database, or admission creatinine value 100 0 Cruz55 2164 multi cr+uo retrieved from hospital database, or estimated by MDRD formula 78 22 Perez-Valdivieso56 1008 single cr estimated by MDRD formula 0 100 Kuitunen57 813 single cr+uo preoperative value 100 0 Coca58 304 single cr the lowest s-creatinine value in the first 5 hospital days 100 0 Arnaoutakis59 267 single N/A N/A N/A N/A Abosaif60 247 single cr+uo retrieved from hospital database, or admission creatinine value 100 0 Maccariello61 214 multi cr+uo retrieved from hospital database, or estimated by MDRD formula N/A N/A Jenq62 134 single cr+uo admission creatinine value, or estimated by MDRD formula 90 10 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 Age (years) Black males mg/dl (lmol/l) Other males mg/dl (lmol/l) Black females mg/dl (lmol/l) Other females mg/dl (lmol/l) 20–24 1.5 (133) 1.3 (115) 1.2 (106) 1.0 (88) 25–29 1.5 (133) 1.2 (106) 1.1 (97) 1.0 (88) 30–39 1.4 (124) 1.2 (106) 1.1 (97) 0.9 (80) 40–54 1.3 (115) 1.1 (97) 1.0 (88) 0.9 (80) 55–65 1.3 (115) 1.1 (97) 1.0 (88) 0.8 (71) 465 1.2 (106) 1.0 (88) 0.9 (80) 0.8 (71) Estimated glomerular filtration rate=75 (ml/min per 1.73 m2 )=186 (serum creatinine [SCr]) 1.154 (age) 0.203 (0.742 if female) (1.210 if black)=exp(5.228 1.154 In [SCr]) 0.203 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 Kidney International Supplements (2012) 2, 19–36 29 chapter 2.4 presence of CKD. Furthermore, CKD and AKI may coexist. By using all available clinical data (laboratory, imaging, history, and physical exam) it should be possible to arrive at both an accurate diagnosis as well as an accurate estimate of baseline SCr. Importantly, excluding some cases of hemodilution secondary to massive fluid resuscitation (discussed below), the lowest SCr obtained during a hospitalization is usually equal to or greater than the baseline. This SCr should be used to diagnose (and stage) AKI. For example, if no baseline SCr was available in Case A, diagnosis of AKI could be made using the MDRD estimated SCr (Table 9). If Case A were a 70-year-old white female with no evidence or history of CKD, the baseline SCr would be 0.8 mg/dl (71 mmol/l) and a diagnosis of AKI would be possible even on day 1 (criterion 1, X50% increase from baseline). However, if the patient was a 20-year-old black male, his baseline SCr would be estimated at 1.5 mg/dl (133 mmol/l). Since his admission SCr is lower, this is assumed to be the baseline SCr until day 7 when he returns to his true baseline, and this value can be taken as the baseline. These dynamic changes in interpretation are not seen in epidemiologic studies, which are conducted when all the data are present, but are common in clinical medicine. Note that the only way to diagnose AKI (by SCr criteria) in Case H is to use an estimated SCr. Examples of application of AKI stages Once a diagnosis of AKI has been made, the next step is to stage it (Recommendation 2.1.2). Like diagnosis, staging requires reference to a baseline SCr when SCr criteria are used. This baseline becomes the reference SCr for staging purposes. Table 10 shows the maximum stage for each Case described in Table 7. Staging for Case A was already mentioned. The maximum stage is 2 because reference SCr is 1.0 mg/dl (88 mmol/l) and the maximum SCr is 2.0 mg/dl (177 mmol/l). Had the reference SCr been 0.6 mg/dl (53 mmol/ l), the maximum stage would have been 3. Case F was staged by using the lowest SCr (1.0 mg/dl [88 mmol/l]) as the reference. Of course, the actual baseline for this case might have been lower but this would not affect the stage, since it is already Stage 3. Note that if this patient was a 35-year-old white male, his MDRD estimated baseline SCr would be 1.2 mg/dl (106 mmol/l) (Table 9) and his initial stage on admission (day 1) would be assumed to be 2. However, once his SCr recovered to 1.0 mg/dl (88 mmol/l) on day 7, it would be possible to restage him as having had Stage 3. Once he has recovered, there may be no difference between Stage 2 or 3 in terms of his care plan. On the other hand, accurately staging the severity of AKI may be important for intensity of followup and future risk. Note that Cases G and H can only be staged if the reference SCr can be inferred. Case G may be as mild as stage 1 if the baseline is equal to the nadir SCr on day 7. On the other hand, if this case were a 70-year-old white female with no known evidence or history of CKD, the reference SCr would be 0.8 mg/dl (71 mmol/l)