Glomerular filtration rate and comorbidity factors in elderly hospitalizations

Abstract

BACKGROUND

With an increase in the elderly population, the frequency of hospitalizations in recent years has also risen at a rapid pace. This, in turn, has resulted in poor outcomes and costly treatments. Hospitalization rates increase in elderly patients due to a decline in glomerular filtration rate (GFR).

AIM

To investigate the connection between GFR and comorbidity and reasons for hospitalization in elderly patients.

METHODS

We analyzed patients aged 75 years and over who were admitted to the internal medicine clinic of a tertiary hospital in Eskisehir. At admission, we calculated GFR values using the Modification of Diet in Renal Disease study formula and classified them into six categories: G1, G2, G3a, G3b, G4, and G5. We analyzed associations with hospitalization diagnoses and comorbidity factors.

RESULTS

The average age of the patients was 80.8 years (± 4.5 years). GFR was 57.287 ± 29.5 mL/kg/1.73 m² in women and 61.3 ± 31.5 mL/kg/1.73 m² in men (P = 0.106). Most patients were admitted to the hospital at G2 stage (32.8%). The main reasons for hospitalization were anemia (34.4% and 28.6%) and malnutrition (20.9% and 20.8%) in women and men, respectively (P = 0.078). The most frequent comorbidity leading to hospitalization was arterial hypertension (n = 168, 28%), followed by diabetes (n = 166, 27.7%) (P = 0.001).

CONCLUSION

When evaluating geriatric patients, low GFR alone does not provide sufficient information. Patients’ comorbid factors should also be taken into account. There is no association between low GFR during hospitalization and hospitalization-related diagnoses. Knowing the GFR value before hospitalization will be more informative in such studies.

Key Words: Aging; Glomerular filtration rate; Hospitalization; Comorbidity; Elderly hospitalizations

Core Tip: The process of aging is a natural phenomenon, and the quality of life is of paramount importance during this period. The objective of this study was to examine the relationship between renal filtration rate and health outcomes, as well as the incidence of hospitalization, in elderly patients. The analysis was conducted in patients aged 75 years and older who were admitted to the internal medicine clinic of a tertiary care hospital in Eskisehir. At the time of admission, renal filtration rates were calculated using the Modification of Diet in Renal Disease formula and classified into six categories. Associations with health problems during the course of hospitalization were analyzed.

INTRODUCTION

As individuals age, a noticeable decrease in glomerular filtration rate (GFR) occurs, which reflects the loss of renal function. It becomes difficult to differentiate between GFR loss due to healthy aging and a decline caused by renal diseases[1]. As a result, using GFR measurements to determine prognosis in older adults becomes problematic. As a consequence of the anticipated reduction in GFR of 1 mL/min/1.73 m² per year, healthy older adults exhibit a reduced estimated GFR in comparison to younger adults[2-4]. Research showed that 50% of people aged over 70 years had a measured or estimated GFR lower than 60 mL/min/1.73 m²[5]. Furthermore, studies indicate a link between poor health outcomes and reduced GFR in patients with comorbidities[6]. A population-based study recently reported the association between GFR loss and mortality[7]. Multiple studies conducted in different countries with large patient populations have concluded that GFR loss raises the risk of mortality[8-10]. The appropriate management of renal failure is crucial in elderly patients, given its increasing prevalence, poor outcomes, and high treatment costs that contribute to a global public health issue. In particular, patients aged 75 years and older were preferred to more clearly assess the lasting effects of GFR decline. Our study aimed to explore the correlation between hospitalization diagnoses, comorbidity and GFR.

MATERIALS AND METHODS

Participants aged 75 years and older who were regularly examined in internal medicine outpatient clinics were included in the study. Data from 600 patients were analyzed retrospectively. Individuals with indications for intensive care unit hospitalization and emergency hemodialysis were excluded. These were patients with an acutely decreased GFR and a clinical picture with high mortality. Only patients with stable vital signs who were hospitalized in internal medicine clinics were included in the study. Age, gender, comorbidities, GFR, certain laboratory characteristics, and hospitalization diagnosis were recorded. BMI was calculated according to the World Health Organization guidelines[11]. Hospitalization GFR values were calculated using the Modification of Diet in Renal Disease (MDRD) study formula[12]. The MDRD formula is the preferred method for calculating GFR because it is widely accepted by physicians in clinical practice and has a large body of data from studies. Staging was based on six GFR categories: G1, G2, G3a, G3b, G4, and G5[13]. GFR groups based on mL/min/1.73 m² were as follows: G1 with GFR ≥ 90, G2 with GFR 60-89, G3a with GFR 45-59, G3b with GFR 30-44, G4 with GFR 15-29, and G5 with GFR < 15. The use of retrospective data analysis limited our study.

Mean and standard deviation were used to express continuous variables, and categorical variables were expressed as percentages. The obtained results were expressed using standard average and deviation. The Kolmogorov-Smirnov test was used to assess normality. The Pearson χ² test was used to compare categorical parameters. The comparison of different numerical parameters was analyzed using an independent samples test. To evaluate and assess the differences between groups Fisher’s exact test and analysis of variance were employed. Post-hoc analyses were conducted using Tukey’s and Tamhane’s methods. A P value of less than 0.05 was considered statistically significant. The analysis was carried out using IBM SPSS Statistics 25.0 software.

RESULTS

We examined 600 patients admitted to the internal medicine ward. Among them, 231 (38.5%) patients were male, and 369 (61.5%) were female. The difference between the numbers of male and female patients was not statistically significant (P = 0.130). The average age of all patients was 80.8 (± 4.5) years. The GFR was 57.287 ± 29.5 mL/kg/1.73 m² in women and 61.3 ± 31.5 mL/kg/1.73 m² in men (P = 0.106). The GFR values of the patients during hospitalization were calculated using the MDRD formula and analyzed in six groups. The most common hospitalization stage for patients was G2 (32.8%). A total of 147 (24.5%) patients did not have any comorbidities. Arterial hypertension (n = 168, 28%) was the most frequent comorbidity, followed by diabetes (n = 166, 27.7%). Table 1 shows the characteristics of patients according to GFR groups.

Table 1 Patients characteristics, mean ± SD.

Variable	G1	G2	G3a	G3b	G4	G5	P value
Age of males, years	81.7 ± 5.8	80.6 ± 3.9	81.7 ± 5.8	80.6 ± 3.9	82.6 ± 5.0	82.5 ± 4.7	0.106
Age of females, years	79.9 ± 3.5	80.1 ± 3.9	79.9 ± 3.5	80.1 ± 3.9	81.8 ± 4.8	81.8 ± 3.9
Serum urea nitrogen (mg/dL)	19 ± 8	21 ± 7	28 ± 13	39 ± 20	63 ± 28	87 ± 25	0.01
Creatinine (mg/dL)	0.64 ± 0.1	0.87 ± 0.1	1.18 ± 0.17	1.56 ± 0.2	2.42 ± 0.55	4.88 ± 2.09	0.01
GFR (mL/kg/1.73 m2)	109.1 ± 18	72.4 ± 8.1	52.2 ± 4.2	37.8 ± 4.6	23.1 ± 4.4	11.1 ± 3.2	0.01
Hemoglobin (g/dL)	11 ± 3	11 ± 3	11 ± 3	11 ± 2	11 ± 2	11 ± 2	0.01
Hematocrit (g/dL)	33 ± 9	35 ± 8	34 ± 9	33 ± 7	34 ± 8	34 ± 7	0.01
No comorbidity, n (%)	111 ± 24, 24 (16.3)	73.7 ± 9, 64 (43.5)	52.5 ± 4.6, 29 (19.7)	38.8 ± 4.1, 21 (14.3)	23.4 ± 3.3, 7 (4.8)	12.5 ± 2.1, 2 (1.4)	0.010
MDS, n (%)	136 ± 36, 4 (16)	69 ± 6.7, 12 (48)	48.1 ± 3.4, 3 (12)	35.4 ± 4.1, 4 (16)	20.7 ± 6, 12 (8)	0	0.396
Diabetes, n (%)	105 ± 11.5, 21 (12.7)	72.6 ± 7.7, 43 (25.9)	51.8 ± 3.6, 27 (16.3)	37.5 ± 4.6, 42 (25.3)	23.2 ± 4.4, 18 (10.8%)	11 ± 3.4, 15 (9%)	0.020
Alzheimer’s, n (%)	112 ± 12, 11 (25)	74.6 ± 7.8, 9 (20.5)	50.5 ± 3.3, 6 (13.6)	35.7 ± 5, 6 (13.6)	24.9 ± 3.8, 9 (20.5%)	8.1 ± 4, 3 (6.8%)	0.078
CAD, n (%)	103 ± 0.6, 2 (9.5)	70.5 ± 10, 552.2 ± 8 (31)	52.2 ± 5.5, 2 (9.5)	35.3 ± 3, 3 (14.3)	24.5 ± 6.7, 3 (14.3)	11.5 ± 1.3, 3 (14.3)	0.690
CVO, n (%)	95.8 ± 6.4, 2 (20)	69.6, 1 (10)	0	36.6 ± 8.9, 2 (20)	16.9, 1 (10)	12 ± 2.8, 4 (40)	0.046
Arterial hypertension, n (%)	107 ± 15, 27 (16)	71 ± 7.4, 57 (33.9)	52.6 ± 4.5, 24 (14.3)	39.1 ± 4.5, 24 (14.3)	22.2 ± 4.5, 19 (11.3)	11.3 ± 3.5, 17 (10.1)	0.341
COPD, n (%)	111.6, 1 (12.5)	74.9 ± 17, 2 (25)	54 ± 2, 43 (37.5)	0	21.9 ± 5.2, 2 (25)	0	0.279
Cancer, n (%)	0	81.4, 1 (9,1)	56.9 ± 2.1, 2 (18.2)	37.2 ± 5.3, 6 (54.5)	28.5, 1 (9.1)	10.2, 1 (9.1)	0.034

GFR: Glomerular filtration rate; MDS: Myelodysplastic syndrome; CAD: Coronary artery disease; CVO: Cerebrovascular disease; COPD: Chronic obstructive pulmonary disease.

Table 2 shows the analysis of patient diagnoses upon admission to the clinic according to GFR groups. There was no significant difference in hospitalization diagnoses between male and female patients (P = 0.308). The primary reasons for hospitalization were anemia (34.4% and 28.6%) and malnutrition (20.9% and 20.8%) for women and men, respectively. Men had higher rates of hospitalization caused by pneumonia (5.2%) and acute renal failure (13.4%). Women had a higher incidence of urinary infections (8.4%). There was no statistically significant difference in comorbidities observed between men and women (P = 0.078). The highest number of hospitalizations was observed among patients without comorbidities and those with diabetes and arterial hypertension. Table 3 illustrates the relationship between comorbidities and indications for hospitalization. The most common indications for hospitalization among patients without comorbidities were G2 stage (43.5%), anemia (46.9%), and malnutrition (25.2%). Patients with Alzheimer’s disease were admitted to hospitals in G1 stage (40%), the most common reason being malnutrition (40.9%). Patients with cerebrovascular occlusion were admitted to hospitals in G5 stage (40%), with acute renal failure (40%) being the most frequent cause, followed by urinary infection (30%). Patients with chronic obstructive pulmonary disease were hospitalized with anemia (50%) in G3a stage (37.5%). Patients with cancer were hospitalized with anemia (45.5%) in G3b stage (54.5%).

Table 2 Causes of hospitalization by glomerular filtration rate stage, mean ± SD (%).

Reason for hospitalization	G1	G2	G3a	G3b	G4	G5	P value1
Anemia	110.9 ± 18.6 (35.9)	71.4 ± 7.9 (33.0)	51.5 ± 4.2 (40.6)	37.6 ± 4.5 (34.3)	22.9 ± 5.5 (21.0)	10.9 ± 2.9 (11.1)	0.030
Hyperglycemia	100.6 ± 8.1 (7.6)	73 ± 6.8 (13.7)	52.2 ± 3.8 (21.9)	38 ± 5 (18.5)	24.9 ± 4.6 (14.5)	0	0.331
Pneumonia	104.4 ± 8.3 (4.3)	78.1 ± 7.7 (4.6)	55.5 ± 3.8 (2.1)	40.2 ± 1.5 (2.8)	27 (1.6)	0	0.541
Urine infection	108.1 ± 29.4 (4.3)	73.5 ± 8.5 (11.7)	53.2 ± 5.6 (7.3)	37.9 ± 5.2 (8.3)	24.6 ± 3.7 (4.8)	12.5 (2.2)	0.130
Hyponatremia	104.4 ± 10.7 (9.8)	73.7 ± 9.7 (3.0)	52.8 ± 4.6 (6.3)	38.8 ± 3.9 (5.6)	25.3 ± 0.9 (6.5)	13.6 (2.2)	0.233
Malnutrition	109.5 ± 22.2 (27.2)	72.3 ± 8.6 (21.8)	53.4 ± 3 (11.3)	38.7 ± 4.2 (20.3)	25.7 ± 2.4 (13.5)	0	0.000
Acute renal failure	121 (1.1)	0	0	35.4 ± 5.4 (8.3)	20.1 ± 3.4 (32.3)	10.9 ± 3.5 (77.8)	0.000
Hypernatremia	105.3 (1.1)	0	0	0	27 (1.6)	11.7 ± 0.1 (4.4)	0.019
Hypoglycemia	110 (1.1)	74.3 ± 11 (3.0)	48.5 ± 3.9 (2.1)	34 (0.9)	25.4 ± 3.3 (3.2)	0	0.620
Polycythemia	91.4 (1.1)	69 ± 3.1 (2.5)	53.4 ± 7.9 (2.1)	0	0	0	0.354
Gastroenteritis	140.9 ± 5.9 (2.2)	71 (0.5)	53.1 ± 6.1 (3.1)	35.5 ± 3.5 (1.9)	4.5 ± 12 (3.2)	12 (2.2)	0.611

¹Fisher’s exact test and Pearson χ²-tests.

Table 3 Reason for hospitalization and comorbidity factors relationship, n (%).

Reason for hospitalization	None	MDS	Diabetes	Alzheimer’s	CAD	CVO	Arterial hypertension	COPD	Cancer	P value1
Anemia	69 (35.8)	24 (12.4)	24 (12.4)	14 (7.3)	7 (3.6)	2 (1.0)	44 (22.8)	4 (2.1)	5 (2.6)	0.01
Hyperglycemia	2 (2.4)	1 (1.2)	78 (92.9)	0	0	0	3 (3.6)	0	0	0.506
Pneumonia	6 (31.6)	0	7 (36.8)	0	0	0	5 (26.3)	1 (5.3)	0	0.545
Urine infection	18 (38.3)	0	4 (8.5)	5 (10.6)	4 (8.5)	3 (6.4)	13 (27.7)	0	0	0.02
Hyponatremia	3 (9.4)	0	4 (12.5)	3 (9.4)	2 (6.3)	0	17 (53.1)	1 (3.1)	2 (6.3)	0.07
Malnutrition	37 (29.6)	0	15 (12.0)	18 (14.4)	5 (4.0)	0	46 (36.8)	2 (1.6)	2 (1.6)	0.01
Acute renal failure	5 (7.7)	0	21 (32.3)	3 (4.6)	3 (4.6)	4 (6.2)	27 (41.5)	0	2 (3.1)	0.01
Hypernatremia	1 (25.0)	0	0	1 (25.0)	0	1 (25.0)	1 (25.0)	0	0	0.037
Hypoglycemia	1 (8.3)	0	10 (83.3)	0	0	0	1 (8.3)	0	0	0.14
Polycythemia	0	0	0	0	0	0	8 (100.0)	0	0	0.08
Gastroenteritis	5 (45.5)	0	3 (27.3)	0	0	0	3 (27.3)	0	0	0.835

¹Pearson χ²-tests.

MDS: Myelodysplastic syndrome; CAD: Coronary artery disease; CVO: Cerebrovascular disease; COPD: Chronic obstructive pulmonary disease.

DISCUSSION

Approximately 50% of individuals over the age of 75 meet the present diagnostic criteria for chronic kidney disease. Yet, considering them all as ill is debatable[14]. A lack of an exact definition of the standard GFR range for the elderly results in overdiagnosing renal failure in the elderly population[15-17]. Categorization of elderly patients with age-dependent estimated GFR decrease as chronic kidney disease is crucial, as it increases the likelihood of unwarranted intervention with extra implications for healthcare practices and policies for most of this age group[15-17]. The GFR value of the patients in our study was 58.87 ± 30 mL/kg/1.73 m² at the time of hospitalization (P < 0.001). We also found that patients with (32.8%) and without (43.5%) comorbidities were most commonly hospitalized in G2 stage. This indicates that comorbid factors did not affect the GFR values of the hospitalized patients. The kidneys of patients with comorbidities appear to develop adaptive mechanisms to maintain the GFR.

In mortality studies in the elderly, low GFR has been evaluated as an important parameter[6]. This study did not investigate mortality. GFR-related hospitalization diagnostics were not affected by the presence of comorbid factors. We interpreted this situation as the protective adaptive mechanisms that develop over time in the elderly with concomitant diseases and the positive effects of the drugs used on mortality. There was no significant difference in comorbidities between men and women (P = 0.078). Of the hospitalized patients, 147 (24.5%) had no comorbidities. Diabetes (n = 166, 27.7%) and arterial hypertension (n = 168, 28%) were more prevalent. Our study found a significant difference only between patients without comorbidities (67.4 ± 27.4 mL/kg/1.73 m²) and those with diabetes (53.5 ± 28.3 mL/kg/1.73 m², P = 0.001) and cancer (41.6 ± 18.6 mL/kg/1.73 m², P = 0.03). This difference can be attributed to the high frequency of diabetes in our study population and the low frequency of cancer patients. Hospitalization of cancer patients occurred at G3b stage (54.5%), while diabetes patients were hospitalized at G2 stage (25.9%).

Our study discovered that GFR values during hospitalization had no impact on the clinical diagnosis of hospitalization in the population over 75 years of age. Anemia and malnutrition were the most frequent hospitalization diagnoses across all GFR stages. Among women and men, anemia (34.4% and 28.6%, respectively) and malnutrition (20.9% and 20.8%, respectively) were the most common causes of hospitalization. The hospitalization diagnoses of male and female patients did not show a notable difference (P = 0.308). The similar hospitalization diagnoses in all patients were attributed to gastrointestinal system absorption and function disorders that developed due to their advanced age and were independent of comorbid factors. This is why diagnoses of anemia and malnutrition were common. Earlier studies focused primarily on the relationship between low GFR, mortality, and comorbid factors. Mortality was found to increase as GFR decreased[18-20].

CONCLUSION

In conclusion, the natural process of aging, coupled with a lack of effective healthcare policies, reduces the standard of living for senior citizens. If preventive medicine is not administered to healthy elderly individuals, they are more likely to require hospitalization. Renal dysfunction is one of the most critical problems associated with aging. Our study aims to highlight the physiologically low GFR in the elderly rather than focusing on the mortality rate. Therefore, we assessed GFR based on various stages. The hospitalization diagnoses were similar in individuals with all stages of GFR. The presence of comorbidities did not affect GFR during hospitalization, according to our findings. We anticipate that our findings will add to the existing literature since we did not come across a study that was akin to ours. Our study indicates that the GFR at the time of diagnosis correlates with the age of the patient and aging of the kidney. Special GFR calculations should be carried out for patients aged 75 years and older, using distinct formulas not currently available. These calculations should take into account the physiological aging process of the kidney. The GFR value of patients in the study was determined using a single method. While there are several alternative methods to measure GFR and compare the value during hospitalization with that from 6 months prior, unavailable pre-hospitalization examinations limited our scope. Future studies should consider measuring GFR using various methods across larger population samples in narrower age ranges.