Pre-Employment and Periodic Medical Exams: What the Law Requires

Workplace medical exams tend to be treated as a hiring formality. In reality, they're where three things intersect: a health-surveillance obligation, a clinical record that stays in the company's custody, and the evidence you'll need if the origin of an illness is ever disputed.

This guide explains what supports that obligation, what types of exams exist, and above all, what makes the documentation hold up to a review.

Where the obligation comes from

There's no single standard that says "examine everyone." The obligation is built in layers, and understanding those layers is what lets you defend a company's program.

• The Ley Federal del Trabajo (LFT), Mexico's Federal Labor Law, sets out the employer's special obligations regarding medical care and the notice of workplace risks (article 504), and it makes the medical exam a worker obligation whenever the company's internal work rules provide for it (article 134, section X).
• The Reglamento Federal de Seguridad y Salud en el Trabajo (RFSST) is the primary source — and the one most often overlooked. It requires the employer to order medical exams for occupationally exposed personnel (article 7, section IX), to maintain in-house or outsourced occupational medicine preventive services (article 49), and it details risk-by-risk medical surveillance in articles 33 through 43.
• NOM-030-STPS-2009, on occupational safety and health preventive services, defines the structure under which that surveillance is carried out: who's responsible, the comprehensive diagnosis, and the program. It doesn't itself set which exams to perform.
• Risk-specific standards are what determine the concrete exams, based on each role's actual exposure: noise, chemical agents, thermal conditions, vibration, and so on.

A practical principle follows from this: the exam program isn't defined by the org chart — it's defined by exposure. Two people with the same job title at different plants can require different surveillance.

The three points in the surveillance timeline

1. Intake. Establishes health status at the time of hiring. It's the baseline, and without it, it's very hard to later argue that a condition didn't originate at work.
2. Periodic. Follows up over time with people exposed to a risk. Its value lies in comparison against the baseline, not in the isolated data point.
3. Exit. Documents health status when the employment relationship ends. It has no single legal basis that makes it mandatory in every case, but it's the practice that protects the company most: it's the most forgotten, and the one companies miss the most when a claim arrives years later.

Notices to IMSS

When a probable workplace accident or occupational illness occurs, medical care comes with a paper trail. IMSS form ST-7 is the initial medical-care notice and classification of a probable workplace accident; ST-9 is the medical-care notice and classification of a probable occupational illness.

It's worth understanding how they actually get filled out, because it isn't what people usually assume. IMSS starts the process: the attending nurse and physician fill out the front side. The company fills out the back side, in the section for supporting data used in classification, and must return it completed within the following 72 hours. IMSS's own Occupational Health physician makes the final classification.

The usual problem isn't unfamiliarity with the forms — it's having to fill out that back side with information the medical service doesn't have on hand because it lives scattered across different files, and doing it against the clock. That's where a well-kept record stops being a requirement and becomes a tool.

This 72-hour window with IMSS is separate from, and independent of, the notice that article 504, section V of the Ley Federal del Trabajo requires the company to give the Ministry of Labor, the Labor Inspector, and the Labor Tribunal — also within 72 hours. These are two separate obligations, owed to different authorities.

An exam that was performed but can't be documented is, in a review, the same as an exam that never happened.

What makes the documentation hold up

The difference between a program that holds up and one that falls apart is rarely about the clinical quality of the exam. It's about how it got recorded.

Points that tend to get overlooked

• Tracking due dates. Knowing who has an overdue periodic exam should be a query, not a reconstruction exercise with spreadsheets.
• The separation between fitness and diagnosis. Article 50 of the Reglamento Federal de Seguridad y Salud en el Trabajo is explicit: the physicians in occupational medicine preventive services report exam results to the employer “regarding workers' fitness for work,” and they do so “with full respect for the confidentiality required by medical ethics.” HR needs the fitness result and its validity period; it doesn't need the clinical detail. That boundary needs to exist in the system, not in good faith.
• Outside labs. If a third party performs the tests, their results are still part of the record, and still sensitive data under the company's responsibility.
• Continuity. When someone changes area or plant, their exposure history and prior exams need to follow them.
• Retention. Numeral 5.4 of NOM-004-SSA3-2012 requires clinical records to be kept for a minimum of five years, counted from the date of the last medical act — not from the hire date or the termination date. For exposure to certain chemical substances, the applicable retention periods are considerably longer.

A well-documented exam program does two things at once: it protects the health of the people who work there, and it protects the company when someone asks what it did about it.