Table 2.

Techniques for addressing missing baseline creatinine and their potential strengths and limitations (54,116)

Baseline CreatininePotential StrengthsPotential Limitations
Admission creatinine• Available in nearly all hospitalized patients (imputation not needed) • Less likely to be confounded by prolonged illness or hospitalization exposures compared with later values • Works well if admission kidney function “normal”• May underestimate incidence of AKI: can miss community-acquired AKI unless it worsens • Can underestimate AKI severity (stage) and erroneously assign a higher mortality per observed stage
Inpatient nadir creatinine• Available in nearly all hospitalized patients (imputation not needed) • More likely to detect community-acquired AKI that resolves • Normal values suggest preserved kidney function at baseline• May overestimate incidence and severity of AKI due to factors that confound serum creatinine (e.g., fluid overload or reduced generation of creatinine) • May erroneously assign a lower mortality per observed stage • May underestimate incidence and severity in patients with community-acquired AKI that does not resolve
Imputed creatinine using eGFR 75• Improves generalizability by allowing inclusion of patients who might otherwise be excluded• May overestimate AKI incidence, severity, and associated mortality depending on population, such as those with a higher prevalence of CKD • Can hinder accurate modeling by providing an estimate of kidney function distribution that is narrower than reality
Rolling 48-h or 7-d windows• Enriches for acuity • May be able to detect multiple episodes in a hospitalization• May miss or underestimate severity of community-acquired AKI or anchor to long-term kidney outcomes • May be difficult to stage accurately • May miss slowly evolving AKI
Preadmission baseline• Most likely to represent premorbid kidney function• Only available in select patients • CKD progression could be interpreted as AKI in some when sensitive definitions for AKI used or time horizon long • May be challenging to determine the true baseline in patients with multiple disparate values or who are frequently hospitalized