KDIGO Clinical Practice Guideline for Acute Kidney Injury
Pseudo-AKI

Pseudo-AKI. As with other clinical diagnoses defined by laboratory results (e.g., hyponatremia), the clinician must be cautious to interpret laboratory data in the clinical context. The most obvious example is with laboratory errors or errors in reporting. Erroneous laboratory values should obviously not be used to diagnose disease and suspicious lab results should always be repeated. Another example is when two SCr measurements are obtained by different laboratories. While the coefficient of variation for SCr is very small (< 5%) by various clinical testing methods, variation (bias) from one laboratory to the next may be considerably higher, although it is unlikely to approach 50%. Given that the SCr definition of AKI always uses at least two values, the variation and bias between each measure is further magnified—the coefficient of variation for comparison of two lab tests is equal to the square root of the sum of each coefficient squared. Although the international standardization of SCr measurements will largely eliminate interlaboratory bias in the future, care is needed in interpreting lab values obtained from different labs. Furthermore, daily variation in SCr due to differences in diet and activity may be as great as 10%. Finally, endogenous chromogens (e.g., bilirubin, ascorbic acid, uric acid) and exogenous chromogens and drugs (e.g., cephalosporins, trimethoprim, cimetidine) may interfere with the creatinine assay. The cumulative effect of these various factors influencing precision, bias, and biological variation may approach the level at which it could impact the diagnosis of AKI. A similar problem exists with urine output. Particularly outside the ICU, urine output is not often reported and urine collections may be inaccurate, especially in noncatheterized patients. Finally, as discussed in Chapter 2.1, a weight-based criterion for urine output will mean that some very obese patients will fulfill the definition of AKI without any kidney abnormality. Clinical judgment should always be exercised in interpreting such data.