Understanding the Clinical Diagnosis of Sepsis-3

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Original story posted on: November 5, 2018

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Lack of a SOFA score change does not rule out sepsis.

A couple weeks ago, I spoke about how the current definition of sepsis, known as "sepsis-3," was the best definition for the medical community to use at this time. This week, I'm going to discuss the clinical diagnosis of sepsis.

Sepsis diagnoses are a frequent source of disagreement between providers and payers . I'm not advocating for the capture of more or fewer sepsis diagnoses, but rather for correct sepsis diagnoses. Sepsis diagnoses impact not only a provider's DRG-based payments, but also government subsidies to insurers who offer Medicare Advantage and Patient Protection and Affordable Care Act (PPACA) exchange plans. The same definition needs to be applied consistently and correctly by all.

The sepsis-3 definition is "life-threatening organ dysfunction caused by a dysregulated host response to infection." What about the Sequential Organ Failure Assessment (SOFA) score? Isn't that also the definition of sepsis-3? No, it is not.

A myth I want to dispel is that SOFA criteria must be met in order to diagnose sepsis; that is not true. If a clinician feels that a patient has life-threatening organ dysfunction caused by a dysregulated host response to infection, based on a reasonable clinical assessment, then that patient has sepsis.

Arguing that a patient is not septic because the SOFA score did not change by two points is putting the cart before the horse.

The sepsis-3 authors would have liked to have developed a new and validated organ dysfunction tool to accompany the sepsis-3 definition, but there was neither the time nor resources to do so. However, they recognized that some clinical criteria would have to be put forth to assist in the diagnosis of sepsis.

They actually studied three different tools to identify the organ dysfunction in the new sepsis definition: the aforementioned SOFA, the Logistic Organ Dysfunction System (LODS), and the Systemic Inflammatory Response Syndrome (SIRS). SOFA and LODS both performed better than SIRS. Because SOFA is easier to administer than LODS, the SOFA score was chosen. That's the only reason. So let's take a closer look at SOFA.

The SOFA score was created in 1996 by one of the sepsis-3 authors, Dr. Jean-Louis Vincent. It looks for markers of dysfunction in one of six functional organs or organ systems: respiration, coagulation, liver, cardiovascular, central nervous system, and renal. Specific inputs include the P/F ratio (a measure of hypoxemia), platelet count, bilirubin level, mean arterial pressure or use of vasopressors, Glasgow Coma Scale, creatinine level, and urine output. Points are assigned to each organ system, and the points are simply added. A change of two points over baseline is indicative of significant organ dysfunction. If the baseline score is not known, it is presumed to be zero.

Several specific questions arise with the practical application of the SOFA inputs. To determine a P/F oxygen ratio, technically, an arterial blood gas (ABG) is required. If an ABG is not obtained, does that mean the input cannot be scored? No, because the relationship between oxygen pressure and oxygen saturation, as well as the relationship between inspired oxygen and various oxygen delivery devices, is quite well-established.

When inferring a partial pressure of oxygen and fraction of inspired oxygen provided, however, it is wise to be conservative in estimates when there can be no reasonable doubt that the P/F ratio is below 300. Regarding the Glasgow Coma Scale, the three component inputs may not all be documented, but an abnormal result in one input can guarantee that the score cannot be higher than a certain number. The most conservative (highest) number should be used.

What if the organ that has experienced dysfunction is also the source of infection, such as pneumonia causing hypoxemia? According to a sepsis-3 lead author, the panel discussed this, and determined that the organ system should still be included. For practicality, SOFA inputs should be taken from the same 24-hour period to avoid confounding by time.

In summary, SOFA is a tool that can be used to help support the diagnosis of sepsis, but lack of a SOFA score change does not rule out sepsis. Calculating the proper SOFA score can be challenging but remember that the clinician is the person who should make the final diagnosis of sepsis, not an auditor sitting on a sofa.

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Edward Hu, MD, CHCQM-PHYADV

Edward Hu, MD CHCQM-PHYADV is a board-certified internist and is the current president of the American College of Physician Advisors (ACPA). Dr. Hu is executive director of Inpatient Physician Advisor Services for the University of North Carolina Health Care System. Opinions expressed are his own and not representative of ACPA or UNC.

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