ASSESSMENT OF CORRELATION BETWEEN 24-HOUR URINARY SODIUM EXCRETION AND 24-HOUR AMBULATORY BLOOD PRESSURE IN HEALTHY SUBJECTS AND CHRONIC KIDNEY DISEASE PATIENTS

Salt intake is linked to pathogenesis of hypertension. Sodium excretion in 24-hour urine indicates the daily salt consumption. We assessed relationship between ambulatory BP and sodium excretion in healthy subjects, CKD patients not on dialysis and on maintenance dialysis independent of age or baseline sodium consumption.

STUDY DESIGN: Observational study. 

STUDY POPULATION: Healthy subjects, CKD patients not on dialysis and maintenance dialysis patients.

STUDY SETTING: Ernakulam Medical Centre, Kochi, Kerala-682028 which is a tertiary care medical college hospital in Kerala. The patients are from Nephrology department. 

STUDY PERIOD: September 2022 to September 2023. 

SAMPLE SIZE: minimum sample size was calculated to be 98. 

CRITERIA 

Inclusion criteria: Group 1: healthy subjects Group 2: chronic kidney disease patients not on dialysis Group 3: maintenance dialysis patients. 

Exclusion criteria: Daily intake of nonsteroidal anti-inflammatory drugs, Regular intake of steroids, Patients on diuretic initiation in the previous one month before taking samples, If the period of urine collection was less than 24 hours, Urinary samples in which estimation of sodium cannot be done properly/ undetermined due to technical reasons, Inadequate ABPM (Number of BP recordings less than 80%), Age < 18years, Mentally incapacitated, Current pregnancy, Actively menstruating women and Patients with any malignancy.

24-hour ambulatory blood pressure of all patients were measured with automated, non-invasive, compact, light-weight, programmable, oscillometric ambulatory blood pressure monitor with LCD display device named ABPM – 05, manufactured by Meditech Ltd. 1184 Budapest, MikszáthKálmánutca 24, Hungary.

URINE SAMPLE COLLECTION AND ANALYSIS

Urine samples were collected over 24-hour period, which included the first urine sample on the next day. Each participant received a 5 Litre plastic container for 24-hour urine collection and a 600 mL plastic mug to collect the voided urine and transfer to the container. All collected urine samples were transported to central laboratory within 30 mins for processing and analysis. Measurement of 24-hour urine sodium was done by Indirect Integrated Multisensor Technology (IMT) by Ion Selective Electrode method.

DATA ANALYSIS STATISTICAL TESTS USED

Categorical and quantitative variables were expressed as frequency (percentage) and mean ± SD respectively. Descriptive statistics such as mean ± SD, Median with Inter Quartile Range, minimum and maximum were used describe regarding 24-hour urine sodium. Karl Pearson correlation was used to find out the relationship of BP with 24- hour urine sodium. Chi-square test was used to find the association between categorical variables. For all statistical interpretations, p< 0.05 was considered the threshold for statistical significance. Statistical analyses were performed by using a statistical software package SPSS, version 20.0.

In our study, there is a positive but not statistically significant correlation between 24-hour urinary sodium and mean SBP in CKD patients not on dialysis. Regarding ABPM in CKD population, there is no correlation of 24-hour blood pressure and 24-hour urinary sodium excretion. Thus, estimation of 24-hour urine sodium excretion cannot predict hypertension in CKD population. However, more studies are required in CKD population to establish these facts.