Iohexol clearance for determination of glomerular filtration rate in rats induced to acute renal failure.

INTRODUCTION: The glomerular filtration rate (GFR) is considered an especially important tool for the measurement of renal function. Inulin clearance (InCl) is the classic reference method for this purpose, although it is associated with a number of disadvantages; thus, other markers have been proposed, including iohexol. Determination of iohexol clearance (IoCl) has been established for clinical use; however, its application as a GFR marker in experimental rat models has not been reported. OBJECTIVES: This study aims to standardize a methodology for the measurement of iohexol clearance and to evaluate its applicability as a marker of GFR in rats with induced toxic acute renal failure (ARF), using InCl as the gold standard. MATERIALS AND METHODS: Twenty-six Wistar male rats (200-300 g) were divided into the following two groups: a control group (n=7) and an ARF group (n=19). ARF was induced by the subcutaneous administration of cisplatin (5 mg/kg); IoCl and InCl were determined simultaneously, and plasma creatinine (pCreat) dosage was measured colorimetrically. RESULTS: The pCreat, InCl and IoCl levels were consistent with the expected values for the renal function ranges of the evaluated animals, and the IoCl and InCl levels were significantly correlated (r=0.792). An inverse moderate linear correlation between the IoCl and pCreat measurements (r=-0.587) and between the InCl and pCreat measurements (r=-0.722) were observed. CONCLUSION: These results confirm a correlation between IoCl and the gold standard of GFR, InCl measurement. IoCl offers a relevant advantage over InCl because determination of the former allows the animal to live after the procedure.

Adaptation of contrast injection protocol to tube potential for cardiovascular CT.

OBJECTIVE: The purpose of this study was to investigate and validate adaptation of a cardiovascular CT angiography contrast injection protocol for lower tube potential. MATERIALS AND METHODS: Eighty-three patients evaluated for thoracic aortic disease with a 256-MDCT scanner were imaged at 120 kV (group 1) or 100 kV (group 2) with the same contrast protocol (90 mL iopromide 370 mg I/mL at 3.5 mL/s). A pharmacokinetic model was validated and used to simulate aortic attenuation in group 2 patients with 20%, 33%, and 44% reduction in contrast volume. A 44% volume reduction was applied to 50 additional patients who underwent imaging at 100 kV (group 3). Patient characteristics, scanning and radiation parameters, and objective and subjective image indexes were compared among groups. RESULTS: Group 2 patients had higher mean aortic blood attenuation (399±61 HU) than group 1 patients (281±48 HU) (p<0.001) but similar image noise. Group 3 and group 1 patients had similar mean aortic attenuation and noise. Subjective assessment of image quality indicated that group 3 and group 1 had comparable percentages of images with good or excellent diagnostic confidence scores (reader 1, 98% vs 96%; reader 2, 96% vs 96%). CONCLUSION: Lower tube potential (100 kV) for cardiothoracic CT could be accompanied by a 44% reduction in contrast volume with satisfactory aortic blood-pool attenuation in most patients. More personalized adaptation of the contrast protocol that takes into account patient characteristics and tube potential is necessary to ensure sufficient contrast enhancement for all patients.

Avaliação do ritmo de filtração glomerular / Assessment of glomerular filtration rate

A medida do ritmo de filtração glomerular (RFG) é a prova laboratorial mais utilizada na avaliação da função renal. Para tanto, usam-se marcadores indiretos, como as determinações de creatinina e cistatina C no sangue, ou procede-se à determinação do RFG propriamente dito, com indicadores como inulina; contrastes iodados, marcados ou não; e outras substâncias. O exame mais solicitado para avaliação do RFG no laboratório de patologia clínica é a dosagem da creatinina sérica. Em algumas condições, entretanto, o resultado encontrado da creatinina sérica deve ser corrigido (através da utilização de fórmulas que levam em consideração características próprias do indivíduo) para ser devidamente interpretado. De fato, a inulina ainda é vista como marcador ideal de filtração glomerular, mas seu uso não se destina à prática clínica, de modo que ainda hoje persiste a busca por testes adequados para uso rotineiro.

Glomerular filtration rate (GFR) determination is the most frequently used laboratorial test to evaluate renal function. Indirect markers as blood determination of creatinine and cystatin C are used with this purpose, as well as the direct determination of GFR, with indicators like inulin; iodated contrasts, radioactive or not; and others. Serum creatinine is the test that is most commonly performed in order to evaluate GFR in the clinical pathology laboratory. However, in some conditions, aiming at the adequate interpretation of the test, the result of serum creatinine must be corrected (by using formulas that include individual characteristics of the subjects). In fact, inulin is still seen as the ideal marker of glomerular filtration, but its use is not directed to clinical practice; then the search for appropriate tests for routine use continues.