Physicians need to provide detailed, specific clinical documentation to ensure accurately coded claims. Coding staff in medical billing companies use clinical documentation to assign the correct codes to convey illness severity, complexity of care, and overall use of resources for the patient’s admission. In fact, in addition to impacting most quality and performance measures, these factors determine reimbursement and pay-for-performance metrics. Knowledgeable about coding rules, expert coders will thoroughly review clinical documentation and the entire medical record to identify/clarify the diagnoses and ensure accurate ICD-10 coding.

‘Principal’, ‘Primary’ and ‘Secondary’ Diagnoses

      • Principal diagnosis: The principal diagnosis for coding and billing purposes is defined as the condition established “after study” to have been primarily responsible for prompting the hospital admission (ACP Hospitalist). The signs and symptoms of the condition must have been present on admission and must have been the primary reason for admission.Suppose a patient is admitted for pneumonia and has a hemorrhagic stroke 2 days after admission. The principal diagnosis should be pneumonia, regardless of the length of time that the patient remains in the hospital or the resources that go into managing the stroke.
      • Primary diagnosis: The primary diagnosis is the most serious and/or resource-intensive diagnosis during the hospitalization or the inpatient encounter. While the primary diagnosis and the principal diagnosis are usually the same, this is not always necessary.
      • The following example from HCPro illustrates the difference between principal and primary diagnosis:

        A patient is admitted for a total knee replacement for osteoarthritis. When brought to pre-operative holding area to prepare for surgery, the patient suffers a ST-segment elevation myocardial infarction (STEMI) before the surgery begins. The patient is taken the cath lab for a stent placement instead of to operating room for the knee replacement.

        In this scenario, the principal diagnosis would be the osteoarthritis. This is the diagnosis that brought the patient to the hospital and the diagnosis which led to the admission. The STEMI is the primary diagnosis as it is the diagnosis that led to the majority of resource use.

      • Secondary diagnosis: In the CMS Official Guidelines for Coding and Reporting (OCG), “Other diagnoses” is interpreted as additional conditions that affect patient care in terms of requiring 1 or more of the following:
        • Evaluation
        • Treatment
        • Diagnostic procedure
        • Increased nursing care or monitoring
        • Extended length of stay

According to the Uniform Hospital Discharge Data Set (UHDDS), “Secondary diagnoses are “conditions that coexist at the time of admission, that develop subsequently, or that affect the treatment received and/or length of stay. Diagnoses that relate to an earlier episode which have no bearing on the current inpatient admission should be excluded”.

Identifying and Reporting Secondary Diagnoses

It is up to the coder to identify the secondary or additional diagnoses. ICD-10 guidelines state that the entire medical record should be thoroughly reviewed to determine the specific reason for the encounter and the conditions treated. Both over-reporting and under-reporting can pave the way for audits. Before assigning a code for a secondary diagnosis, coders need to consider whether the condition meets any of the above-listed elements that impact patient care.

Here are some key considerations for accurately reporting secondary diagnoses:

      • Check if documentation supports the diagnoses: The physician’s documentation should support assignment of the diagnosis to meet the reporting guidelines. If documentation supports code assignment, check if the diagnosis meets the reporting criteria for a secondary diagnosis.
      • Report diagnosis codes associated with chronic conditions that affect treatment choices: A condition that is not addressed at the encounter can be coded as long as the condition is active and affects overall patient care treatment or management. Many chronic conditions meet these criteria, though they do not necessarily directly support medical necessity of the evaluation and management (E/M) code or other codes reported for the encounter (www.aafp.com). Several “personal history of” or “family history of” conditions fall into this category. ICD-10 Guidelines make allowances for this:

“Code all documented conditions that coexist at the time of the encounter/visit, and require or affect patient care treatment or management. Do not code conditions that were previously treated and no longer exist. However, history codes (categories Z80-Z87) may be used as secondary codes if the historical condition or family history has an impact on current care or influences treatment”.

    • Consider relevancy: According to an ICD-10 Monitor report, the key consideration to determine a secondary diagnosis is relevancy, which means that the consideration of the condition is pertinent to the encounter. Examples of conditions that are relevant as secondary diagnosis though they may not be actively under treatment, according to the author, include: history of malignancy, long-term use of hormonal contraceptives (affects choice of antibiotic), GERD (gastroesophageal reflux disease) (on no medications, but may inform provider’s decision about other medications), pregnancy, alcohol dependence in remission, and psychiatric or neurologic conditions without effective medication or treatment. The existence of these conditions increases the complexity of the patient.

Knowledgeable about the ICD-10 guidelines for reporting additional diagnosis, experienced coders in medical billing and coding companies will code only the conditions that have a bearing on the current encounter. If the clinical documentation is not obvious as to whether a condition is appropriate to capture as a secondary diagnosis, the coder may require more information. Expert coders will query the physician if the documentation includes clinical indicators that justify a more specified or definitive diagnosis.