Hospital Admission Authorization (AIH): know the rules

Anyone who has been through a hospital stay has noticed the number of documents, signatures, records and validations involved in the process. Cross-checking data between care, administrative and regulatory systems is essential to ensure patient safety, traceability of care and legal compliance.

Among these instruments, the Hospital Admission Authorization (AIH) plays a central role. It is the document that formalizes the admission within the SUS (Unified Health System, Brazil’s public health system) and enables the processing and payment of the services provided. In this article, learn the rules, steps and critical points related to the AIH.

What is the AIH and what steps does the document go through?

The AIH is the instrument used in the SUS to authorize, record and pay for hospital admissions. It is part of the SUS Hospital Information System (SIH/SUS) and is linked to the SIGTAP table (the SUS Management System for the Table of Procedures, Medications and OPM).

The process begins with the clinical decision to admit. When the physician identifies the need for hospitalization, they fill in and sign the request report/AIH, indicating:

• the main diagnosis (ICD‑10);

• secondary diagnoses, when applicable;

• the proposed procedure;

• the clinical justification;

• the patient’s data.

From this point on, the flow involves care and administrative dimensions:

Request and report

The physician describes the clinical condition and substantiates the need for admission, taking technical responsibility for the information recorded.

Authorization

The request is sent to the authorizing body or to the municipal/state regulation department. If it meets the care and administrative criteria, the AIH number is issued.

Recording during the hospital stay

All procedures performed, complications, ICU use, tests and length of stay are linked to the AIH, forming the basis for auditing and billing.

Closing and processing

After discharge (due to improvement, transfer or death), the AIH is closed with the summary of the hospital stay. The hospital sends the data to SIH/SUS for processing and subsequent financial transfer.

A well-executed flow reduces inconsistencies, avoids processing blocks and preserves the institution’s financial sustainability.

What are the main mandatory fields of the AIH?

Filling in the AIH correctly is decisive for avoiding denials and rejections in processing. The critical fields include:

• patient identification (full name, CNS or National Health Card number, date of birth);

• establishment code (CNES, National Registry of Health Establishments);

• municipality of residence;

• nature of the admission (elective or urgent);

• main and secondary ICD‑10 codes;

• main authorized procedure (SIGTAP code);

• admission and discharge dates;

• reason for closing;

• identification and signature of the responsible physician.

Inconsistencies between the medical record and the data entered on the AIH are a frequent cause of administrative blocks. That is why cross-checking between the care team and billing is a strategic step.

Which errors most often cause denials and blocks on the AIH?

From the standpoint of hospital auditing and billing, the main problems include:

• ICD code incompatible with the procedure performed;

• procedure outside the care profile accredited in the CNES;

• discrepancy between admission dates and medical record entries;

• no justification for a prolonged stay;

• improper use of special procedures or the ICU without documented criteria.

These failures can lead to:

• technical denials;

• rejection in SIH processing;

• the need to resubmit the AIH;

• a direct impact on hospital revenue.

The quality of AIH completion is therefore not just a bureaucratic requirement but a factor that influences the revenue cycle.

Simplified AIH template (illustrative example)

Below is a simplified teaching template to aid understanding:

This template summarizes the essential fields, but the real AIH has a structure standardized by Datasus and specific processing rules.

What is the impact of the AIH on hospital management?

The AIH is a point of integration between care, regulation and billing. Issuing it correctly ensures traceability of care, supports internal and external audits, protects the institution against financial losses and builds reliable hospital production indicators.

Institutions that treat the AIH as a mere form pile up rework, inconsistencies and denials. When integrated into a data governance strategy, it becomes an operational control tool and strengthens the predictability of the revenue cycle.