Estimation of glomerular filtration rate: does haemoglobin discriminate between ageing and true CKD?

AIM: The aim of this study was to analyse the association between chronic kidney disease (CKD) defined by an estimated glomerular filtration rate (eGFR) <60 ml/min/ 1.73 m(2) and anaemia in older people.

BACKGROUND: Guidelines focus on early identification and management of CKD to prevent CKD progression and cardiovascular disease. However, the significance of CKD classification using eGFR in older people is unclear.

METHODS: Serum creatinine and haemoglobin from individuals attending non-nephrology outpatient clinics were extracted from the state pathology provider over a 4-month period. The associations between eGFR, gender, age and haemoglobin were explored.

RESULTS: Serum creatinine in 9853 individual patients aged > or =15 years was available for analysis. Haemoglobin was simultaneously available in 8752 (88.8%) subjects. There was a negative relationship between age and median eGFR, and the slope of the regression line was -0.68 ml/min/year for males and -0.74 ml/min/year for females. Over 35% of individuals > or =65 years were classified as having CKD stage > or =3. Odds ratios for haemoglobin <100 g/l for an eGFR <15, 15-29 and 30-59 versus reference GFR > or =60 ml/ min/1.73 m(2) in subjects 25-44 years were 34.2 (30.7-37.7), 23.4 (20.2-26.6) and 7.2 (5.3-9.1), respectively. In comparison, these were 8.9 (6.7-11.1), 5.6 (4.9-7.3) and 1.6 (1.1-2.1), respectively, in subjects > or =65 years. In subjects > or =65 years, odds ratios for haemoglobin <100 g/l for an eGFR 30-44 and 45-59 ml/min/1.73 m(2) versus reference GFR > or =60 ml/min/1.73 m(2) were 1.9 (1.3-2.5) and 1.2 (0.7-1.7), respectively.

CONCLUSIONS: An eGFR <60 ml/min/1.73 m(2) is very common in older people. Only an eGFR <45 ml/min/1.73 m(2) identified a smaller sub-group of older people with an increased prevalence of significant anaemia suggesting a clinically relevant disease. The benefits of identifying older people with an eGFR > or =45 ml/min/1.73 m(2) need to be determined.