THE RELATIONSHIP BETWEEN GLOMERULAR FILTRATION RATE MEASURED AS IOHEXOL-CLEARANCE AND AMBULATORY BLOOD PRESSURE IN THE GENERAL POPULATION: PP.9.364

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Objective: The relationship between blood pressure (BP) and the kidney is complex, and each may adversely affect the other. It has been hypothesized that slightly reduced glomerular filtration rate (GFR) might be associated with increased BP, but this has not been investigated. In a large cross-sectional study we explored the relationship between an accurate measure of GFR and 24-h ambulatory BP (ABP) in the general population. Design and Methods: In the Renal Iohexol-clearance Survey in Tromsø 6 (RENIS-T6), a representative sample of persons aged 50 to 62 years from the general population were studied. The subjects were recruited from the sixth Tromsø Study. Persons with diabetes, chronic kidney disease or cardiovascular disease were excluded. Office BP, height, body weight, antihypertensive medication, smoking habits, and 24 hour ambulatory BP (ABP) were recorded. GFR was measured as single sample iohexol-clearance. We analyzed the associations between ABP and GFR in multiple linear regression analyses. Non-linear relationships were explored with generalized additive models. All analyses were adjusted for gender, age, height, weight, antihypertensive medication and current smoking. Results: 1593 subjects were studied. 48% had office systolic BP ≥140; diastolic BP ≥90 or used antihypertensives. There were significant non-linear associations between GFR and both day-time, night-time and office diastolic BP (P < 0.05). For night-time diastolic BP, GFR was reduced for measurements >80 mmHg (see figure). For office and day-time diastolic BP, the pattern was similar but the threshold for reduced GFR was 90 mmHg. There was a significant linear association between office diastolic BP and GFR, but this was not found between ambulatory BP and GFR. There were neither linear nor non-linear associations between GFR and office or ambulatory systolic BP.Conclusion: An increase in diastolic ABP was associated with slightly reduced GFR in the middle-aged healthy general population. This may be consistent with the hypothesis of a renal cause of essential hypertension, but can also be explained by renal damage caused by elevated BP.