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

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.

We examined PB smears of patients with iron deficiency anaemia (IDA) (n=23), β-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.

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).

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.