The frequency of occurrence of fish-shaped red blood cells in different haematologic disorders

Background: Red blood cells (RBC) resembling the silhouette of a fish are rarely observed in peripheral blood (PB) smears. In this study, we determined the frequency of occurrence of fish-shaped RBC in different haematologic diseases. Methods: We examined PB smears of patients with iron deficiency anaemia (IDA) (n = 23), beta-thalassaemia minor (BTM) (n = 30), sickle cell disease (SCD) (n = 7), autoimmune haemolytic anaemia (AIHA) (n = 13), microangiopathic haemolytic anaemia (MAHA) (n = 11), hereditary sphaerocytosis (HS) (n = 4), hereditary elliptocytosis (HE) (n = 3), vitamin B12 and folate deficiency (n = 15), anaemia in liver disease (LD) (n = 17), myelodysplastic syndrome (MDS) (n = 15), acute myeloid leukaemia (AML) (n = 29), chronic myeloid leukaemia (CML) (n = 18), primary myelofibrosis (PMF) (n = 12), chronic myelo-monocytic leukaemia (CMML) (n = 15) and 21 healthy controls by light microscopy for the occurrence of fish-shaped erythrocytes. The fish-shaped RBC were counted as cells per 20 high-power fields (HPF) at 1000-fold magnification, and slides containing >= 1 fish-shaped RBC/20 HPF were regarded as positive. Results: Fish-shaped RBC were significantly found in HE, iron deficiency, vitamin B12/folate deficiency, LD and PMF. The highest numbers of fish-shaped RBC were seen in HE and vitamin B12/folate deficiency. In patients with BTM, MDS, AML and CMML, this RBC anomaly was only occasionally observed. Furthermore, a statistically significant negative correlation of haemoglobin with the occurrence of fish-shaped RBC was apparent (p < 0.014). Conclusions: Our data show that the occurrence of fish-shaped RBC is suggestive of a pathologic condition, especially IDA, HE, vitamin B12 or folate deficiency, primary mylofibrosis or LD, and is significantly associated with severity of anaemia.