If you had to pick a single metric to a measure a hospital, which would you choose?

Of course, you can’t boil everything about a hospital down to one, single data point. Defining quality, throughput, and other factors used to evaluate a hospital is difficult business. The Centers of Medicare & Medicaid Services (CMS) tracks dozens of core metrics related to both quality and process, both inpatients and outpatients. As a practicing ER doc, much of what I can do to improve outcomes for my patients comes down to delivering care more quickly, so it’s worth noting just how many of the CMS metrics relate to one thing: time.

The CMS website lists 36 different metrics under the category of “Timely and Effective Care,” most of which come down to providing a certain standard of care within a given time frame. Hospitals, while increasingly focused on the quality outcomes being measured by CMS, nonetheless often have a laser focus on various throughput measures, since a hospital’s ability to move volume through its facilities goes straight to the bottom line.

For hospital leaders it often comes down to a simple formula: X number of beds in the hospital, times 24 hours in a day, equals the amount of care the hospital is capable of delivering, and thus, billing for.

So while hospitals are enormous institutions with thousands of moving parts and dozens of interrelated services, sub-contractors, and physician groups all responsible for delivering on their piece of the healthcare puzzle, there is one metric that can encapsulate much of what works and what doesn’t in a hospital: emergency department length of stay for admitted patients.

It may seem counterintuitive, but measuring the length of stay in the emergency department for patients who are ultimately admitted actually provides an enormous window into a huge range of inpatient hospital processes.

Length of stay’s long reach

A huge proportion of patients in the emergency department will come into contact with other departments within the hospital, most notably lab and radiology. Patients who have a long length of stay in the ED often do so because their lab turnaround time was slow, or radiology took longer than expected. Small adjustments in improving lab turnaround times which are then multiplied out to hundreds of patients a day can have a huge impact on lowering length of stay in the emergency department.

Length of stay also encompasses a hospital’s ability to turnaround its beds, manage throughput, and maximize bed capacity. That means even the efficiency of a hospital’s laundry facilities are ultimately reflected in length of stay. If much of effective hospital capacity management comes down to efficiently admitting and discharging patients, it follows that the length of time that patients spend in the ER waiting to be admitted to the hospital is a good reflection of how well the hospital is managing the process. And in fact, the median time from the moment the admit decision is made to the time the patient leaves the emergency department is a core measure tracked by CMS.

Length of stay is also a key component in patient satisfaction scores. It’s pretty intuitive that patients are happier the less time they have to spend in the hospital. Most studies show that if you mess up patient satisfaction early on in a patient’s visit, i.e., in the emergency department, you won’t be able to fix it later on in the process, no matter how long their stay in the hospital. That means improving length of stay for patients in the emergency room will improve patient satisfaction scores for inpatients throughout the hospital. It’s pretty cool, actually.

An indication your hospital is improving

One sure way to see whether a hospital is improving or worsening is to look at the change in length of stay over time. Whether length of stay for admitted patients is 353 minutes (the average for Maryland) or 274 minutes (the average nationwide) isn’t as important (although lower is better) so much as whether the number is going up or down. Of all the important metrics a hospital could look at, this one encompasses the greatest swath of hospital processes, services, and physician groups.

And yes, Hospital Compare tracks this one as well. It’s code is ED-1b: “Median time from emergency department arrival to emergency department departure for admitted emergency department patients.”

ED-1b: Measure it, track it, improve it.

Michael Cetta is an emergency physician who blogs at The Shift.