Use of Spot Urine Samples in Estimation of Daily Sodium Intake in Patients with Chronic Kidney Disease
Noha Abdel Hamid Omran;
Abstract
Sodium intake is an important issue for patients with chronic kidney disease (CKD). These patients are characterized by hypertension, which is thought to be predominantly salt sensitive (Weir and Fink, 2005).
Dietary sodium intake shows great promise as a modifiable risk factor for reducing the risks of cardiovascular disease and CKD progression (Wright and Cavanaugh, 2010).
Although, the estimation of salt intake is essential, there are no easy methods to estimate real salt intake. The two most widely used methods to measure sodium intake are: 24-hour urine sodium excretion measurement and sodium intake estimation by dietary recall.
Alternative methods have emerged as a substitute for the gold standard 24‐hour urinary sodium collection. Different equations have been used to estimate Na intake using spot urine samples. Of special interest are: Tanaka and Kawasaki’s equations which have been used before to estimate 24-hour urine excretion and thus daily salt intake (Kawano et al., 2007).
This study was conducted on 60 CKD patients, none of which is on dialysis, admitted to Internal Medicine Department at Ain Shams University Hospitals. Patients completed 24-hour urine collection and the spot urine sample was examined on the same day that patients completed their 24-hour urine sample collection (coinciding with the second voiding urine of the day before patients had breakfast) and estimation of salt intake by spot urine was done using Tanaka’s formula as well as Kawasaki's formula. The results were compared to the measured urinary sodium in 24-hr urine samples.
Patients were classified according to their creatinine clearance as measured using their 24-hr urine samples. The creatinine clearance ranged from 7.1 ml/min/1.73m2 to 89 ml/min/1.73m2 with median of 42.5 ml/min/1.73m2. Stages of CKD were identified accordingly and patients were categorized into CKD stages ranging from Stage 2 to Stage 5.
20 patients were assorted as stage 2 (33.3%), 20 patients as stage 3 (33.3%), 16 patients as stage 4 (26.7%), and only 4 patients as stage 5 (6.7%). None of the enrolled patients were assorted as CKD stage 1. Their ages ranged from 21 years to 80 years. There was male predominance among our enrolled patients where male : female ratio was 4 : 1. 38% of our patients were diabetic and 55% were hypertensive.
As regards the validity of spot urine samples in estimating the 24 hour urinary sodium excretion (and thus daily sodium intake), our results showed a strong positive correlation between the results of 24-hour urinary sodium excretion and those estimated from spot urine samples using Tanaka and Kawasaki’s equations (P<0.001).
This applies to patients of CKD stages 2, 3 and 4 with the relation being stronger in stages 2 and 3. However, for stage 5 CKD, there was no statistically significant relation between the two methods using either equation.
Comparing both Tanaka and Kawasaki’s equations as an accurate method to estimate 24-hour urinary sodium excretion, our study showed that Tanaka’s equation had stronger correlation with measured 24-hour urinary sodium and thus is a more accurate method for estimation of sodium excretion than Kawasaki’s equation in stages 2 and 4 CKD (r=0.968 and r=0.788 compared to r=0.936 and r=0.768 respectively).
However, in stage 3, Kawasaki’s equation was more accurate than Tanaka’s equation (r=0.928 compared to 0.919 respectively). Both of the equations can’t be used to estimate 24-hour Na excretion and thus daily Na intake in patients of stage 5 CKD.
Comparing the measured 24-hour urinary sodium and estimated 24-hour urinary sodium by spot urine samples using Tanaka’s and Kawasaki’s formulae, the correlation was found to be stronger in females (r=0.971, 0.941) than in males (r=0.888, 0.883).
During our study it was observed that the majority of our patients were consuming more salt than the recommended levels (< 5gm NaCl per day for CKD patients according to KDOQI guidelines, 2013), which is likely because it is "hidden" from both their eyes and taste buds. In all stages of CKD, it ranged from 1.350 to 18.430 gm/day with a mean of 7.271 ± 3.387. The mean was greater for patients of CKD stage 2 and 5 where it was 8.259 ± 3.397 and 8.624 ± 0.237 respectively.
As previously stated, 55% of our patients were hypertensive. As regards the relationship between urinary sodium excretion and blood pressure, our study showed no statistically significant relationship between degree of hypertension (as reflected by systolic, diastolic and mean blood pressure readings) and values of measured 24 hour urinary sodium excretion (P=0.144, P=0.075 and P=0.073 for SBP, DBP and MBP respectively).
This was also true for that estimated from the spot urine sample by using Tanaka’s equations. (P=0.076, P=0.074 and P=0.052 for SBP, DBP and MBP respectively). On the contrar
Dietary sodium intake shows great promise as a modifiable risk factor for reducing the risks of cardiovascular disease and CKD progression (Wright and Cavanaugh, 2010).
Although, the estimation of salt intake is essential, there are no easy methods to estimate real salt intake. The two most widely used methods to measure sodium intake are: 24-hour urine sodium excretion measurement and sodium intake estimation by dietary recall.
Alternative methods have emerged as a substitute for the gold standard 24‐hour urinary sodium collection. Different equations have been used to estimate Na intake using spot urine samples. Of special interest are: Tanaka and Kawasaki’s equations which have been used before to estimate 24-hour urine excretion and thus daily salt intake (Kawano et al., 2007).
This study was conducted on 60 CKD patients, none of which is on dialysis, admitted to Internal Medicine Department at Ain Shams University Hospitals. Patients completed 24-hour urine collection and the spot urine sample was examined on the same day that patients completed their 24-hour urine sample collection (coinciding with the second voiding urine of the day before patients had breakfast) and estimation of salt intake by spot urine was done using Tanaka’s formula as well as Kawasaki's formula. The results were compared to the measured urinary sodium in 24-hr urine samples.
Patients were classified according to their creatinine clearance as measured using their 24-hr urine samples. The creatinine clearance ranged from 7.1 ml/min/1.73m2 to 89 ml/min/1.73m2 with median of 42.5 ml/min/1.73m2. Stages of CKD were identified accordingly and patients were categorized into CKD stages ranging from Stage 2 to Stage 5.
20 patients were assorted as stage 2 (33.3%), 20 patients as stage 3 (33.3%), 16 patients as stage 4 (26.7%), and only 4 patients as stage 5 (6.7%). None of the enrolled patients were assorted as CKD stage 1. Their ages ranged from 21 years to 80 years. There was male predominance among our enrolled patients where male : female ratio was 4 : 1. 38% of our patients were diabetic and 55% were hypertensive.
As regards the validity of spot urine samples in estimating the 24 hour urinary sodium excretion (and thus daily sodium intake), our results showed a strong positive correlation between the results of 24-hour urinary sodium excretion and those estimated from spot urine samples using Tanaka and Kawasaki’s equations (P<0.001).
This applies to patients of CKD stages 2, 3 and 4 with the relation being stronger in stages 2 and 3. However, for stage 5 CKD, there was no statistically significant relation between the two methods using either equation.
Comparing both Tanaka and Kawasaki’s equations as an accurate method to estimate 24-hour urinary sodium excretion, our study showed that Tanaka’s equation had stronger correlation with measured 24-hour urinary sodium and thus is a more accurate method for estimation of sodium excretion than Kawasaki’s equation in stages 2 and 4 CKD (r=0.968 and r=0.788 compared to r=0.936 and r=0.768 respectively).
However, in stage 3, Kawasaki’s equation was more accurate than Tanaka’s equation (r=0.928 compared to 0.919 respectively). Both of the equations can’t be used to estimate 24-hour Na excretion and thus daily Na intake in patients of stage 5 CKD.
Comparing the measured 24-hour urinary sodium and estimated 24-hour urinary sodium by spot urine samples using Tanaka’s and Kawasaki’s formulae, the correlation was found to be stronger in females (r=0.971, 0.941) than in males (r=0.888, 0.883).
During our study it was observed that the majority of our patients were consuming more salt than the recommended levels (< 5gm NaCl per day for CKD patients according to KDOQI guidelines, 2013), which is likely because it is "hidden" from both their eyes and taste buds. In all stages of CKD, it ranged from 1.350 to 18.430 gm/day with a mean of 7.271 ± 3.387. The mean was greater for patients of CKD stage 2 and 5 where it was 8.259 ± 3.397 and 8.624 ± 0.237 respectively.
As previously stated, 55% of our patients were hypertensive. As regards the relationship between urinary sodium excretion and blood pressure, our study showed no statistically significant relationship between degree of hypertension (as reflected by systolic, diastolic and mean blood pressure readings) and values of measured 24 hour urinary sodium excretion (P=0.144, P=0.075 and P=0.073 for SBP, DBP and MBP respectively).
This was also true for that estimated from the spot urine sample by using Tanaka’s equations. (P=0.076, P=0.074 and P=0.052 for SBP, DBP and MBP respectively). On the contrar
Other data
| Title | Use of Spot Urine Samples in Estimation of Daily Sodium Intake in Patients with Chronic Kidney Disease | Other Titles | استخدام عينة البول العشوائية لقياس نسبةاستهلاكالصوديوم في مرضى القصور المزمن بالكلى | Authors | Noha Abdel Hamid Omran | Issue Date | 2014 |
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