The effect of blood urea nitrogen/creatinine and blood urea nitrogen/albumin ratios on the prognosis and mortality of patients in the palliative care service

Introduction

Serum creatinine, blood urea nitrogen (BUN), and electrolyte levels are the most used tests to evaluate kidney functions, and the BUN level is also used to evaluate hypovolaemia as well as kidney functions [1–3]. Causes such as excessive protein intake, amino acid infusion, accelerated catabolism, acute illness, some antibiotics such as tetracycline, or steroid use can increase BUN without kidney disease [1]. Apart from these, BUN level has been shown to be higher in patients with pneumonia, chronic obstructive pulmonary disease, pancreatitis, acute myocardial infarction, heart failure, sepsis, and geriatric mortality [3–9].
The ratio of BUN to creatinine (BCR) is frequently used to determine the level of dehydration [3]. The BCR is normally 10/1, and greater than 10 may be a sign of decreased extracellular fluid volume. Its proportional increase indicates renal failure [1]. BCR is also used for the prognosis of many diseases such as stroke, gastrointestinal bleeding, heart failure, and hip fracture [10–14].
Albumin is a protein and a negative acute phase reactant, and it directly or indirectly reflects conditions such as nutrition and dehydration [15–19]. Albumin levels in patients with pneumonia, acute coronary syndrome, and pancreatitis are low; severe acute malnutrition and hypoalbuminaemia are associated with high mortality in patients with various diseases [20–23] . Studies have been conducted to estimate the mortality rate with the BUN/albumin ratio (BAR) in geriatric patients and patients with pneumonia, and it has been reported that the predictive power of BAR for mortality is higher than that of BUN and albumin in these studies [3, 24]. BCR and BAR parameters, which are used frequently in routine blood tests, have recently been associated with the severity and prognosis of chronic diseases [3, 10–14, 24–26].
In our study, we aimed to evaluate the effect of BCR and BAR rates on prognosis and mortality in patients hospitalized in the palliative service with a variety of comorbid diseases.

Material and methods

Patients hospitalized in the palliative service of the local University Training and Research Hospital Family Medicine Department between May 2019 and May 2021 were included in the cross-sectional study. Sociodemographic data such as age, gender, chronic diseases, discharge status, length of stay, blood parameters such as BUN, creatinine, albumin, C-reactive protein (CRP), and haemogram parameters of the patients in the palliative service were recorded retrospectively from the patients’ files and the hospital automation system. BCR was calculated by dividing the serum BUN value by the serum creatinine value, and BAR was calculated by dividing the serum BUN value by the serum albumin value.

Statistical analysis

SPSS package program version 22.0 was used in the statistical analysis of the obtained data. Descriptive statistics were expressed as numbers, percentages, and mean ± standard deviation. In the comparisons between groups, the t-test was used for normally distributed data, and the Wilcoxon signed rank test was used for non-parametric data by looking at the distribution of the data. Categorical data were compared with the 2 test. Pearson correlation test was used for correlation analysis. The significance level was accepted as p < 0.05.

Ethics committee approval

Ethical approval was taken from the University Clinical Research Ethics Committee for this study (Approval letter number: 2021/578, Date of approval: 02/06/2021).

Results

In total, 209 patients who were hospitalized in the palliative care service between May 2019 and May 2021 were included in the study. 57.4% of the patients were male, 44.9% were ≥ 81 years old, and 89.0% were married. Concomitant chronic neurological disease was present in 71.3% of the patients, and oral intake disorder was the reason for hospitalization in the palliative care service in 61.7%. Hospitalization of 53.6% of the patients was done in the family medicine clinic. The average length of stay in the service was 22.4 ±22.1 days. While 78.0% of the patients in the palliative service were discharged alive, 22.0% died (Table 1).
When the blood parameters of the patients who were discharged alive from the palliative service and those who died were compared, there was no difference between the haemoglobin, leukocyte, lymphocyte, platelet, mean platelet volume, or creatinine values, whereas CRP (p = 0.015), BUN (p < 0.001), BCR (p < 0.001), and BAR (p = 0.001) values were high and albumin (p = 0.008) values were low in the patients who died (Table 2).
When the BCR and BAR values of the patients were compared according to their chronic diseases and hospitalization indications, it was observed that the BCR values were statistically significantly higher in those with diabetes mellitus (DM) compared to those without. BCR (p = 0.013) and BAR (p = 0.035) values were found to be statistically significantly higher in patients with cardiovascular system (CVS) disease compared to those without CVS disease (Table 3).
A positive correlation was found between BCR and BAR levels in patients in the palliative service (r = 0.316, p  0.001). It was determined that as the BAR and BCR levels increased, the length of stay in the service, BUN, creatinine, and CRP levels also increased, and the albumin levels decreased as the BAR and BCR levels increased (Table 4).

Discussion

In our study we found a positive correlation between BCR and BAR levels in patients in the palliative service. As their BAR and BCR levels increased, the length of stay in the service, BUN, creatinine, and CRP levels increased but albumin levels decreased, and the BUN, BCR, and BAR levels of patients who died in the palliative service were higher and the albumin levels were lower compared to those who were discharged alive.
BCR and BAR parameters have been associated with the severity and prognosis of chronic diseases in many recent studies [27–30].
It has been reported that the combined use of the BUN/creatinine ratio is more beneficial than the use of both tests alone in differentiating renal azotaemia from prerenal and postrenal azotaemia [31]. BCR increases in prerenal azotaemia such as heart failure, dehydration, blood loss, and shock, and obstructive uropathies such as kidney stones, benign prostatic hypertrophy, and postrenal azotaemia. It decreases in chronic renal failure, long-term dialysis applications, low protein intake, insufficient urea synthesis due to severe liver failure, in cases where urea levels decrease, in conditions that increase muscle breakdown and therefore creatinine synthesis occurs, such as rhabdomyolysis, and in the syndrome of inappropriate antidiuretic hormone secretion that increases urea secretion [31, 32].
Matsue et al. found in their study, comparing BCR levels in patients with acute heart failure to those in the general population, that higher than normal range of BCR is associated with poor prognosis and high mortality, independently of both BUN and creatinine, and that this provides additional prognostic information on pre-existing prognostic factors including BCR, creatinine, and BUN [30].
In the study by Rachoin et al., it was reported that the prevalence of DM, CV disease, and chronic obstructive pulmonary disease is higher in critically ill patients in the intensive care unit, and that there is a correlation between various underlying chronic conditions and high levels of BCR (> 20). It was found that the use of vasopressors and mechanical ventilation was more common in patients with BCR > 20, and these patients had higher mean BUN when admitted to the intensive care unit. In the same study, a significant correlation was shown between BUN and APACHE II score [27]. Similarly, in our study, when the BCR and BAR values of the patients in the palliative service were compared according to their chronic disease, it was found that the BCR value was significantly higher in all patients with a BCR > 20 than in those with DM, those with CVS disease, and those without CVS.
In a study by Feinfeld et al. evaluating BCR in intensive care patients, the mortality rate was found to be 58% in the critically ill group with very high BUN (mean BCR 36) values, high protein catabolism, and low muscle mass [33]. In the study of Rachoin et al., BCR > 20 in critically ill patients in the intensive care unit was associated with increased mortality rates [27]. In our study, the mean BCR values ​​of the entire study group were high (BCR: 45.52), and the mean BCR was found to be significantly higher in the deceased (BCR: 63.55) than in the survivors (BCR: 40.93).
In our study, a positive correlation was found between BAR, length of hospital stay, and mortality. In a retrospective multicentre study by Akyil et al., conducted by P.P. in Turkey with patients diagnosed with community-acquired pneumonia, short-term mortality was found to be 9.2% in 785 patients, and it was reported that high BAR rates were associated with 30-day mortality [28].
In the study of Dundar et al., the risk of in-hospital mortality was found to be higher in elderly patients with a BUN level > 23 mg/dl, albumin level < 3.5 g/dl, and BAR > 6.25 mg/g in the emergency department. In addition, it was reported that BAR is a superior and independent predictor of in-hospital mortality compared to BUN, albumin, creatinine levels, and eGFR in elderly patients [3].
Again, Bae et al. reported that BAR is an important predictor of in-hospital mortality and intensive care unit admission in their study comparing inferior vena cava diameter ratio, BCR, and BAR for risk estimation in emergency room patients [10].
Küçükceran et al. studied the role of BAR in predicting mortality in COVID-19 patients in the emergency department and reported that BAR levels have a reliable predictive value of in-hospital mortality, and that BAR is a more reliable predictor than BUN and albumin levels [29]. Similarly, in recent studies, it has been reported that BAR is an important indicator in the evaluation of mortality in many diseases such as pneumonia and gastrointestinal bleeding [24–26].
The strength of our study is that no study examining BAR or BCR rates in palliative care patients was found in the current literature. The limitation of our study is that it is retrospective.

Conclusions

In this study, which aimed to evaluate the effect of BCR and BAR ratios on prognosis and mortality in patients in the palliative service, it was determined that there was a positive and significant correlation between BCR, and BAR and length of hospital stay and mortality. BCR and BAR, which are thought to be associated with dehydration and malnutrition, are useful and simple parameters that can also be used to predict hospital stay and mortality.
The authors declare no conflict of interest.

References