Acute kidney injury associated to sulfamethoxazole urine crystal: The importance of clinical suspicion.

Management of acute kidney injury (AKI) associated with drug-induced crystal nephropathy can be difficult, and timely diagnosis is critical to resolve this condition. We present the case of a 55-year-old woman with history of systemic lupus erythematosus (SLE), who, after treatment with trimethoprim/sulfamethoxazole (TMP/SMX) for suspected Pneumocystis jirovecii pneumonia, developed severe AKI. Automated urinary sediment initially reported hematuria, leukocyturia and "uric acid crystals". She did not have allergic symptoms, clinical manifestations of active SLE nor hyperuricemia. AKI persisted despite volume expansion with crystalloids. Due to SMX exposure, it was suspected that "uric acid crystals" could be in reality "SMX crystals", and were a possible cause of crystal nephropathy. TMP/SMX was withheld and urinary alkalization was performed, with subsequent resolution of AKI. SMX urine crystals were posteriorly confirmed by Fourier transform infrared spectroscopy.

Estimación de la función renal para la dosificación de drogas / Estimation of kidney function to adjust drug dosing

Drug dosing according to renal function is a globally accepted practice whose main purpose is to avoid drug associated toxicity when renal clearance is decreased. Renal function is usually estimated based on creatinine clearance or an estimated glomerular filtration rate (GFR) obtained from one of the available equations based on serum biomarkers. In this review we will analyze the different available methods to adjust the dose of drugs based on GFR, with emphasis on their comparative performance for this objective. Based on this, we will provide some recommendations for drug dosing in chronic and acute renal dysfunction.

[Estimation of kidney function to adjust drug dosing]. / Estimación de la función renal para la dosificación de drogas.

Drug dosing according to renal function is a globally accepted practice whose main purpose is to avoid drug associated toxicity when renal clearance is decreased. Renal function is usually estimated based on creatinine clearance or an estimated glomerular filtration rate (GFR) obtained from one of the available equations based on serum biomarkers. In this review we will analyze the different available methods to adjust the dose of drugs based on GFR, with emphasis on their comparative performance for this objective. Based on this, we will provide some recommendations for drug dosing in chronic and acute renal dysfunction.

Desempeño comparativo de ecuaciones de estimación de excreción urinaria de creatinina

Background: 24-hour urine collection accuracy is generally evaluated based on the values of urine creatinine (UCr) excretion, usually using ranges adjusted by weight. UCr excretion depends on several factors. Equations to estimate UCr in 24-hour collection (UCr/24h) that consider these factors have been developed. However, these formulas have not been evaluated in a sample of Latinamerican origin. Aim: To evaluate the performance of the existing UCr/24 h estimation equations in a sample of Latinamerican origin. Material and Methods: 24-hour urine collections from 181 ambulatory patients were analyzed. Measured UCr/24h was compared with estimated UCr (eUCr) through the equations of Ix (CKD-EPI), Gerber-Mann, Goldwasser, Cockcroft-Gault, Rule, Walser, Kawasaki, Tanaka and Huidobro. Performance of the nine equations to estimate UCr/24h was evaluated with the Pearson correlation and Lin concordance coefficients, and Bland-Altman method. Bias, precision, and accuracy (percentage of collections within 30% of measured UCr or P30) were also calculated. Results: Measured UCr/24h in the 181 patients was 1236 + 378 mg. Correlation coefficient (Pearson) of the eUCr/24h with the equations of Walser, Ix and Huidobro and the measured UCr/24h was strongly positive. Rule and Kawasaki equations had the lowest positive correlation coefficients. Bias was similar using the formulas of Walser, Goldwasser, Kawasaki, Ix and Huidobro. Walser, Ix, Huidobro, Cockcroft-Gault and Goldwasser equations had good accuracy (P30 > 85%), while Gerber-Mann, Tanaka, Rule and Kawasaki formulas had a P30 < 65%. Conclusions: Walser, Ix and Huidobro equations had the best performance to estimate UCr/24h excretion in a population of latinamerican origin.

[A new equation to estimate daily natriuresis from parameters in plasma and spot urine sample in the Chilean population]. / Nueva ecuación para la estimación de la natriuresis diaria a partir de parámetros en plasma y orina aislada en población chilena.

BACKGROUND: Excessive sodium intake is associated with increased cardiovascular morbidity and mortality. Daily sodium intake is usually inferred from sodium excretion in a 24-hour urine collection, which is cumbersome and prone to errors. Different formulas have attempted to estimate 24-hour urinary sodium from a spot urine sample. Unfortunately, their concordances are insufficient and have not been tested in our population. AIM: To develop an equation to predict 24-hour urine sodium from parameters in plasma and spot urine samples. To validate the equation and compare it with other formulas in Chilean population. MATERIAL AND METHODS: Analysis of 24-hour urine collections, plasma sample and spot urine sample from 174 adult outpatients (81% females) with an estimated glomerular filtration rate (eGFR) ≥ 60 mL/min/1.73m2. These were collected between 2015 and 2019 using standardized methods and educating patients about the correct method to collect 24 h urine samples. In all these patients, creatinine and electrolytes were measured in plasma and urine. A new equation was developed using a multiple linear regression model. RESULTS: Twenty-four-hour urine sodium excretion was significantly correlated with age, weight, height, eGFR, plasma osmolarity, urine electrolytes and parameters obtained from spot urine sample, among others. The new equation had a linear correlation with 24-hour natriuresis of 0.91 and the concordance was 0.9. The predictive capacity of the new equation was better than the existing formulas. CONCLUSIONS: We developed a formula to accurately predict daily natriuresis in the Chilean population.

[Comparison of different methods to estimate glomerular filtration rate in older adults]. / ¿Son equivalentes los diferentes métodos para estimar la función renal en los adultos mayores?

BACKGROUND: Glomerular filtration rate (GFR) estimation in older adults using a creatinine clearance/24-hour (CrCl) or an equation based on serum creatinine, are often considered equivalent by clinicians. AIM: To compare GFR estimated (eGFR) with the available equations and measured CrCl in patients ≥ 70 years. A secondary aim was to know the differences in chronic kidney disease (CKD) classification, when using the different eGFR formulas. PATIENTS AND METHODS: In 144 patients aged 77 ± 5 years (58% men), CrCl was measured and GFR was estimated using MDRD, CKD-EPI, BIS-1 and FAS formulas. The eGFR and the stage of CKD were compared according to the different equations used. RESULTS: GFR estimated by MDRD and CKD-EPI equations was 7.8 and 8.4 mL/min/1.73 m2 lower than 24-hour ClCr, respectively. This difference was even greater using the BIS-1 and FAS equations. Twenty-four-hour CrCl classified 47.2% of the patients in a category of renal function > 60 mL/min/1.73 m2, while MDRD and CKD-EPI equations classified just over a third, and BIS-1 and FAS formulas around 20% of the patients. CONCLUSIONS: The practice of considering equivalent the GFR estimation using the creatinine-based equations with measured creatinine clearance in older adults should be reconsidered, because their results differ markedly.

[Performance of formulas for the evaluation of 24-hour urine collections using urine creatinine excretion]. / Evaluación de la recolección de orina de 24 horas a partir de la creatininuria: fórmulas para estimarla y su rendimiento.

Creatinine excretion is widely used as a method to evaluate the adequacy of urine collection in different clinical settings. Many factors influence its elimination, such as protein intake, exercise, muscle mass, age, and sex, among many others. As 24-hour urine collections can be cumbersome, several equations have been developed to aid clinicians to correctly interpret results derived from them. In this review article, we report the factors that can modify creatinine excretion and we evaluate the accuracy of different published equations to estimate 24-hour urine creatinine excretion.

[Evaluation of kidney function in older adults]. / Evaluación de la función renal en adultos mayores.

The evaluation of renal function in older adults is usually carried out with a creatinine clearance or an estimation of glomerular filtration rate using formulas such as Cockcroft-Gault, MDRD or CKD-EPI. The results obtained with these formulas are often regarded as equivalent. However, in adults older than 70 years, the Cockcroft-Gault formula frequently underestimates the glomerular filtration rate with respect to reference methods and the MDRD formula overestimates it. CKD-EPI has a more unpredictable behavior. This leads to erroneously classifying patients in the stages of chronic kidney disease (CKD), artificially increasing the prevalence of this condition, overloading health systems and generating emotional disorders in patients mistakenly classified as carriers of CKD. Also, when kidney function is overestimated, CKD patients are prevented from receiving the treatments appropriate for their condition. In recent years, new formulas have been proposed (FAS, BIS) with a greater accuracy to estimate glomerular filtration rate in older adults. This review describes the behavior of these formulas in a significant number of older adults, from various countries, and proposes using those equations with the best performance in older adults.

[Use of cystatin C to estimate glomerular filtration rate]. / Uso de la cistatina C como biomarcador para estimar la tasa de filtración glomerular.

Glomerular filtration rate (GFR) is routinely estimated using endogenous biomarkers due to the complexity of direct measurement methods. Cystatin C is a protease inhibitor produced in all nucleated cells. It is freely filtered and then catabolized by renal tubular cells. Therefore, plasma concentration of cystatin C depends primarily on GFR. Serum cystatin C is less affected by muscle mass, diet, race, gender and age than creatinine. In the general population, equations to estimate GFR based on cystatin C do not have a better performance than those based on creatinine. However, formulas that combine creatinine and cystatin C are more accurate and precise. Estimation of GFR based on cystatin C could be useful in populations in which creatinine value may be biased, such as people with extremely low or high muscle mass, cirrhosis and chronic cardiorenal syndrome. Due to its higher cost in comparison to creatinine, we recommend measuring cystatin C on these clinical situations and when a more accurate estimation of GFR is required.

Diagnosis of light chain cast nephropathy through immunostaining of the urine: Perfecting the "liquid biopsy".

Light chain (LC) cast nephropathy is the main cause of kidney injury and an important determinant of poor survival in patients with multiple myeloma (MM). It is usually suspected when an MM patient with elevated serum concentration of free LC presents kidney failure, but it often requires confirmation by kidney biopsy. We report the case of a 73-year-old woman who presented with fatigue, weight loss, and constipation. Laboratory exams revealed anemia, hypercalcemia, and kidney failure. Urine sediment analysis demonstrated irregular crystalline "waxy type" casts. With the hypothesis of LC cast nephropathy, immunostaining of the urine sediment was performed. The analysis revealed several rectangular and irregular casts with intense and bright stain for λ LCs only. A myelogram was performed, showing extensive occupation of the bone marrow by plasma cells; and immunofixation in urine and serum revealed monoclonal IgG-λ component, confirming the diagnosis of IgG-λ MM. This case highlights the potential utility of the urine sediment analysis and immuno-staining as a reliable non-invasive alternative method for diagnosis of cast nephropathy in patients with monoclonal gammopathies.

Evaluación de la función renal en adultos mayores / Evaluation of kidney function in older adults

The evaluation of renal function in older adults is usually carried out with a creatinine clearance or an estimation of glomerular filtration rate using formulas such as Cockcroft-Gault, MDRD or CKD-EPI. The results obtained with these formulas are often regarded as equivalent. However, in adults older than 70 years, the Cockcroft-Gault formula frequently underestimates the glomerular filtration rate with respect to reference methods and the MDRD formula overestimates it. CKD-EPI has a more unpredictable behavior. This leads to erroneously classifying patients in the stages of chronic kidney disease (CKD), artificially increasing the prevalence of this condition, overloading health systems and generating emotional disorders in patients mistakenly classified as carriers of CKD. Also, when kidney function is overestimated, CKD patients are prevented from receiving the treatments appropriate for their condition. In recent years, new formulas have been proposed (FAS, BIS) with a greater accuracy to estimate glomerular filtration rate in older adults. This review describes the behavior of these formulas in a significant number of older adults, from various countries, and proposes using those equations with the best performance in older adults.

Nueva ecuación para la estimación de la natriuresis diaria a partir de parámetros en plasma y orina aislada en población chilena / A new equation to estimate daily natriuresis from parameters in plasma and spot urine sample in the Chilean population

Background: Excessive sodium intake is associated with increased cardiovascular morbidity and mortality. Daily sodium intake is usually inferred from sodium excretion in a 24-hour urine collection, which is cumbersome and prone to errors. Different formulas have attempted to estimate 24-hour urinary sodium from a spot urine sample. Unfortunately, their concordances are insufficient and have not been tested in our population. Aim: To develop an equation to predict 24-hour urine sodium from parameters in plasma and spot urine samples. To validate the equation and compare it with other formulas in Chilean population. Material and Methods: Analysis of 24-hour urine collections, plasma sample and spot urine sample from 174 adult outpatients (81% females) with an estimated glomerular filtration rate (eGFR) ≥ 60 mL/min/1.73m2. These were collected between 2015 and 2019 using standardized methods and educating patients about the correct method to collect 24 h urine samples. In all these patients, creatinine and electrolytes were measured in plasma and urine. A new equation was developed using a multiple linear regression model. Results: Twenty-four-hour urine sodium excretion was significantly correlated with age, weight, height, eGFR, plasma osmolarity, urine electrolytes and parameters obtained from spot urine sample, among others. The new equation had a linear correlation with 24-hour natriuresis of 0.91 and the concordance was 0.9. The predictive capacity of the new equation was better than the existing formulas. Conclusions: We developed a formula to accurately predict daily natriuresis in the Chilean population.

Evaluación de la recolección de orina de 24 horas a partir de la creatininuria: fórmulas para estimarla y su rendimiento / Performance of formulas for the evaluation of 24-hour urine collections using urine creatinine excretion

Creatinine excretion is widely used as a method to evaluate the adequacy of urine collection in different clinical settings. Many factors influence its elimination, such as protein intake, exercise, muscle mass, age, and sex, among many others. As 24-hour urine collections can be cumbersome, several equations have been developed to aid clinicians to correctly interpret results derived from them. In this review article, we report the factors that can modify creatinine excretion and we evaluate the accuracy of different published equations to estimate 24-hour urine creatinine excretion.

¿Son equivalentes los diferentes métodos para estimar la función renal en los adultos mayores? / Comparison of different methods to estimate glomerular filtration rate in older adults

Background: Glomerular filtration rate (GFR) estimation in older adults using a creatinine clearance/24-hour (CrCl) or an equation based on serum creatinine, are often considered equivalent by clinicians. Aim: To compare GFR estimated (eGFR) with the available equations and measured CrCl in patients ≥ 70 years. A secondary aim was to know the differences in chronic kidney disease (CKD) classification, when using the different eGFR formulas. Patients and Methods: In 144 patients aged 77 ± 5 years (58% men), CrCl was measured and GFR was estimated using MDRD, CKD-EPI, BIS-1 and FAS formulas. The eGFR and the stage of CKD were compared according to the different equations used. Results: GFR estimated by MDRD and CKD-EPI equations was 7.8 and 8.4 mL/min/1.73 m2 lower than 24-hour ClCr, respectively. This difference was even greater using the BIS-1 and FAS equations. Twenty-four-hour CrCl classified 47.2% of the patients in a category of renal function > 60 mL/min/1.73 m2, while MDRD and CKD-EPI equations classified just over a third, and BIS-1 and FAS formulas around 20% of the patients. Conclusions: The practice of considering equivalent the GFR estimation using the creatinine-based equations with measured creatinine clearance in older adults should be reconsidered, because their results differ markedly.

Uso de la cistatina C como biomarcador para estimar la tasa de filtración glomerular / Use of cystatin C to estimate glomerular filtration rate

Glomerular filtration rate (GFR) is routinely estimated using endogenous biomarkers due to the complexity of direct measurement methods. Cystatin C is a protease inhibitor produced in all nucleated cells. It is freely filtered and then catabolized by renal tubular cells. Therefore, plasma concentration of cystatin C depends primarily on GFR. Serum cystatin C is less affected by muscle mass, diet, race, gender and age than creatinine. In the general population, equations to estimate GFR based on cystatin C do not have a better performance than those based on creatinine. However, formulas that combine creatinine and cystatin C are more accurate and precise. Estimation of GFR based on cystatin C could be useful in populations in which creatinine value may be biased, such as people with extremely low or high muscle mass, cirrhosis and chronic cardiorenal syndrome. Due to its higher cost in comparison to creatinine, we recommend measuring cystatin C on these clinical situations and when a more accurate estimation of GFR is required.

[Comparative performance of urinary creatinine excretion estimating equations]. / Desempeño comparativo de ecuaciones de estimación de excreción urinaria de creatinina.

BACKGROUND: 24-hour urine collection accuracy is generally evaluated based on the values of urine creatinine (UCr) excretion, usually using ranges adjusted by weight. UCr excretion depends on several factors. Equations to estimate UCr in 24-hour collection (UCr/24h) that consider these factors have been developed. However, these formulas have not been evaluated in a sample of Latinamerican origin. AIM: To evaluate the performance of the existing UCr/24 h estimation equations in a sample of Latinamerican origin. MATERIAL AND METHODS: 24-hour urine collections from 181 ambulatory patients were analyzed. Measured UCr/24h was compared with estimated UCr (eUCr) through the equations of Ix (CKD-EPI), Gerber-Mann, Goldwasser, Cockcroft-Gault, Rule, Walser, Kawasaki, Tanaka and Huidobro. Performance of the nine equations to estimate UCr/24h was evaluated with the Pearson correlation and Lin concordance coefficients, and Bland-Altman method. Bias, precision, and accuracy (percentage of collections within 30% of measured UCr or P30) were also calculated. RESULTS: Measured UCr/24h in the 181 patients was 1236 + 378 mg. Correlation coefficient (Pearson) of the eUCr/24h with the equations of Walser, Ix and Huidobro and the measured UCr/24h was strongly positive. Rule and Kawasaki equations had the lowest positive correlation coefficients. Bias was similar using the formulas of Walser, Goldwasser, Kawasaki, Ix and Huidobro. Walser, Ix, Huidobro, Cockcroft-Gault and Goldwasser equations had good accuracy (P30 > 85%), while Gerber-Mann, Tanaka, Rule and Kawasaki formulas had a P30 < 65%. CONCLUSIONS: Walser, Ix and Huidobro equations had the best performance to estimate UCr/24h excretion in a population of latinamerican origin.

Impacto de la modalidad de terapia de reemplazo renal en adultos mayores frágiles / Impact of renal replacement therapy on frail older adults

INTRODUCCIÓN: La enfermedad renal crónica terminal está aumentando en los adultos mayores. La fragilidad es altamente prevalente en los adultos mayores con enfermedad renal crónica terminal. Sin embargo, no existen estudios prospectivos que comparen el rendimiento de las diferentes modalidades de terapia de reemplazo renal (TRR) en adultos mayores frágiles. OBJETIVO: Comparar la ocurrencia de resultados clínicamente relevantes (hospitalizaciones, caídas, fracturas de caderas y mortalidad) en adultos mayores prefrágiles y frágiles según modalidad de TRR: hemodiálisis o diálisis peritoneal. MÉTODO: Estudio observacional prospectivo en adultos mayores prefrágiles y frágiles (según escala FRAIL) en hemodiálisis y diálisis peritoneal en las unidades correspondientes de la Red de Salud UC-Christus. Se evaluaron características basales (edad, Charlson, índice de masa corporal, tiempo en TRR, cumplimiento de Kt/V, hemoglobina y albúmina) y se siguieron a 12 meses, registrando mortalidad, días y número de hospitalizaciones, caídas y fracturas de cadera. RESULTADOS: Cumplieron criterios de ingreso 27 pacientes por grupo. Sus características basales fueron similares, a excepción de la albuminemia y del tiempo en TRR, ambas menores en el grupo en diálisis peritoneal. La escala FRAIL fue similar. La escala FRAIL se correlacionó basalmente con mayor comorbilidad, menor albuminemia y no cumplimiento del Kt/V, mientras que fue independiente de la edad, índice de masa corporal y tiempo en TRR. Los días y número de hospitalizaciones a 12 meses fueron similares para ambas modalidades de TRR. La supervivencia de ambos grupos fue similar. No hubo diferencias en caídas y ningún paciente tuvo fracturas de cadera. CONCLUSIONES: En adultos mayores prefrágiles y frágiles la modalidad de TRR no influyó en la ocurrencia de hospitalización, mortalidad, caídas ni fracturas de cadera

INTRODUCTION: End-stage renal disease prevalence is increasing in older adults. Frailty is highly prevalent in older adults with end-stage renal disease. However, there are no prospective studies comparing the performance of the different modalities of renal replacement therapy (RRT) in frail older adults. OBJECTIVE: To compare clinically relevant outcomes (hospital admission, falls, hip fractures, and mortality) in prefrail and frail older adults according to the modality of RRT: peritoneal dialysis or haemodialysis. METHODS: A prospective observational study in prefrail and frail older adults (according to FRAIL scale) on peritoneal dialysis and haemodialysis was carried out. An evaluation was made using baseline characteristics (age, Charlson, body mass index, time on RRT, compliance with Kt/V dose, haemoglobin, and albumin). The patients were followed-up over 12 months, recording mortality, days and number of hospital admissions, falls, and hip fractures. RESULTS: A total of 54/65 (83%) older adults on RRT met criteria for prefrailty or frailty, and signed informed consent (27 in each modality). Baseline characteristics were similar, except for serum albumin and time on RRT, both of which were significantly lower in the peritoneal dialysis group. The FRAIL score was similar in both groups. Baseline FRAIL correlated with higher comorbidity, lower albumin levels, and non-compliance of Kt/V dose, while it was independent of age, body mass index, and time on RRT. Days and number of hospital admissions at 12 months were similar in patients on peritoneal dialysis and haemodialysis. Survival on peritoneal dialysis and haemodialysis was similar. There were no differences in falls or hip fractures. CONCLUSIONS: Pre-frail and frail older adults on peritoneal dialysis and haemodialysis have similar clinical outcomes

[Impact of renal replacement therapy on frail older adults]. / Impacto de la modalidad de terapia de reemplazo renal en adultos mayores frágiles.

INTRODUCTION: End-stage renal disease prevalence is increasing in older adults. Frailty is highly prevalent in older adults with end-stage renal disease. However, there are no prospective studies comparing the performance of the different modalities of renal replacement therapy (RRT) in frail older adults. OBJECTIVE: To compare clinically relevant outcomes (hospital admission, falls, hip fractures, and mortality) in prefrail and frail older adults according to the modality of RRT: peritoneal dialysis or haemodialysis. METHODS: A prospective observational study in prefrail and frail older adults (according to FRAIL scale) on peritoneal dialysis and haemodialysis was carried out. An evaluation was made using baseline characteristics (age, Charlson, body mass index, time on RRT, compliance with Kt/V dose, haemoglobin, and albumin). The patients were followed-up over 12 months, recording mortality, days and number of hospital admissions, falls, and hip fractures. RESULTS: A total of 54/65 (83%) older adults on RRT met criteria for prefrailty or frailty, and signed informed consent (27 in each modality). Baseline characteristics were similar, except for serum albumin and time on RRT, both of which were significantly lower in the peritoneal dialysis group. The FRAIL score was similar in both groups. Baseline FRAIL correlated with higher comorbidity, lower albumin levels, and non-compliance of Kt/V dose, while it was independent of age, body mass index, and time on RRT. Days and number of hospital admissions at 12 months were similar in patients on peritoneal dialysis and haemodialysis. Survival on peritoneal dialysis and haemodialysis was similar. There were no differences in falls or hip fractures. CONCLUSIONS: Pre-frail and frail older adults on peritoneal dialysis and haemodialysis have similar clinical outcomes.

[Effects of creatine supplementation on renal function]. / Efectos en la función renal de la suplementación de creatina con fines deportivos.

Creatine supplements may transitorily rise serum creatinine levels and mimic a kidney disease. If its use is associated with a high protein diet, the resulting increase in blood urea nitrogen will increase the confusion. Since clinical laboratories usually inform the estimated glomerular filtration rate based on serum creatinine, its elevation may lead to over diagnose a chronic renal failure, with the inherent personal and public health consequences. Creatine supplements are safe and do not cause renal disease. Reports of kidney damage associated with its use are scanty. However, creatine supplements should not be used in people with chronic renal disease or using potentially nephrotoxic medications.

Reserva funcional renal: concepto y aplicabilidad potencial en la práctica clínica / Renal functional reserve: concept and potential application in clinical practice

Renal functional reserve (RFR) is the capacity of the kidney to increase its glomerular filtration rate (GFR) in response to physiological or pathological stimuli. The most commonly used stimuli to assess this reserve are an oral load of proteins of animal origin, amino acid infusions, dopamine, glucagon or combinations of them. RFR is calculated as the difference between stimulated and baseline GFR. Vegetarians have lower baseline GFR than the general population and an increased RFR. Subjects with only one kidney and those suffering from chronic nephropathies usually have a reduced or absent RFR despite having normal basal GFR. Quantification of RFR may be useful to detect subclinical renal damage, physiological conditions that reduce baseline GFR, evaluation of potential donors for kidney transplantation, suspected hyperfiltration, detection of renal lability against acute injuries or pregnancy and the evaluation after an acute renal injury when renal function seems to be recovered and residual subclinical damage is suspected.