It has high sensitivity and specificity and can be performed quickly without expensive equipment.