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J Trop Med Hyg. 1993 Oct;96(5):267-73.

Within-person variation in urinary sodium, potassium and creatinine concentrations, and their relationship to changes in the blood pressure of adult male Gambians.

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Department of Epidemiology and Population Sciences, London School of Hygiene and Tropical Medicine, UK.


Variation in urinary electrolyte and creatinine concentrations was studied in untimed, casual specimens obtained from 65 adult Gambian males over a 15-month period during which up to nine specimens were obtained from each subject. Measurements of blood pressure were made at the times when specimens were collected. The within-person variation in urinary creatinine, sodium and potassium concentrations were all found to be larger than that between persons. Within individual subjects, the sodium concentration tended to be comparatively low, and the potassium concentration high, in specimens in which the creatinine concentration was high. This suggests that the excretion of sodium was reduced at times of relative dehydration while the excretion of potassium may have been unrelated to the urine flow. The data also suggest that changes in the state of hydration were associated with changes in blood pressure since an individual subject's pressure was inversely related to the creatinine concentration. The negative relationship of the sodium:potassium ratio with creatinine concentration casts doubt on the simple use of this ratio as an indicator of dietary intake. After adjusting for creatinine concentration by multiple regression, changes in systolic pressure were shown to be positively correlated with changes in sodium concentration. These observations show the importance of replicating measurements of urinary electrolyte concentrations. The demonstration of complex inter-relationships between blood pressure and urinary concentrations of creatinine, sodium and potassium emphasizes the need for care in the interpretation of findings from causal, untimed urine specimens.

[Indexed for MEDLINE]

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