Q&A: Understanding GMLOS

Q: I’ve heard that the geometric length of stay (GMLOS) is always rounded to the nearest whole number as inpatient claims are paid by day. Based on my understanding of the inpatient prospective payment system (IPPS), I thought that each inpatient stay is paid by a fixed amount, regardless of the number of days the patient is in the hospital. Can you clarify this for me? Also, are there any cases when the GMLOS wouldn’t be rounded to the closest whole number?

A: You’re correct that under the IPPS, each hospital encounter is paid a specific amount of money per encounter, which is calculated using the relative weight (RW) of each MS-DRG (no matter where you work, the RW for each MS-DRG will be the same). The relative weight is then multiplied by the hospital’s base rate (which varies from facility to facility; the national base rate for 2019 is $5568.00). This is a simplified answer as other things are taken into consideration when determining a hospital’s reimbursement for an inpatient stay, such as how the facility performs on certain quality programs, and whether they’re a teaching hospital.

As for your question regarding payment by days or episode of care, let’s look at an example. Let’s assume that, based on the documentation, the patient had a principal diagnosis that led to the assignment of MS-DRG 179, Respiratory infection and inflammation without a CC/MCC. This MS-DRG has a RW of 0.9215. Multiplied by the base rate, that gives us a total reimbursement of $5130.91 with a GMLOS of 3.2 days.

Based from other calculations, I know that the average length of stay for this type of patient is somewhere around four days, so the hospital would receive approximately $1,282.72 per day to cover all hospital-associated costs excluding physician payment.

If the patient goes home in less than four days, stays longer than the average four days, or is transferred to another facility, then the reimbursement would change. The hospital could cover their cost or lose money based on a patient’s length of stay and what tests are performed or what care is provided during the patient’s stay.

I want to stress that much more goes into these calculations to determine how much a facility would be paid then simply what is covered in this example. As a CDI specialist, you will establish the “working” MS-DRG for a patient. This working MS-DRG will give you the GMLOS. This GMLOS is generally what the CDI specialist will use to determine their review schedule for the patient’s medical record.

For example, I know if a person has a four-day LOS, I can probably wait 24-48 hours to do my initial review, giving the physician a chance to evaluate any testing the patient may have undergone. If the patient only has a three or fewer days expected LOS, I know I need to perform my initial review sooner.

Knowing the LOS for an encounter would also trigger a CDI specialist to question when a person is not discharged when expected, which could indicate that a follow-up review is necessary. 

Remember, a CDI specialist’s job is to make sure the documentation is present in the medical record to support the appropriate principal diagnosis assignment, secondary diagnoses, and any procedures performed during the patient’s stay. Accurate documentation will lead to an appropriately assigned MS-DRG, which will include the appropriate expected LOS for that patient.

I am also including an answer from CDI Education Specialist Allen Frady, RN-BSN, CCDS, CCS, CRC, regarding LOS:

We often explain that the geometric mean excludes outliers but that is the oversimplified definition. They don’t actually chop off outliers; it’s just that a geometric mean is less sensitive to outliers than the average due to the math being done differently.

Average LOS (ALOS) equals the sum of LOSs divided by the number of stays:

Two stays, one that is four days and one that is 12 days long, gives you 16 days, divided by the two stays so you get 16/8 =  8 as the ALOS

The geometric of that same example would be four days multiplied by 12 days and then take the square root so you’d get the square root of 48 which is 6.928 days.

Editor’s Note: Sharme Brodie, RN, CCDS, CDI education specialist and CDI Boot Camp instructor for HCPro in Middleton, Massachusetts, answered this question. For information, contact her at sbrodie@hcpro.com. For information regarding CDI Boot Camps, click here.