LOW PLASMA HEPARIN-COFACTOR-II LEVELS IN THALASSEMIA SYNDROMES ARE CORRECTED BY CHRONIC BLOOD-TRANSFUSION

Low plasma heparin cofactor II (HCII) levels are associated with a thr ombotic tendency, and we have previously shown these to be decreased i n a variety of haemolytic conditions, The risk of thrombosis is recogn ized to be increased in both thalassaemia major (TM) and intermedia (T I), although the exact mechanisms are poorly understood. HCII levels h ave therefore been compared in 20 untransfused patients with TI and 20 regularly. transfused TM patients to determine the influence of trans fusion on HCII. Additionally, untransfused TI patients have been comme nced on regular red cell transfusion and the effects on correction of low HCII levels investigated. HCII levels were significantly lower in the untransfused TI patients (mean 0.56 +/- 0.06 U/ml) compared to TM patients (mean 0.85 +/- 0.1 U/ml; P < 0.001). Levels in TI were signif icantly less than in healthy age-matched controls (P < 0.001) and corr elated with Hb values (r = 0.8), whereas levels in TM were at the lowe r end of the normal range. ATIII values were within the normal referen ce range in both TI and TM, and HCII antigen showed a parallel reducti on to HCII. activity, indicating that reduction in HCII is not a conse quence of increased thrombin consumption. Three patients with TI were commenced prospectively on hypertransfusion programmes which resulted in a slow normalization of their levels taking 2-3 months. These findi ngs support a hypothesis that the low HCII levels are related to incre ased red cell turnover and can be normalized once this turnover has be en suppressed by hypertransfusion, The thrombotic risk to patients wit h low HCII levels in the presence of haemolysis might in principle be decreased by such transfusion regimes.