Hospitals use observation status because Medicare rules require doctors to expect a patient will need hospital care crossing two midnights before classifying them as an admitted inpatient. If a physician believes you’ll need less than two midnights of care, the hospital is required to treat you as an outpatient under observation, even if you’re in a hospital bed, wearing a gown, and staying overnight. This distinction exists primarily as a billing classification, but it carries real financial consequences for patients.
The Two-Midnight Rule
The core driver behind observation status is a Medicare regulation known as the Two-Midnight Rule. Under this rule, a physician must expect that a patient will require hospital care spanning at least two midnights for the stay to qualify as an inpatient admission paid under Medicare Part A. That expectation has to be based on documented clinical factors: the patient’s medical history, existing conditions, severity of symptoms, and risk of something going wrong. If the medical record doesn’t support the expectation of a two-midnight stay, the hospital can’t bill Medicare for inpatient care.
When a doctor expects your stay will be shorter than two midnights, you’re placed in observation. You receive treatment, monitoring, and testing, but you’re technically classified as an outpatient the entire time. There is a narrow exception: physicians can admit patients for shorter stays if their clinical judgment supports it, but they must thoroughly document why inpatient care was necessary. Most hospitals treat this exception cautiously.
Why Hospitals Are Cautious About Admitting
Hospitals face significant financial pressure to classify patients correctly. Medicare employs Recovery Audit Contractors (RACs) to review hospital billing and flag cases where patients were admitted as inpatients but, in the auditors’ view, should have been treated under observation. A study of three academic medical centers found that RACs audited 8% of all inpatient Medicare encounters and alleged overpayment in nearly a third of those reviewed cases. Notably, none of the auditors contested whether the patient actually needed the care they received. The disputes were entirely about whether the care should have been billed as inpatient or outpatient.
When a hospital loses one of these audits, it must repay Medicare the difference between the higher inpatient rate and the lower outpatient rate. Appealing takes a long time, averaging about 555 days per case. Nearly half of disputed cases in the study were withdrawn by hospitals and rebilled under the lower outpatient rate simply to avoid the drawn-out appeals process. This dynamic pushes hospitals to err on the side of observation status whenever a case is borderline.
How Hospitals Decide Your Status
Most hospitals use commercial screening tools to help physicians determine whether a patient meets inpatient or observation criteria. One widely used system, called InterQual, applies branching logic based on specific clinical findings. For a patient who fainted, for example, the tool checks for factors like a weak heart pump, a family history of sudden death, symptoms such as shortness of breath or fainting during physical activity, and specific abnormalities on a heart rhythm test. A patient needs to meet criteria across multiple categories to qualify for inpatient admission. If they don’t check enough boxes, the tool recommends observation.
These tools serve as guidelines, not mandates. The admitting physician still makes the final call, but disagreeing with the screening tool creates audit risk. Hospitals often employ utilization review teams that monitor cases in real time, sometimes switching a patient’s status from inpatient to observation (or vice versa) during the stay as the clinical picture changes.
How Observation Status Costs You More
The financial difference between inpatient and observation can be substantial. Inpatient stays are covered under Medicare Part A, which has a single deductible per benefit period. Observation stays are covered under Part B, which bills each service separately with its own copayment. While the copayment for any single outpatient service is capped at the inpatient deductible amount, your total copayments across all outpatient services during the stay can exceed that cap. A 2012 analysis found that privately insured patients receiving observation and other outpatient hospital services paid about four times as much out of pocket as admitted patients, averaging $199 versus $47.
Routine medications create another cost problem. If you’re an inpatient, the hospital provides your regular medications (blood pressure pills, diabetes drugs, and so on) as part of your stay, covered under Part A. Under observation status, Medicare Part B generally does not cover these “self-administered drugs.” The hospital may still give them to you, but it can bill you directly. Your Part D drug plan might reimburse some of that cost, but most hospital pharmacies don’t participate in Part D networks, so you may need to pay upfront and submit a claim for a partial refund later. If the drug isn’t on your plan’s formulary, you pay the full hospital price.
The Skilled Nursing Facility Problem
Perhaps the most consequential impact of observation status involves what happens after you leave the hospital. Medicare requires three consecutive days as a formally admitted inpatient before it will cover a stay in a skilled nursing facility. Time spent under observation does not count toward those three days, even if you were in a hospital bed for a week. A patient could spend four days in the hospital under observation, need rehabilitation afterward, and have zero qualifying inpatient days for nursing home coverage.
This rule applies specifically to traditional Medicare. Private insurance policies generally do not impose a three-day inpatient requirement. Cigna, Aetna, and most other commercial plans base nursing home coverage on whether the patient needs skilled care, regardless of whether the hospital stay was inpatient or observation. Even Medicare Advantage plans, the private alternatives to traditional Medicare, have largely dropped this barrier. As of recent data, 95% of Medicare Advantage plans waive the three-day inpatient stay requirement for skilled nursing coverage.
Your Right to Be Notified
If you’re on Medicare and placed in observation, the hospital is legally required to give you a written notice called the Medicare Outpatient Observation Notice, or MOON. This form explains that you are an outpatient receiving observation services, describes how this affects your costs, and notes the implications for skilled nursing facility coverage. The hospital must deliver this notice no later than 36 hours after observation services begin, or sooner if you’re discharged before that point.
Receiving this notice is your signal to ask questions. You can ask your doctor whether your condition might qualify for inpatient admission, and you can request that the hospital’s case management team review your status. If you believe observation status was applied incorrectly, you have the right to appeal through Medicare after discharge. The MOON itself includes information about how to get help understanding your rights.
What You Can Do
If you or a family member is hospitalized, ask directly whether the stay is classified as inpatient or observation. Don’t assume that being in a hospital bed with an IV means you’ve been admitted. Request the status in writing if it isn’t clear. If you’re under observation and your condition worsens or your stay extends beyond what was initially expected, ask whether your status should be reconsidered. Hospitals can and do convert observation stays to inpatient admissions when the clinical picture changes.
For people on traditional Medicare who anticipate needing nursing home care after a hospital stay, the classification matters enormously. Tracking your inpatient days carefully, and understanding that observation days don’t count, can help you plan ahead and avoid unexpected bills that can run into tens of thousands of dollars for uncovered skilled nursing care.