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

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.

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.

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.

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.

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.