ICD-10 Code A91: Dengue hemorrhagic fever

Key Takeaways

ICD-10 Code A91 is the billable ICD-10-CM diagnosis code for dengue hemorrhagic fever, valid from 2016 through the 2026 code set.

A91 sits under category A90-A99 (Arthropod-borne viral fevers) within chapter A00-B99 (Certain infectious and parasitic diseases).

A91 codes the hemorrhagic form only; classical dengue fever uses the separate code A90 – mixing the two is one of the most common documentation errors.

Pabau’s claims management software and digital clinical forms help infectious disease and travel medicine clinics document A91 encounters accurately for cleaner claim submission.

ICD-10 Code A91: Definition and clinical description

ICD-10 Code A91 is the billable ICD-10-CM diagnosis code for dengue hemorrhagic fever. Maintained jointly by the Centers for Medicare and Medicaid Services (CMS) and the National Center for Health Statistics (NCHS), it has been valid and in use in every annual ICD-10-CM edition from 2016 through 2026.

Dengue hemorrhagic fever is a serious condition caused by dengue virus infection. Patients typically present with an acute febrile illness followed by restlessness, irritability, and bleeding. Importantly, the hemorrhagic form is clearly distinct from classical dengue fever: plasma leakage, thrombocytopenia, and evidence of bleeding are the key signs that separate an A91 encounter from a straightforward A90 code. As a result, accurate use of ICD-10 Code A91 starts with recognising that distinction before the chart is closed.

Specifically, this reference covers the code’s classification structure, billable status, the A90-versus-A91 distinction, documentation requirements, ICD-9-CM crosswalk, related codes, and the most common coding errors clinicians and medical coders encounter with ICD-10 Code A91.

Billable status and ICD-10-CM classification hierarchy

A91 is a billable/specific code. That means it can be used directly on insurance claims and for billing purposes without any further breakdown. Consequently, no additional characters are added to the base code.

The full classification structure for ICD-10 Code A91 reads as follows. For accurate hemorrhagic condition coding, understanding where a code sits within the chapter structure is essential for code ordering decisions. Moreover, this context informs how payers read the claim.

The WHO ICD-10 browser places A91 within the same A90-A99 block alongside other mosquito- and arthropod-borne viral fevers including Chikungunya (A92.0), West Nile virus (A92.3), and Zika virus (A92.5). This matters when a patient presents with fever of unknown cause in a travel medicine setting: coders must select the most specific code supported by physician documentation rather than a default within the block.

A90 vs A91: How ICD-10 Code A91 differs from classical dengue

Confusing A90 and A91 is the most common coding error in dengue-related encounters. Both codes appear in the same block, and many electronic health record systems default to A90 when the coder searches “dengue fever” without a modifier. For that reason, here is why the distinction matters clinically and for billing.

• A90 (Dengue fever, classical dengue): An acute, rash-causing febrile illness caused by one of four dengue virus serotypes. Spread by Aedes aegypti mosquito bite. Presents with high fever, severe headache, muscle pain, and rash. No plasma leakage or significant bleeding.
• A91 (Dengue hemorrhagic fever): The more severe form. Defined by the WHO as meeting all four criteria: fever, bleeding signs, thrombocytopenia (platelet count 100,000/mm³ or below), and evidence of plasma leakage (haematocrit rise of 20% or more, or pleural effusion/ascites).

Dengue shock syndrome, the most severe presentation on the dengue spectrum, falls within the dengue hemorrhagic fever category and is correctly reported with A91. Notably, there is no separate ICD-10-CM code for dengue shock syndrome; the physician’s note about shock in the context of dengue hemorrhagic fever supports the A91 assignment alongside an applicable septic shock or circulatory collapse code where documented. For a broader look at how ICD-10 diagnostic codes are built across different clinical conditions, the CDC/NCHS tabular framework applies consistently across all chapters.

ICD-10 Code A91 chart section: quick reference

The table below summarises the key coding attributes for A91 that coders and billers need at a glance. For ICD-10-CM diagnostic codes across all specialties, the same attribute structure applies.

Documentation requirements for ICD-10 Code A91

A91 requires documentation that goes beyond a positive dengue serology result. Specifically, the physician’s note must clearly support the hemorrhagic form. If one element is missing, the coder cannot assign A91; as a result, the encounter reverts to A90 (or, if neither is confirmed, an unspecified fever code), which understates the clinical severity and may affect payment for higher-acuity management.

The CDC/NCHS ICD-10-CM tool provides the tabular list and official guidelines that set these documentation standards. For A91 specifically, the record should include all of the following to support the code:

• Confirmed fever: Documented febrile illness, typically 2-7 days in duration.
• Hemorrhagic manifestations: At minimum a positive tourniquet test, petechiae, ecchymosis, purpura, or bleeding from the mucosa, gut, injection sites, or other locations.
• Thrombocytopenia: Platelet count at or below 100,000/mm³, supported by a dated laboratory result in the chart.
• Plasma leakage evidence: A haematocrit rise of 20% above baseline, or clinical or imaging evidence of pleural effusion, ascites, or low blood protein.
• Dengue confirmation: Positive NS1 antigen, IgM serology, or PCR result with the collection date and sample type recorded.

Travel history is not a coding criterion but is strongly recommended in the note to satisfy medical necessity review, particularly for US-based infectious disease and travel medicine clinics where dengue is a travel-acquired diagnosis. In addition, proper patient record documentation at the point of care removes the need for historical chart changes that can delay claim resolution.

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Coding guidelines and sequencing notes for A91

Under the ICD-10-CM Official Guidelines for Coding and Reporting, A91 is listed as the principal diagnosis when dengue hemorrhagic fever is the reason for the encounter or admission. In addition, secondary diagnoses for complications including thrombocytopenia, encephalitis, or organ damage are coded where documented and clinically significant.

Two sequencing scenarios, however, generate the most coder questions. Review this reference for procedure code documentation that applies alongside the diagnostic code in complex encounters.

• Suspected dengue, not yet confirmed: During the admission workup, code the presenting signs and symptoms (fever, thrombocytopenia, rash) rather than A91 until the diagnosis is confirmed. The ICD-10-CM guidelines allow coding “uncertain” diagnoses for inpatient encounters once the attending documents the condition as such at discharge. For outpatient encounters, code only the confirmed diagnosis or presenting symptom.
• Dengue shock syndrome: A91 is the correct code. Assign an additional code for septic shock (R65.21) or circulatory collapse if separately documented and clinically supported. Do not assign a separate hemorrhagic fever code — A91 covers this presentation.

ICD-9-CM crosswalk and historical context for A91

Before the US switch to ICD-10-CM in October 2015, dengue fever in both its classical and hemorrhagic forms was reported under a single ICD-9-CM code: 061 (Dengue fever). As a result, the move to ICD-10-CM introduced the A90/A91 split, giving coders the ability to capture the clinical difference between the two presentations for the first time in the US coding system.

This matters for practices reviewing historical claims data, quality metrics, or disease tracking records. Specifically, any pre-2015 dengue encounter coded as 061 cannot be assumed to have been the hemorrhagic form. Therefore, for billing and coding workflows involving historical data, the ICD-9 crosswalk requires clinical review to determine which ICD-10-CM code the encounter actually supports. Robust billing and coding workflows that maintain searchable clinical documentation make this historical review far less burdensome.

Related codes adjacent to ICD-10 Code A91

Coders working with dengue encounters should be familiar with the codes immediately surrounding A91 in the A90-A99 block, as well as relevant complication codes assigned alongside it. In particular, for practices managing integrative medicine practice software that handles a broad range of infectious and vector-borne diagnoses, understanding the adjacent code landscape prevents inadvertent mis-selection.

Pabau and clinical documentation for infectious disease coding

Accurate use of ICD-10 Code A91 depends entirely on having the right clinical criteria in the record at the time of coding. Consequently, practices using claims management software that connects directly with clinical documentation can close the gap between what the physician captures and what reaches the billing queue.

Pabau’s digital clinical forms allow travel medicine and infectious disease clinics to build structured intake and assessment forms that capture the exact elements needed for A91 documentation: bleeding signs, lab result fields, travel history, and platelet count cut-offs. When those fields are filled at the point of care, the coding team works from complete records rather than chasing addenda. As a result, denial rates fall and claims are resolved faster for complex dengue encounters. Finally, review clinic compliance documentation standards to ensure your infectious disease records meet both coding and regulatory requirements.

Conclusion

Dengue hemorrhagic fever cases coded without the right clinical criteria to support A91 default to A90, understating the severity and potentially triggering denials for higher-acuity management. In short, getting the distinction right requires documentation that meets the WHO’s four-criteria standard, captured at the point of care.

As a result, Pabau’s structured clinical forms and claims management software give infectious disease and travel medicine clinics the tools to assign ICD-10 Code A91 with confidence. To see how Pabau handles clinical documentation for complex infectious disease encounters, book a demo.

Continue your research

Need a reference for other hemorrhagic and vascular ICD-10 codes? Intraparenchymal hemorrhage ICD-10 codes provides a parallel coding guide for hemorrhagic diagnoses across neurological presentations.

Looking to streamline coding accuracy across your practice? Pabau claims management software integrates clinical documentation with billing workflows to reduce denials on complex diagnosis codes.

Need structured forms for infectious disease intake? Pabau digital forms let travel medicine and infectious disease clinics capture the specific clinical criteria needed for accurate ICD-10 coding at the point of care.

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