Identifying people with AKI at risk of malnutrition
There is currently no validated screening tool to identify malnutrition in people with AKI. However, the Renal Nutrition Screening Tool, RNST (Xia et al, 2016) and the Renal Inpatient Nutrition Screening Tool “Renal iNUT” (Jackson et al, 2019) are validated tools for use in people with kidney disease that are more sensitive than many other widely used generic tools. The Malnutrition Universal Screening Tool (MUST) is fairly specific and correlates well with other nutritional markers but lacks sensitivity when used with people with kidney impairment because weight and weight changes may be masked by fluid changes (Lawson et al, 2012).
In clinical practice, independently of the tool used, health care professionals caring for patients with AKI should use their clinical judgment to refer the patients to the dietitian if concerned about their nutritional status and/or intake.
Screening tools are often not appropriate in the critical care setting. Instead, the specialist critical care dietitian should routinely undertake nutritional assessment to determine patients’ nutritional risk and thereby those who will benefit the most from nutrition support (Segaran & Bear 2015).
In clinical practice AKI may be defined by severity (stage 1, 2 and 3) (NICE 2023) and cause of the injury – pre-renal, intra-renal and post-renal AKI (Rahman et al, 2012). The nutritional relevance of the cause of AKI is summarised in Table 1.
| Cause | Description | Nutritional relevance |
| Pre-renal AKI | Pre-renal injuries refer to anything which obstructs the flow of blood to the kidneys. Causes include reduced cardiac output; hypovolaemia; vascular emboli; heart failure; liver failure or drugs which affect the blood supply. Pre-renal injuries are often reversed within a couple of days once normal blood flow is restored. However, if the cause of the pre- renal injury is not reversed or treated effectively it may lead to an intrarenal injury. | There is typically no change in the nutritional requirements of patients with a pre-renal AKI. |
| Intra-renal AKI | Intra-renal injuries refer to anything which damages the cells of the kidney. Causes include nephrotoxic agents; infections or systemic diseases, e.g. lupus or sarcoidosis; acute tubular necrosis; glomerulonephritis. | This is a more severe form of injury and is likely to alter nutritional requirements. |
| Post-renal AKI | Post-renal injuries refer to anything, which obstructs the flow of urine from the kidneys. This often results in hydronephrosis (“water on the kidneys”). Causes include kidney stones; enlarged prostate; cervical cancer or tumours. Post-renal injuries are often reversed within a couple of days once the urinary obstruction is cleared. | There is typically no change in the nutritional requirements of patients with a post-renal AKI. |
Table 1. AKI terminology and nutritional relevance
Patients with pre-existing chronic kidney disease (CKD) may present with AKI. Acute illness in addition to underlying CKD is more likely to impact on and alter nutritional needs. These patients have an increased risk of worsening of their nutritional status when admitted with AKI and should be monitored closely (Meyer et al, 2020; Fiaccadori et al, 2021).