An analysis of the Urea to Creatinine Ratio (UCR) in different cardiac surgeries

Lavanya k

Clinical Dietitian, Department of Clinical Nutrition & Dietetics, Kauvery Hospital, Heart city

Abstract

Serum creatinine and urea (Blood Urea Nitrogen-BUN) are the most important biomarkers in the assessment of pre-operative renal function and in the prediction of adverse outcomes in cardiac surgery. Many bio-markers have been studied to date but there is no surrogate for measurement of serum creatinine and urea in clinical practice because it is feasible and inexpensive. High levels of serum creatinine and urea and have been important preoperative risk factors for per and post-operative renal injury. In the future, there may emerge new definitions and tools for the early diagnosis of acute kidney injury based on a panel of novel bio-markers. As per Mahdi Najafi., et al., we should plan oral and enteral feedings for post operatibe Acute Kidney Injury (AKI) patients with the objective to reduce the urea and creatinine ratio.

Introduction

Urea is the primary metabolite derived from dietary protein and tissue protein turnover. Creatinine is the product of muscle creatinine catabolism. Both are relatively small molecules (60 and 113 Daltons, respectively) that distribute throughout total body water. ^[2] The biological role of urea in chronic kidney disease (CKD) remains contentious. Urea has traditionally been thought to be a relatively inert molecule, however, recent experimental data has suggested that it induces biochemical alterations with a potential impact on clinical outcomes. Due to their small molecular sizes, both creatinine and urea are filtered by the glomerulus. Creatinine is not reabsorbed and is excreted from the body, however, approximately 40–50% of urea is reabsorbed in the tubules, where it is linked to reabsorption of sodium and water. Because this process is regulated by both neuro hormonal activity and renal function, the urea-to-creatinine ratio (UCR) has been proposed to be of value in clinical practice. In renal failure, serum urea and creatinine levels usually rise proportionally with a progressive decline in renal function. Serum urea levels can be further increased by excess protein intake, hypovolemia, heart failure, gastrointestinal bleeding and catabolism. Increases in serum urea out of proportion to serum creatinine result in an elevated UCR and reflect a critical condition ^[3]

The specific relationship between different postoperative urea and creatinine levels and prognosis for patients is not fully understood. Given that AKI is one of the most common major complications after cardiac surgery, it can cause increased morbidity and mortality, so we designed this study to investigate the correlation between different postoperative urea and creatinine (maximum, minimum, initial) and the outcome of cardiac surgery patients^[4]

Methodology

Bio-Markers for Post-Operative Cardiac Patients

Acute kidney injury (AKI) is a frequent complication of cardiac surgery and increases morbidity and mortality.

The identification of reliable biomarkers that allow earlier diagnosis of AKI in the postoperative period may increase the success of therapeutic interventions ^[^5]. New biomarkers exhibited a potential role in the early diagnosis of acute kidney injury recovery. Urine HGF, IGFBP-7, TIMP-2 and NGAL may improve our ability to predict the odds and timing of recovery and eventually renal support withdrawal. Acute kidney injury recovery requires more study, and its definition needs to be standardized to allow for better and more powerful research on biomarkers because some of them show potential for the prediction of acute kidney injury recovery ^[6]

As markers of renal function creatinine, urea, uric acid and electrolytes are for routine analysis whereas several studies have confirmed and consolidated the usefulness of markers such as cystatin C, β-Trace Protein ^[7]

Physiology of urea and Blood Urea Nitrogen test

Urea nitrogen is a waste product that your kidneys remove from your blood. Higher than normal BUN levels may be a sign that your kidneys aren’t working well. People with early kidney disease may not have any symptoms. A BUN test can help uncover kidney problems at an early stage when treatment can be more effective.

Blood urea nitrogen (BUN) is a medical test that measures the amount of urea nitrogen found in blood.

Physiology of creatinine

Creatinine is a non-protein nitrogenous compound that is produced by the breakdown of creatine in muscle. Creatinine is found in serum, plasma, and urine and is excreted by glomerular filtration at a constant rate and in the same concentration as in plasma.

Creatine is a chemical made by the body and is used to supply energy mainly to muscles. This test is done to see how well your kidneys work. Creatinine is removed from the body entirely by the kidneys. If kidney function is not normal, the creatinine level in your blood will increase.

Ureaand creatinine are both freely filtered at the glomerulus
Creatinine is not reabsorbed
Urea reabsorbed by tubules via regulation
Can be used as an indicator of the likely cause of renal failure

Glomerular Filtration Rate

Serum creatinine is also utilized in GFR estimating equations such as the Modified Diet in Renal Disease (MDRD) and the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation. These eGFR equations are superior to serum creatinine alone since they include race, age, and gender variables. GFR is classified into the following stages based on kidney disease.

Kidney Disease Improving Global Outcomes (KDIGO) stages of chronic kidney disease (CKD):

Stage 1 GFR greater than 90 ml/min/1.73 m²
Stage 2 GFR-between 60 to 89 ml/min/1.73 m²
Stage 3a GFR 45 to 59 ml/min/1.73 m²
Stage 3b GFR 30 to 44 ml/min/1.73 m²
Stage 4 GFR of 15 to 29 ml/min/1.73 m²
Stage 5 GFR less than 15 ml/min/1.73 m² (end-stage renal disease)

This provides an easier estimation of GFR without the collection of urine or the use of exogenous materials. However, as they utilize serum creatinine, they are also affected by the issues around serum creatinine measurement; hence the correction for the race, gender, and age is required.

Materials and Methods

Within the current investigation, the urea levels of the eight cardiac surgery patients (n = 8) in both the non-survivor and survivor groups were significantly greater than the 10–50 mg/dl cutoff.

Statistics of Blood Urea Level (Referral range 10–50mg/dl.)

S No	Types of surgeries	Last date of investigations	Investigation report
1	Bentall	20-Jan-24	453
2	Post CABG	25-Jan-24	378
3	Post CABG	09-Feb-24	172
4	Post CABG	21-Feb--24	147.66
5	Post CABG	02-Feb-24	66.34
6	Post CABG	15-Apr-24	50.8
7	Post MVR	19-Feb-24	96.4
8	Post AVR	14-Apr-24	53.5

The cardiac surgery patients (n = 10) in the current study had urea levels that were significantly greater than the 0.3 – 1.4 mg/dl cutoff in both the survivor and non-survivor groups.

S No	Types of surgeries	Last date of investigations	Investigation report
1	Bentall	20-Jan-24	7.83
2	Post CABG	25-Jan-24	7.19
3	Post CABG	01-Feb-24	1.57
4	Post CABG	05-Feb-24	1.64
5	Post MVR	19-Feb-24	2.16
6	Post DVR	21-Feb-24	3.93
7	Post CABG	26-Feb-24	1.73
8	Post CABG	17-Apr-24	1.61
9	Post DVR	20-Apr-24	1.91
10	Post CABG	21-Apr-24	1.93

Statistics of Serum Creatinine (Referral range 0.5–1.4 Mg/dl.)

The above graphic shows that the urea and creatinine ratios were greater following procedures other than valve replacement therapy when compared to all cardiac surgeries.

Result and discussion

Moreover, urea and creatinine are the mainstays in predicting risk models, and risk factor reduction has enhanced its importance in outcome prediction. According to this urea and creatinine ratio, we should plan the oral and enteral feedings for post-operative renal injury patients to reduce the urea and creatinine ratio.

Menu planning for post-operative renal injured patients (Oral)

Day	Types of therapeutic diet	Energy	Protein	Fat	Fluid
1	Clear Liquid Diet	800 Kcal	-	-	675 ml
2	Normal Liquid Diet	1450 Kcal	0.7g / Kg	0.2g /Kg	750 ml
3	Semisolid Diet	1750 Kcal	1g /Kg	0.4g/Kg	750 - 1000ml
4	Soft Diet	2000 Kcal	1.2g /Kg	0.6g/Kg	1000 ml

Principles of Diet

Adequate calorie, Moderate protein, Low fat, Moderate carbohydrate, Moderate fiber, Restricted sodium & potassium and Restricted fluid diet.

Foods to be avoided

Green Leafy Vegetables.
Cruciferous Vegetables.
High fluid content fruits like Citrus fruits.
Limited Red meat.
Limited Pulses.
Limit water consumption.

Enteral feeding for post-operative renal injured patients

Everyone agrees that a patient’s clinical outcome is influenced by their dietary support, which is a necessity for patients in intensive care. Malnutrition increases the risk of infectious morbidity and mortality in critically sick patients by impairing their immune system and ventilator drive, which prolongs the need for a ventilator. Enteral nutrition is an active therapy that positively affects the immune system and reduces the organism’s metabolic reaction to stress. In most circumstances, it is favored over parenteral nutrition due to its lower cost and better patient outcomes, including shorter hospital stays, lower rates of severe complications, and shorter lengths of stay. Reviewing the utilization of enteral feeding in critically sick patients was the goal of this paper.

In enteral feeding, we provide only Supplements or formula feed to the patients. Recommended allowance was met out by using formula feed.

S.no	Feed	Energy	Protein	Fat	Fluid
1	Protein Supplement	1600 Kcal	1g/Kg	1g/Kg	900 ml

Conclusion

RFT-elevated patients are very susceptible to morbidity and mortality rates, according to recent studies. Therefore, we should keep an eye on their dietary habits both before and after surgery and routinely look into the kidney function test results. Our focus should be on their urine production and hydration intake. That means we should feed them a diet low in fat, low in sodium, moderate in protein, and adequate in calories.

References

[1]. M Najafi – World journal of cardiology, 2014 – ncbi.nlm.nih.gov

[2]. . AO Hosten – Clinical Methods: The History, Physical, and Laboratory examinations, 1990 – ncbi.nlm.nih.gov

[3]. EM Brookes, DA Power – Scientific Reports, 2022 – nature.com

[4]. J Hou, L Shang, S Huang, Y Ao, J Yao – Frontiers in, 2022 – frontiersin.org

[5]. CR Parikh, E Abraham, M Ancukiewicz – Journal of the, 2005 – journals.lww.com

[6]. Sérgio Mina Gaião1,2 and José Artur Osório de Carvalho Paiva1,2

[7]. S Gowda, PB Desai, SJ Shetty, VS Kagwad… – Italian Journal of Public …, 2011 – ijphjournal.it

Mrs. Lavanya k
Dietitian

An analysis of the Urea to Creatinine Ratio (UCR) in different cardiac surgeries

An analysis of the Urea to Creatinine Ratio (UCR) in different cardiac surgeries

Lavanya k

Journals