Effects of bilirubin and phototherapy on osmotic fragility and haematoporphyrin-induced photohaemolysis of normal erythrocytes and spherocytes.

AIM: To study the effects of phototherapy on erythrocyte haemolysis in vitro and to determine possible differences in sensitivity to phototherapy between normal erythrocytes and spherocytes.

METHODS

Erythrocytes from four normal healthy donors and two donors with hereditary spherocytosis were treated with bilirubin (160 microM) in the presence of human serum albumin in the molecular ratio bilirubin/albumin 0.8. Treated cells were maintained either in the dark or in blue light (450 nm, 8 mW/cm2, 30 min). The experimental light dose was comparable to 2 h of clinical phototherapy. The osmotic fragility of the treated cells was measured by scoring haemolysis in hypo-osmolar solutions (0.10-0.90% NaCl). The sensitivity to photohaemolysis of cells pre-treated with bilirubin (BR) and/or phototherapy was tested by exposing the cell suspensions to haematoporphyrin and UVA radiation. The delayed (18 h) photohaemolysis was measured by spectrophotometry.

RESULTS

Osmotic fragility, expressed as percentage haemolysis, of normal erythrocytes was more than doubled in the presence of BR combined with phototherapy (n = 6, p < 0.05). In contrast, osmotic fragility of spherocytes was unaffected by either treatment (n = 8, p < 0.05). Increased photohaemolysis was seen in spherocytes treated with BR (n = 13, p < 0.05), phototherapy (n = 13, p < 0.05) and a combination of the two agents (n = 13, p < 0.05) compared with spherocytes without BR in the dark (n = 6).

CONCLUSION

Bilirubin may make the plasma membrane of normal erythrocytes more fragile. Newborns with hereditary spherocytosis may be sensitive to phototherapy.