Internal Audit and External Audit: Two Lenses on the Same Warehouse

Two audit teams can inspect the same inventory without answering the same question. Clear objectives explain where their work overlaps, where it differs and whether one team can use work performed by the other.

Consider an original fictional food distributor. Its warehouse receives packaged goods, tracks expiry dates and routes stock exceptions to responsible managers. Internal audit has reviewed how expiry alerts are investigated. The external financial-statement audit team is planning its inventory work. A report is available, but that fact alone does not make it suitable evidence for a different engagement.

Start with the purpose of each engagement

Internal audit can examine governance, risk management and controls across the organization, within its mandate. In this case, the question might be whether expiry alerts reach the right person and lead to an evidenced decision before stock becomes unusable. Work could follow the alert from the system to the warehouse review, management action and subsequent monitoring.

The external financial-statement audit has a different overall purpose: an opinion on the financial statements under the applicable framework. Here, inventory questions could concern whether recorded stock exists, whether its condition affects valuation, and whether relevant movements are recorded in the correct period. This is one type of external audit; external assurance services are not limited to financial statements.

The distinction is not operations versus numbers. Internal audit may examine financial reporting controls, and a financial-statement auditor may need a detailed understanding of warehouse operations. The engagement objective determines what the evidence must support.

Ask what the existing work actually covers

Suppose internal audit inspected the escalation process during a midyear review. Its work documents whether selected expiry alerts were assigned and investigated. That could help another team understand the process and identify questions to pursue.

It would not, by itself, establish the condition of year-end stock or the appropriateness of a year-end valuation estimate. The reporting date, population, procedures and purpose differ. A later system change or a different warehouse may also affect relevance. A useful report can be relevant to understanding risk while remaining insufficient for a particular audit conclusion.

Potential use requires evaluation

ISA 610 requires the external auditor to assess whether internal audit work can be used, including the function's objectivity, competence and disciplined quality processes. Relevant work must also be evaluated for adequacy; the external auditor's procedures include reperforming some of it. Greater judgment and risk can require more work by the external auditor directly. The external auditor retains responsibility for the audit opinion.

For this fictional warehouse, a practical discussion would compare the alert population, period, test evidence, review trail and remaining gaps. One possible outcome is that part of the work is usable. Another is that it informs risk assessment while the external team performs separate procedures. Neither outcome should be assumed merely because a report says satisfactory.

Preserve the differences in independence and responsibility

Internal audit needs an organizational position that supports objective work and access to the board. That is distinct from the independence required of an external financial-statement auditor. An internal audit function can also be outsourced; the label internal describes its role, not necessarily an employment contract.

The IIA's Standard 9.5 supports coordination with other assurance providers. Where internal audit relies on another provider, its own conclusions remain its responsibility. Coordination is useful; responsibility does not move with a shared working paper.

Using work already performed by the internal audit function also differs from asking internal auditors to perform procedures under the external auditor's direction. ISA 610 addresses direct assistance separately, and laws or regulations may prohibit or restrict it. This article does not assume permission in any particular jurisdiction.

A small exercise for a clearer assurance conversation

Choose one warehouse risk and write each team's question separately. Identify the period, population and evidence each question needs. Then mark the overlap and the gaps. The exercise should produce a better discussion of scope, rather than a blanket promise of reduced testing.

This is an original educational case, not a finding about a real distributor or a complete reliance assessment. Consult the applicable standards and local requirements for an actual engagement. References are ISA 610 in the IAASB 2026 Handbook and The IIA's 2024 Global Internal Audit Standards, including Domain I and Standard 9.5.

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