Companion diagnostics: when a medicine needs a test first

Creator: Reserve Meds
Published: 2026-10-17

A plain explanation for patients, families and doctors, checked against the regulator's own pages on 17 October 2026.

Reviewed by the Reserve Meds clinical operations team on 17 October 2026. Sources accessed 17 October 2026.

The short answer

A companion diagnostic is a test, usually a laboratory test, that provides information essential for the safe and effective use of a specific medicine. It identifies who is likely to benefit or who is at higher risk. When a US label requires a test result, the treating team needs that result before a hospital can justify an import request.

Who regulates the tests: US FDA (medical devices).
Where to check: FDA's list of authorized companion diagnostic devices.
Why it matters: The label's patient group is defined by the test result.
Before requesting: Have the test result in the file.

What a companion diagnostic is

FDA defines a companion diagnostic as a medical device, often an in vitro diagnostic, that provides information essential for the safe and effective use of a corresponding drug or biological product. It can identify patients most likely to benefit, identify patients at increased risk of serious side effects, or monitor response so treatment can be adjusted. If the test is inaccurate, the treatment decision may not be optimal.^[1]

FDA keeps a public list of authorized companion diagnostic devices, both in vitro and imaging tools. FDA issued final guidance on in vitro companion diagnostics on 6 August 2014, and in April 2020 final guidance allowing class labeling for tests used with groups of oncology therapies.^{[2, 1]}

Examples from medicines we cover

Current US labels for several targeted medicines define the patient group by a test result. The label for Revuforj covers acute leukemia with a KMT2A translocation as determined by an FDA-authorized test. Emrelis covers non-squamous non-small cell lung cancer with high c-Met protein overexpression. Komzifti covers relapsed or refractory AML with a susceptible NPM1 mutation, and Modeyso covers diffuse midline glioma with an H3 K27M mutation.^{[3, 4, 5, 6]}

What this means when requesting a medicine from abroad

Ask the treating oncologist or specialist which biomarker the US label requires, and whether the test has been done.
Ask whether the hospital's laboratory can run it, or whether a sample needs to be sent to a reference laboratory.
Keep the full laboratory report in the file. A regulator or hospital committee reviewing an import request will want to see that the patient matches the label.
If the result does not match the label's group, the medicine is being considered off-label, which many named-patient routes do not support. Discuss this openly with the specialist.

Until a medicine is registered locally, a patient in the Gulf usually reaches an FDA-approved medicine through a hospital request to the national regulator, such as the SFDA Special Access Program in Saudi Arabia or the procedure in NHRA Circular 41 of 2020 in Bahrain.^{[7, 8]}

Accelerated approval and biomarker-defined indications

Several biomarker-defined cancer indications are approved under accelerated approval, based on response rate and duration of response, with continued approval tied to confirmatory trials. The Bizengri label, for example, covers cancers with an NRG1 gene fusion under accelerated approval.^{[9, 10]}

Questions to ask the treating specialist

Which biomarker does the US label require, and which test method is acceptable?
Can our laboratory run it, and how long will the result take?
If the result is borderline or negative, what are the alternatives?
Will the hospital include the test report in its request to the regulator?

How Reserve Meds helps

Reserve Meds is a digital health company. Medicines are supplied through a US-licensed pharmaceutical wholesale partner. We help families and treating doctors understand the route, prepare the documents the regulator or hospital asks for, arrange supply from the US once approval is in place, and keep everyone updated. We do not diagnose, prescribe or decide what a regulator approves.

We coordinate access to FDA-approved medicines only. Investigational medicines are only available through a manufacturer's expanded-access program requested by the treating physician; we can explain that route, but we do not supply them. Your coordination fee is quoted in writing for your case before you commit. No hidden charges. We give you a written timeline estimate for your case before you commit.

Ask us whether a medicine can reach your patient

Tell us the medicine, your country and a WhatsApp or phone number. We reply within one business day. On WhatsApp we usually reply the same day.

Frequently asked questions

What is a companion diagnostic?

A test, usually an in vitro diagnostic, that gives information essential for the safe and effective use of a specific medicine, such as whether the patient's tumor has the targeted mutation.

Where can I check whether a test is FDA-authorized?

FDA publishes a list of authorized companion diagnostic devices, covering in vitro and imaging tools.

Do I need the test result before asking for a targeted medicine?

In practice yes. The US label defines who the medicine is for by the test result, and an import request will be judged against that.

Can Reserve Meds arrange the test?

No. Testing is arranged by the treating team and laboratory. We help with the medicine once the treating doctor and regulator have what they need.

Sources for these answers: ^{[1, 2]}

Sources

All sources were opened and checked on 17 October 2026. Rules and labels change, so the treating hospital or regulator confirms the current position before anything is filed.

US FDA: Companion Diagnostics (accessed 17 October 2026)
US FDA: List of FDA-Authorized Companion Diagnostic Devices (In Vitro and Imaging Tools) (accessed 17 October 2026)
DailyMed: Revuforj (revumenib) US prescribing information, version effective 4 February 2026 (accessed 17 October 2026)
DailyMed: Emrelis (telisotuzumab vedotin) US prescribing information, version effective 25 May 2025 (accessed 17 October 2026)
DailyMed: Komzifti (ziftomenib) US prescribing information, version effective 9 December 2025 (accessed 17 October 2026)
DailyMed: Modeyso (dordaviprone) US prescribing information, version effective 9 January 2026 (accessed 17 October 2026)
SFDA: Special Access Program (SAP) guidance, version 1.0 (accessed 17 October 2026)
NHRA Bahrain: Circular No. (41) of 2020, procedures for importing non-registered medicines (accessed 17 October 2026)
US FDA: Accelerated Approval Program (accessed 17 October 2026)
DailyMed: Bizengri (zenocutuzumab) US prescribing information, version effective 19 May 2026 (accessed 17 October 2026)

This page is general information, not medical or legal advice. It does not replace advice from your own doctor or the regulator.