Investigators Quantify Serum Creatinine Baseline Definition Impact on Mortality

August 18, 2020
Kenny Walter

Categorizing baseline SCr as the median value over the preadmission period could be the least biased estimate of the baseline renal function.

The mortality rate of patients suffering from kidney injuries could depend on how the serum creatinine (SCr) baseline level is defined.

A team, led by Olga LaszczyŃska, Institute of Public Health, University of Porto, used a joint model to investigate how different definitions of baseline serum creatinine could affect the association between an acute increase in inpatients’ SCr and the 30-day mortality rate, as well as whether this effect depends on premorbid SCr trajectory.

In the retrospective study, the investigators examined adults admitted to a tertiary acute-care hospital in Porto, Portugal between 2013-2015. Each patient had at least 2 preadmission ambulatory and 2 inpatient SCr measurements.

The investigators defined the baseline serum creatinine as the lowest, most recent, or the median value over the preadmission period.

The team used a joint model that combined a linear mixed model for repeated inpatient serum creatinine relative to baseline value and a Cox proportional survival model.

Preadmission serum creatinine courses were identified using linear regression and subsequently clustered based on a patient-specific slope. The researchers described preadmission SCr trajectories as median serum creatinine courses within clusters.

Overall, the investigators found serum creatinine trajectories were stable (78.0%), decreasing (11.3%), and increasing (10.7%). An increase in inpatient serum creatinine by 50% relative to baseline SCr at the lowest raised the risk of 30-day mortality by 74%.

However, the estimate was not different from hazard ratios obtained for the most recent measurement (1.78) or the median SCr measurement (1.71).

The investigators ultimately found no differences in hazard ratios across preadmission trajectories.

Currently, measuring albuminuria is the preferred method for defining and staging chronic kidney disease (CKD). However, measuring total urine protein or dipstick protein can be an alternative to albuminuria.

Recently, a University of Tennessee-led research team developed equations for converting urine protein-creatinine ratio (PCR) and dipstick protein to urine albumin-creatinine ratio (ACR) and tested their diagnostic accuracy in chronic kidney disease screening and staging.

The investigators found the link between PCR and ACR was inconsistent for PCR values less than 50 mg/g. For higher PCR values, the PCR conversion equations showed moderate sensitivity (91%, 75%, and 87%), as well as for specificity (87%, 89%m and 98%) for screening (ACR >30 mg/g) and classification into stages A2 and A3, respectively.

The investigators also found for individual risk prediction, the estimated two-year four-variable kidney failure risk equation using predicted ACR from PCR had discrimination similar to that of using observed ACR.

In the current study, the main takeaway is that the baseline definition of serum creatinine might not explain the increased risk of death.

“The increased risk of death associated with an abrupt rise in inpatient SCr depends neither on the definition of baseline SCr nor patients′ SCr trajectory before hospitalization,” the authors wrote. “Preadmission SCr‐median value may be the least biased estimate of the baseline renal function.”

The study, “Definition Of Baseline Renal Function In Hospitalized Patients With Multiple Preadmission Measures Of Serum Creatinine ‐ A Joint Modeling Approach,” was published online in Nephrology.