KDIGO Clinical Practice Guideline for Acute Kidney Injury
Examples of application of AKI definitions

Examples of application of AKI definitions

Table 7 illustrates a number of examples whereby patients presenting with possible AKI can be diagnosed. Cases A-F have a measurement of baseline SCr. To simplify decisionmaking, baseline estimated glomerular filtration rate (eGFR) exceeds 60 ml/min per 1.73 m² in these patients, so none has pre-existing CKD. Cases A-F can all be diagnosed with AKI by applying the first two criteria in Recommendation 2.1.1. (a documented increase of at least 0.3 mg/dl ( > 26.5 µmol/l) (within 48 hours or a 50% increase from presumed baseline). Note that a patient can be diagnosed with AKI by fulfilling either criterion 1 or 2 (or 3, urine output) and thus cases B,C,D, and F all fulfill the definition of AKI. Note also that patients may be diagnosed earlier using criterion 1 or 2. Early diagnosis may improve outcome so it is advantageous to diagnose patients as rapidly as possible. For example, case A can be diagnosed with AKI on day 2 by the first criterion, whereas the second criterion is not satisfied until day 3 (increase from 1.3 to 1.9). However, this is only true because the episode of AKI began prior to medical attention, and thus the day 1 SCr level was already increased. If creatinine measurements had available with 48 hours prior to day 1 and if this level had been at baseline (1.0 mg/dl [88.4 µmol/l]), it would have been possible to diagnose AKI on day 1 using the second criterion.

Cases F-H do not have a baseline measurement of SCr available. Elevated SCr (reduced eGFR) on day 1 of the hospitalization is consistent with either CKD or AKD without AKI. In Case F, baseline SCr can be inferred to be below the day 1 value because of the subsequent clinical course; thus, we can infer the patient has had an episode of AKI. In case G, AKI can be diagnosed by application of criterion 2, but the patient may have underlying CKD. Case H does not fulfill the definition for AKI based on either criteria, and has either CKD or AKD without AKI.

The example of Case A raises several important issues. First, frequent monitoring of SCr in patients at increased risk of AKI will significantly improve diagnostic time and accuracy. If Case A had not presented to medical attention (or if SCr had not been checked) until day 7, the case of AKI would likely have been missed. Frequent measurement of SCr in high-risk patients, or in patients in which AKI is suspected, is therefore encouraged—see Chapter 2.3. The second issue highlighted by Case A is the importance of baseline SCr measurements. Had no baseline been available it would still have been possible to diagnose AKI on day 3 (by either using criterion 2 or by using criterion 1 and accepting the baseline SCr as 1.3); however, not only would this have resulted in a

Table 7 | AKI diagnosis

Table 8 | Overview of the approaches to determine baseline SCr in the application of RIFLE classification in previous studies

cr, creatinine criteria; MDRD, Modification of Diet in Renal Disease; N/A, not available; pts, patients; SCr, serum creatinine; uo, urine output criteria.

Reprinted from Zavada J, Hoste E, Cartin-Ceba R et al. A comparison of three methods to estimate baseline creatinine for RIFLE classification. Nephrol Dial Transplant 2010; 25(12): 3911–3918 (Ref. 64) by permission from The European Renal Association-European Dialysis and Transplant Association; accessed http://ndt.oxfordjournals.org/content/25/12/3911.long

Table 9 | Estimated baseline SCr

Estimated glomerular filtration rate=75 (ml/min per 1.73 m²)=186 x (serum creatinine [S_Cr]) - 1.154 x (age) - 0.203 x (0.742 if female) x (1.210 if black)=exp(5.228 - 1.154 x In [S_Cr]) - 0.203 x In(age) - (0.299 if female) + (0.192 if black).

Reprinted from Bellomo R, Ronco C, Kellum JA et al. Acute renal failure - definition, outcome measures, animal models, fluid therapy and information technology needs: the Second International Consensus Conference of the Acute Dialysis Quality Initiative (ADQI) Group. Crit Care 2004; 8: R204-212 with permission from Bellomo R et al.²²; accessed http://ccforum.com/content/8/4/R204

delay in diagnosis, it would have resulted in a delay in staging (see Table 7). On day 7, it can be inferred that the patient’s baseline was no higher than 1.0 mg/dl (88 µmol/l) and thus correct staging of Case A as Stage 2 (two-fold increase from the reference SCr, see below and Table 7) on day 3 could have been determined in retrospect. However, if a baseline SCr was available to use as the reference, the correct stage could be determined on day 3.

Case B illustrates why criterion 2 can detect cases of AKI missed by criterion 1. It also clarifies why these cases are unusual. Had the SCr increased to 1.5 mg/dl (132.6 µmol/l) as opposed to peaking at 1.4 mg/dl (123.8 µmol/l), it would have been picked up by criterion 1 as well. By contrast Cases C, D, and even F illustrate how criterion 2 may miss cases identified by criterion 1. Note that Case F can only be diagnosed by inference. By day 7, it can be inferred that the baseline was no higher than 1.0 mg/dl (88 µmol/l) and thus it can be determined that the patient presented with AKI. However, if the baseline SCr could be estimated it would be possible to make this inference as early as day 1.