Urine Albumin:Creatinine Ratio - The Next Big Thing or an Excuse for Substituted Judgment?

The Gist:  Urine Albumin: Creatinine Ratio (ACR) is higher in the sicker septic patients compared with the less sick septic patients and may be able to predict which patients will take a turn for the worse.  This test probably won't add much to clinical care or goal directed therapy, at least in the ED at this time.  

Sepsis is kind of a big deal.  The "Surviving Sepsis" campaign championed by Dr. Rivers seems to dominate EM literature and we continuously seek tests that allow us to identify, stratify, and treat septic patients.  According to a study in American Emergency Medicine last month, patients presenting to the ED with sepsis do at least as well as those patients who are directly admitted to the hospital.  Good job.  However, we can always do better.  

As in other high-risk issues like chest pain, myocardial infarction, and pulmonary embolism, we look for a test that will allow us to pat ourselves on the back for making a decision we've already really made using clinical gestalt.  In pulmonary embolism, this may be a d-dimer or CT scan in a PERC negative/low-risk Wells patient.  Lactate, central venous pressure (CVP), and inferior vena cava (IVC) diameter are some of the parameters currently utilized to help stratify septic patients.  The urine albumin:creatinine ratio seeks to do the same.  This test is based on the fact that the kidneys tend to spill albumin during inflammatory states, a result of endothelial cell injury.  Thus, the sicker patients should spill more albumin in their urine, perhaps before they deteriorate into a state of tissue hypoxia.    

This study was published in Academic Emergency Medicine in March 2012 and is predicated on the theory that the ACR could predict which sepsis patients have more severe outcomes.  

Methods

• Convenience sample of patients meeting criteria for sepsis presenting to one of two EDs
• Pilot study - prospectively enrolled if the patient had a urinalysis done
• Patients could not have signs of tissue hypoxia or shock at the time of presentation
• Primary outcome was disposition from ED (ICU/step down, discharged home, admit to floor)

Results

• Patients admitted to more intensive medical care settings had higher levels of ACRs compared with those patients who were sent home.
• This didn't hold true for patients with a genitourinary source
• Better prognostic indicator than serum lactate levels (which were not prognostic in this cohort).
• So, patients who already ended up in the ICU or on the floor due to clinical presentation/labs had higher ACR
• Patients had a solid mean arterial pressure (MAP), with an average MAP of 89.5. 
• This patient population wasn't comprised of the super sick, although 51 of the 92 patients qualified for the title "severe sepsis."
•  Perhaps the physicians were more cognizant of the disposition they gave to their patients, indicative of a Hawthorne effect.

In the future, this test may play a role in allowing physicians to feel better about discharging a patient home or  convince an intensivist to accept a patient who might have otherwise decent labs or vitals.  It may increase our sensitivity in detecting septic patients that will deteriorate.  My best guess, however, is that it really only tells us what we already know in our clinical assessment of a patient.   

References:

Drumheller, B. C., McGrath, M., Matsuura, A. C. and Gaieski, D. F. (2012), Point-of-care Urine Albumin:Creatinine Ratio Is Associated With Outcome in Emergency Department Patients With Sepsis: A Pilot Study. Academic Emergency Medicine, 19: 259–264. doi: 10.1111/j.1553-2712.2011.01266.x