Chronic hypoxaemia and secondary polycythaemia in adult cystic fibrosis

Secondary Polycythaemia is rarely found in the adult cystic fibrosis (CF) population despite chronic or recurrent severe hypoxaemia. Previously, this may have been accepted by the fact that CF patients did not live long enough to develop this feature. However with modern therapeutic measures, life expectancy has improved in this group, so much so that one would expect to encounter polycythaemia more frequently. It was theorised that the reason for the absence of this finding is that the CF population is often nutritionally deficient and/or a sufferer of recurrent respiratory tract infections giving rise to either a vitamin deficiency anaemia or an "anaemia of chronic disorders". A normal range haemoglobin in this group, therefore, might represent polycythaemia compensating anaemia. The aim of this study was to investigate the extent of the secondary polycythaemic response to chronic hypoxaemia in a CF group (n=15, mean age 24.6 yrs, M:F=3:2) and to compare this to the response of a group hypoxaemic secondary to a Right-Left reversed cardiac shunt (i.e. Eisenmenger's Syndrome, ES, n=5, mean age 34.6 yrs, M:F= 1:4) and a group of healthy controls (n=17, mean age 14 yrs, M:F=1:2.4). In addition it was wished to determine if the lack of an eiythropoietic response to hypoxaemia in the CF group could be explained by either inadequate vitamin stores or the frequency of respiratory infections (RTIs). Each volunteer had their FBC, haemetinics, erythropoietin level and RCV checked as well their O2 saturations monitored both at rest and during exercise. Finally, the frequency of RTIs were recorded. As expected, the mean Hb and HCT were significantly higher (p<0.05) in the ES group. While there was no significant difference in O2 saturation at rest, this was significantly lower in the ES group (p<0.05) during exercise. The ES group also demonstrated deficiency of B12, Folate, Ferritin and Iron. Higher B12, Folate and Ferritin levels in the CF group reflected an excellent nutritional status. In addition, 86% of our CF population had mild disease only. It was concluded therefore that secondary polycythaemia was not being masked in the CF group studied, either by nutritional deficiency or anaemia of chronic disease.