Background and Aims Recently echinocytosis and subsequent haemolytic anaemia was described in a premature infant receiving omega-3 fatty acids (Omegaven) in parenteral nutrition. It was presumed that omega-3 fatty acids caused echinocytosis. No study has been done to compare the effect of different fatty acids used in parenteral nutrition on human red blood cell (RBC) morphology. We therefore studied the effect of omega-3 fatty acids (Omegaven) and omega –6 fatty acids (Intralipid) at different concentrations on RBC in vitro.

Methods Blood samples were obtained from 12 healthy adult volunteers. Aliquots with 0.5 ml of washed RBC resuspended in autologous plasma to a hematocrit of 48% and containing 0%, 5%, 10%, 20%, 30% and 40% of Omegaven or Intralipid were prepared and incubated for 30 min at 37 °C. The cells were then fixed with 1% glutaraldehyde and inspected under an inverted brightfield microscope. The extent of echinocytosis was quantified by means of the morphological index (MI), calculated according to the standard protocol.

Results It was found that at concentrations equal to and higher than 20%, Omegaven produced significantly higher RBC morphological index (MI) than Intralipid: mean MI at 20% for Intralipid was 0.61±0.24 and for Omegaven 1.12±0.43 (p<0.01), whereas at 40% MI was 1.47±0.37 and 2.48±0.66 for Intralipid and Omegaven, respectively (p<0.01).

Conclusions At concentrations over 20% Omegaven is more likely to cause echinocytosis than Intralipid. The higher concentrations may occur in vivo if Omegaven is given separately from other parenteral nutrition fluids (two-in one).