Diagnostic algorithms for grading acute kidney injury and staging the chronic kidney disease patient

image of Diagnostic algorithms for grading acute kidney injury and staging the chronic kidney disease patient
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The terminology in current use to describe the different severities of chronic kidney disease and acute kidney disease is confusing and is applied in different ways by different authorities. In veterinary medicine, staging systems have been used for defining heart failure where a modification of a system used in human medicine is routinely supplied. This chapter covers selecting dogs and cats to be staged or graded, IRIS grading system for the patient with AKI and the IRIS CKD staging system.

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12.1 The spectrum of acute kidney injury (AKI) from early kidney injury/dysfunction to kidney failure. Acute kidney failure is the most recognizable presentation of AKI, but identification of earlier stages of injury is critical for timely diagnosis and to facilitate more effective management.
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12.3 Serial changes in serum creatinine concentration and International Renal Interest Society (IRIS) acute kidney injury (AKI) grading in a dog with gentamicin-induced AKI as part of an experimental study. The IRIS AKI grading effectively categorized the sequential course of the AKI from inapparent to failure and subsequent recovery. The shaded area reflects the reference range for serum creatinine. (Data from )
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12.5 Effect of plasma creatinine concentration at presentation on long-term survival of cats with chronic kidney disease. Kaplan–Meier survival curves from 50 cats entered into a prospective study ( ). The cats have been divided into two groups on the basis of their initial plasma creatinine concentration at entry to the study as either Stage 2 (creatinine <250 μmol/l; all cats in this study had plasma creatinine concentrations >177 μmol/l) or Stage 3 (creatinine >250 μmol/l; all cats in this study had plasma creatinine concentrations <440 μmol/l).
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12.6 Venous blood pH measurements in cats with naturally occurring chronic kidney disease (CKD). Blood pH measurements were made using a patient-side monitor (iSTAT machine; SDI Devices Ltd, USA). The reference range devised from 28 aged normal cats was 7.27–7.44. None of the cats in Stage 2, 3 of 20 (15%) in Stage 3 and 10 of 19 (52.4%) in Stage 4 had venous blood pH below 7.27 and therefore were considered to be acidaemic. IRIS = International Renal Interest Society. (Data from )
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12.7 The distribution of plasma parathyroid hormone (PTH) concentrations in cats at different stages of chronic kidney disease (CKD). representing a cross-sectional study of 80 cats presenting to first-opinion practices at initial diagnosis of CKD. Plasma PTH concentrations were measured using an intact immunoradiometric assay (Allegro Intact PTH Assay, Nichol’s Institute Diagnostics, UK). The classification system was based on clinical presentation rather than plasma creatinine concentration. Nevertheless, plasma creatinine concentrations in the three groups were for the majority of cases equivalent to IRIS Stages 2, 3 and 4. PTH concentrations outside of the laboratory reference range were found in 47% of cats in Stage 2, 87% of cats in Stage 3 and 100% of cats in Stage 4. IRIS = International Renal Interest Society. (Reproduced with permission from )
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12.10 An algorithm applying the International Renal Interest Society (IRIS) staging system to a feline patient suspected of having chronic kidney disease. In the setting of a low value for plasma creatinine (<125 μmol/l in dogs or <140 μmol/l in cats), firm evidence of kidney disease would usually be morphological, such as abnormal renal architecture on survey radiographs, abnormal renal ultrasound findings, or biopsy diagnosis of renal disease. The classification of pre-renal azotaemia (generally due to dehydration or renal ischaemia) or post-renal azotaemia (generally due to ureteral or urethral obstruction, or rupture of part of the urinary tract) will depend on careful evaluation of history, physical examination and other clinical findings. This determination may require additional tests, based on clinical judgement. For example, radiographic studies and/or abdominal paracentesis (with analysis of ascitic fluid creatinine concentration) may be required to establish a diagnosis of ruptured urinary bladder in an azotaemic cat with a history of blunt abdominal trauma. The classification of azotaemia as renal is based on the presence of azotaemia with no identifiable pre-renal or post-renal causes. As a general guide, dogs and cats with renal azotaemia usually have a urine specific gravity <1.030. These abnormalities may include any pre-renal factor that leads to dehydration or systemic arterial hypotension or post-renal factors such as ureteral or urethral obstruction, or urinary tract rupture. RI = renal insufficiency; SG = urine specific gravity. Proteinuria substaging (see Figure 12.8 ): NP = non-proteinuric; BP = borderline proteinuric; P = proteinuric. Blood pressure substaging on risk of extra-renal damage (see Figure 12.9 ): N = normotensive; BH = borderline hypertensive; H = hypertensive; S = severely hypertensive.

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