HAEMATOCRIT REDUCTION CONCOMITANT WITH ACUTE PHASE REACTANT RISE

The study aimed to investigate haematocrit variation as acute phase reactants rise in myocardial infarction.

Serial measurements of haematocrit were undertaken in a cohort (N = 60) of patients over periods ranging from 6 to 28 days. Concurrent measurements of plasma fibrinogen were made by the method of Clauss. Patients with clinical or radiological evidence of heart failure were excluded as were patients with history or evidence of bleeding for any cause.

Results showed a small initial transient rise in haematocrit above baseline of 3% within the first 12 hours post-infarction, followed by a mean decrease below baseline of the order of −16%. The decrease was maintained at the time of discharge from hospital (mean 9.5 days) at a level of −11%. In the single case where serial haematocrits were measured up to 28 days, haematocrit was still reduced by −12%. The maximum individual percentage decrease measured in any patient exceeded −30% and occurred at 3 days post-infarct. The decrease parallelled the rise in plasma fibrinogen but apart from the early post−infarct period, the correlation was poor because of the rise in other acute phase reactants subsequently.

A postulated mechanism for the fall in haematocrit is that it reflects haemodilution. This is in part a physiological compensatory mechanism for the increasein colloid osmotic pressure that is attendant on the increase in acute phase reactants due to myocardial tissue destruction. The blood loss due to serial diagnostic phlebotomies cannot explain the magnitude of the decrease.