ICD-10 Series: Section 1. C.1. Certain Infections and Parasitic Diseases

In the previous blog, we discussed general coding guidelines. In this blog, we will review chapter-specific coding guideline beginning with chapter 1; Certain Infections and Parasitic Diseases which ranges from code A00 to B99. This chapter deals with ICD-10 CM coding guidelines for Certain Infectious and Parasitic Diseases generally recognized as transmissible or communicable to other people such as HIV, sepsis, severe sepsis, septic shock.

Let’s begin with ICD-10 CM guidelines for HIV/AIDS. HIV is found in the body fluids of an infected person and can be transmitted from one person to another through blood-to-blood and/or sexual contact. Coding for HIV/AIDS can be tricky depending upon if the patient is infected (asymptomatic) or if the patient has an HIV-related illness or history of an HIV-related illness. Only confirmed cases of HIV infection/illness can be coded. This is an exception to the hospital inpatient guideline Section II, H. In this context, “confirmation” does not require documentation of positive serology or culture for HIV; the provider’s diagnostic statement that the patient is HIV positive, or has an HIV-related illness is sufficient. The correct selection and sequencing of the HIV codes depend on the reason for the visit. For example,

1. When the patient is admitted for an HIV-related condition, the principal diagnosis should be B20 - Human immunodeficiency virus disease followed by additional diagnosis codes for all reported HIV-related conditions.
2. When the patient with HIV disease is admitted for an unrelated condition (such as a traumatic injury), the code for the unrelated condition should be the principal diagnosis. Other diagnoses would be B20 followed by additional diagnosis codes for all reported HIV-related conditions.
3. It is important to note that ICD-10-CM guidelines state the sequencing is irrelevant if the patient is newly diagnosed or has previous admissions/encounters for HIV-related conditions.
4. Code Z21 - Asymptomatic human immunodeficiency virus infection status, should be coded when the patient is without any documentation of symptoms and is listed as being “HIV positive,” “known HIV,” “HIV test positive,” or similar such terminology. The coder should not use this code if the term “AIDS” is used or if the patient is treated for any HIV-related illness or is described as having any condition(s) resulting from his/her HIV positive status. ICD-10-CM guidelines instruct us to use B20 instead.

Patients with inconclusive HIV serology, but no definitive diagnosis or manifestations of the illness, may be assigned code R75 - Inconclusive laboratory evidence of human immunodeficiency virus [HIV]. However, if the patient had any known prior diagnosis of an HIV-related illness, code B20 should be used. Once a patient has developed HIV-related illness, the patient should always be assigned code B20 on every subsequent admission/encounter. Patients previously diagnosed with any HIV illness (B20) should never be assigned to R75 or Z21, Asymptomatic HIV infection status.

Lets’ move on and discuss how to code for infectious agents which are classified in other chapters of the ICD-10-CM book. As coders, we have been training to include an additional code to identify the infectious agent, but often do not take the time to review the entire patient record to identify the cause of the infection.  While codes from category B95-B97 are supplemental codes they are important to include on the claim and should be utilized to identify the specific infectious agent in diseases classified elsewhere. Adding these codes strengthen the medical necessity of the services being provided. When we see documentation of an infectious disease, we should review the ICD-10-CM codebook for an instructional note advising that an additional organism code is required. For example, a patient with an unspecified UTI should be coded with N39.0 + a code from B95-B97 when the documentation indicates the infectious agent.

N39.0 - Urinary tract infection, site not specified

Excludes 1: candidiasis of urinary tract (B37.4-) neonatal urinary tract infection (P39.3) urinary tract infection of the specified site, such as:

• cystitis (N30.-)
• urethritis (N34.-)
• Use additional code (B95-B97), to identify the infectious agent.

Keep in mind we should not assign codes from lab results alone. If a finding such as an infectious agent is identified in the lab results without physician documentation, a coder should ask the physician whether the corresponding diagnosis should be added.

Lastly, let’s review proper coding for sepsis. When the documentation includes a diagnosis of sepsis, we should assign the appropriate code for the underlying systemic infection first. If the type of infection or causal organism is not further specified, assign code A41.9 - Sepsis, unspecified organism. A code from subcategory R65.2 - Severe sepsis, should only be assigned if the documentation shows evidence of severe sepsis or an associated acute organ dysfunction such as kidney failure. If a patient has sepsis and acute organ dysfunction or failure, but the medical record documentation indicates that the acute organ dysfunction is related to a medical condition other than the sepsis, do not assign a code from subcategory R65.2 - Severe Sepsis. An acute organ dysfunction must be associated with the sepsis in order to assign the severe sepsis code. If the documentation is not clear as to whether acute organ dysfunction is related to the sepsis or another medical condition, you should query the provider.

The coding of severe sepsis requires a minimum of 2 codes: first code for the underlying systemic infection, followed by a code from subcategory R65.2 - Severe Sepsis. If the causal organism is not documented, assign code A41.9, Sepsis, unspecified organism, for the infection. Additional code(s) for the associated acute organ dysfunction is also required. Due to the complex nature of severe sepsis, some cases may require querying the provider prior to assignment of the codes. For example:

A patient with an AKI develops severe sepsis due to E. coli without septic shock should be coded as:

• A41.51
• R65.2
• N17.9

For cases of septic shock, the code for the systemic infection should be sequenced first, followed by code R65.21, Severe sepsis with septic shock or code T81.12, Postprocedural septic shock. Any additional codes for the other acute organ dysfunctions should also be assigned. As noted in the sequencing instructions in the Tabular List, the code for septic shock cannot be assigned as a principal diagnosis.

The sequencing of diagnosis codes is dependent upon the patient’s presenting condition and principal diagnosis. I recommend referencing your ICD-10-CM guidelines to ensure the accuracy of coding. These guideline state:

1. If severe sepsis is present on admission and meets the definition of principal diagnosis, the underlying systemic infection should be assigned as principal diagnosis followed by the appropriate code from subcategory R65.2 as required by the sequencing rules in the Tabular List. A code from subcategory R65.2 can never be assigned as a principal diagnosis. When severe sepsis develops during an encounter (it was not present on admission), the underlying systemic infection and the appropriate code from subcategory R65.2 should be assigned as secondary diagnoses.
2. If the reason for admission is both sepsis or severe sepsis and a localized infection, such as pneumonia or cellulitis, a code(s) for the underlying systemic infection should be assigned first and the code for the localized infection should be assigned as a secondary diagnosis. If the patient has severe sepsis, a code from subcategory R65.2 should also be assigned as a secondary diagnosis. If the patient is admitted with a localized infection, such as pneumonia, and sepsis/severe sepsis doesn’t develop until after admission, the localized infection should be assigned first, followed by the appropriate sepsis/severe sepsis codes

MRSA is a common infection and is contracted by touching objects with the bacteria on them. About 2% of the population (2 in every 100 people) carry the MRSA bacteria. MRSA is often the cause of skin infections and is resistant to many antibiotics. If left untreated, MRSA infections can become severe and cause sepsis.

When a patient is diagnosed with an infection that is due to methicillin-resistant Staphylococcus aureus and that infection has a combination code that includes the causal organism (e.g., sepsis, pneumonia) assign the appropriate combination code for the condition (e.g., code A41.02 - Sepsis due to Methicillin-resistant Staphylococcus aureus or code J15.212 - Pneumonia due to Methicillin-resistant Staphylococcus aureus). Do not assign code B95.62 - Methicillin-resistant Staphylococcus aureus infection as the cause of diseases classified elsewhere, as an additional code, because the combination code includes the type of infection and the MRSA organism. Do not assign a code from subcategory Z16.11 - Resistance to penicillin as an additional diagnosis.

When there is documentation of a current infection (e.g., wound infection, stitch abscess, urinary tract infection) due to MRSA, and that infection does not have a combination code that includes the causal organism, assign the appropriate code to identify the condition along with code B95.62, Methicillin-resistant Staphylococcus aureus infection as the cause of diseases classified elsewhere for the MRSA infection. Do not assign a code from subcategory Z16.11, Resistance to penicillin.

Coding for infections is complicated and is often miscoded which could result in a lower payment for your organization and/or physician. Remember to read through the ICD -10-CM guidelines to ensure proper coding and always query the physician when documentation is inconsistent, conflicting, incomplete or ambiguous.

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