By Cesar M Limjoco, MD
Chief Medical Officer
T-Medicus LLC
It surprises me that to this day, many people are still confused about the proper selection of principal diagnosis in an inpatient encounter. Back in 2001, I wrote “The Principles of Inpatient Coding: Principal Diagnosis (PDX) and Other Diagnosis (ODX)1.” But, through the years questions and disputes still keep popping up. This article revisits the issue and provides additional insights to the original article.
There are a ton of PDX guidelines, but it can all be simplified to one statement…
When you know your WHY, you’ll know your way. – Simon Sinek [@simonsinek]
WHY was the patient admitted to acute inpatient care? Does the patient need to be admitted to acute inpatient care or can the patient’s condition be managed as an outpatient (including rehabilitation, assisted living or nursing home) or at home (with or without home care, or even hospice)? This is crucial because all the data and case studies have consistently shown that the risks outweigh the advantages of inpatient care when the patient can be treated outside of the acute inpatient care space. Thus, the provider needs to mitigate the need for it. It is of utmost importance to understand that the answers to the above questions rest on a valid principal diagnosis (PDX). If the documented narrative is nebulous about the circumstances of admission, it creates uncertainty on the need for the level of care and opens the encounter to payor denial. The 2017 US Medicare national improper payment report pegged $6.3B to lack of medical necessity for inpatient acute care2. Recent news headlined a healthcare system’s $18M settlement due to Medicare patients that could have been treated as outpatients. A coherent principal diagnosis clarifies what occasioned the admission and makes it easy to validate the medical necessity for an admission to acute inpatient care.
There are times that social and economic reasons preempt proper care at home or as an outpatient. Third party payors do not pay for social and economic predicaments; but, reality may dictate the need to keep the patient in the hospital. Insurance will not cover the stay and the patient has to assume financial responsibility. If the patient is unable, the hospital then eats up the cost. These are no-win situations that Population Health needs to tackle.
The Principal Diagnosis refers to the condition established after study to be chiefly responsible for occasioning the patient’s admission to the hospital for care3. The selection of principal diagnosis is determined by the circumstances of admission, diagnostic workup and/or therapy provided4. The principal diagnosis is the definitive diagnosis arrived after study to have caused the admission. It may take a day or two or even the whole stay to arrive at it or its most probable etiology. Sometimes, it may remain unknown and the principal diagnosis then falls back to the symptom/manifestation. When this happens, medical necessity becomes harder to justify, unless there are mitigating circumstances that support the need for inpatient admission.
One major misconception in the selection of principal diagnosis is that it is the reason the patient presents to the hospital. The patient’s chief complaint upon presenting to the ED may not necessarily satisfy the need for acute inpatient care. If the condition can be managed appropriately as an outpatient or at home, the patient does not need to be admitted to inpatient care. When it is unsure what the patient has or that the risk of discharging home is high, the patient can be monitored for a period of a few hours up to 24-48 hours as an outpatient observation. Once the patient is cleared of danger, the patient can then be discharged. If the underlying issue(s) need(s) a higher level of intervention, the patient can be admitted to acute inpatient care at any time.
So, a patient may come in for a condition that may not need acute inpatient care; but upon evaluation, the provider discovers a more serious problem that compels the admission. This acute condition that the patient did not think was an issue, but was discovered by the provider, may now satisfy the definition of principal diagnosis and also substantiate inpatient care. Or, a patient may come in for an acute condition that may not need acute inpatient care, but because of concurrent chronic comorbidities; there is the need for a higher level of care. This scenario, where there is a combination of factors that preclude discharge within 24-48 hours, may justify the need for inpatient care. The acute condition will always trump the chronic condition(s) as principal diagnosis. Chronic conditions only become the principal diagnosis (in the absence of an acute condition that need acute inpatient care) when it is the indication for an inpatient procedure and when coding convention, i.e., “code first” rule says otherwise.
Another ED scenario is — a patient presents with a benign complaint that didn’t need inpatient admission. While in the ED, develops an acute condition that now necessitates inpatient care. This condition was not what brought the patient to the hospital but had developed while the patient was in the ED. For example, a patient presents with epistaxis. It was managed effectively and now the patient is being observed and will be discharged shortly. The patient suddenly develops chest pains from an acute myocardial infarction. The epistaxis brought the patient to the ED. The MI occasioned the admission to inpatient care.
The question that many would be thinking at this point would be, what if the patient has two or more acute conditions that satisfy the need for an admission. This is where the co-equal principle on principal diagnosis selection applies – the hospital (and in inference, the coder) may choose which of the conditions has higher severity that consumed more hospital resources and thus carry an appropriately higher reimbursement. The acute conditions may even be inter-related or have a causal relationship; e.g., patient comes in with Acute Respiratory Failure due to Acute-on-chronic Systolic Left Ventricular Failure. “When two or more diagnoses equally meet the criteria for principal diagnosis as determined by the circumstances of admission, diagnostic work-up, and/or therapy provided (and the Alphabetic Index, Tabular List, or another coding guideline does not provide sequencing direction), any one of the diagnoses may be sequenced first5.” The provider can provide documentation of the circumstances for the basis for coequality of the conditions. The coder can then apply the Diagnosis Related Groups (DRG) algorithm to discern which of the conditions carry a higher severity weight. In these scenarios, it would be groundless to ask the provider to choose which, among a number of conditions, necessitated the admission. DRGs are outside most providers’ purview.
For example, a patient presents with multiple problems: shortness of breath, fever, and chest pain. Chest x-ray demonstrates an exacerbated CHF, examination reveals acute bronchitis, and prior history and current EKG findings are consistent with unstable angina (cardiac enzymes were negative). The three conditions were treated with medications. All three diagnoses equally meet the criteria for the definition of principal diagnosis and the hospital can sequence any one as the principal diagnosis. It needs to be said that, the aforementioned conditions individually may not satisfy medical necessity for an inpatient admission. But, other factors come into play that may require a higher level of care.
But let’s say the above patient undergoes coronary arteriography revealing coronary artery disease (CAD) with 85-90% blockage of two prominent branches and has a percutaneous transluminal coronary angioplasty (PTCA) and stent placements. In this scenario, the workup and treatment clearly establish CAD, as the underlying etiology of the patient’s unstable angina, that warranted definitive intervention and therefore is the appropriate principal diagnosis. Unstable angina here is a symptom of the coronary artery disease. Just an FYI, unstable angina can also be caused by other conditions that induce ischemia to the myocardium, e.g., aortic valvular stenosis, cardiomyopathy, arrhythmia as well as noncardiac (demand) causes like anemia. Definitive treatment is always directed to the pathology to fix the problem, whereas supportive treatment affords symptomatic relief at best.
The complexities of Medicine dictate the need for accurate documentation. All in all, it comes down to the narrative. When there is transparency in the documentation and the record speaks for itself, everything else falls into place and will withstand scrutiny. Documentation showing clinical support of the conditions (including onset) needs to be unimpeachable. The Clinical Truth™️ will always prevail. ‘Nuff said!
1 https://web.archive.org/web/20090109010008/http:/projects.ipro.org/index/inpatient_coding
2 https://www.cms.gov/Research-Statistics-Data-and-Systems/Monitoring-Programs/Medicare-FFS-Compliance-Programs/CERT/Downloads/2017-Medicare-FFS-Improper-Payment.pdf
3 Uniform Hospital Discharge Data Set
4 American Hospital Association’s Coding Clinic for ICD-9-CM, 1990:2Q:p.4 PDX#4,5.
5 AHA Coding Clinic, 90:2Q:p.4 PDX#5.
