Hospitals draw blood during the hiring process primarily to confirm you’re immune to infectious diseases, screen for tuberculosis, and test for drugs or nicotine. Unlike most employers, hospitals need to protect vulnerable patients from infections their own staff could carry. That makes pre-employment blood work a standard step for nearly every clinical and non-clinical hospital hire.
Checking Your Immunity to Infectious Diseases
The most hospital-specific reason for drawing blood is a test called an antibody titer. This measures whether your immune system has enough antibodies to fight off certain infections, either because you were vaccinated in the past or because you had the disease itself. Hospitals typically check your immunity to measles, mumps, rubella, chickenpox (varicella), and hepatitis B.
These aren’t arbitrary choices. Measles has a secondary attack rate of 90%, meaning nearly every unprotected person exposed to it will get sick. Chickenpox spreads easily in clinical settings, and even vaccinated workers can occasionally catch a milder version. Healthcare workers who aren’t immune can become a reservoir for ongoing transmission inside the hospital, leading to outbreaks among patients who are already medically fragile. Most measles cases in healthcare settings involve either unvaccinated staff or staff with unknown vaccination status.
If your titer shows you lack immunity, the hospital will typically require you to get vaccinated before starting work or shortly after. Federal OSHA regulations specifically require employers to offer the hepatitis B vaccine series at no cost to any employee with occupational exposure to blood or body fluids, and it must be made available within 10 working days of your start date. The CDC recommends that all non-immune healthcare personnel be vaccinated against hepatitis B, influenza, measles, mumps, rubella, pertussis, and varicella.
Screening for Tuberculosis
Hospitals also use blood draws to screen for tuberculosis. The blood-based TB test, known as an interferon-gamma release assay, is increasingly replacing the older skin test (the one where a nurse injects a small bump under your forearm and you return two days later to have it read). The blood test has roughly the same sensitivity as the skin test but is more specific, meaning fewer false positives. That’s especially useful for people who received the BCG vaccine as children, which is common outside the United States and can trigger a misleading positive on the skin test.
From the hospital’s perspective, the blood test is also simpler logistically. It requires only one visit instead of two, doesn’t need a trained reader to interpret the result, and eliminates the need for baseline two-step testing during annual screening. For a large employer onboarding dozens of new hires at a time, that efficiency matters. A positive result doesn’t necessarily mean you have active TB. It means you’ve been exposed and need further evaluation, usually a chest X-ray, before you can start working around patients.
Drug and Substance Testing
Pre-employment drug screening is standard at virtually every hospital, though it’s often done through urine rather than blood. The federal baseline panel covers five drug categories: amphetamines (including methamphetamine and MDMA), cocaine, marijuana, opiates and opioids (including heroin, codeine, hydrocodone, oxycodone, and morphine), and PCP. Many hospitals use an expanded 10-panel test that adds benzodiazepines, barbiturates, methadone, and other substances.
Hospitals are particularly strict about drug screening because their employees handle controlled substances, operate medical equipment, and make decisions that directly affect patient safety. Passing the drug test is a condition of the job offer, and a positive result almost always means the offer is rescinded. On a case-by-case basis, specimens can also be tested for any Schedule I or II controlled substance.
Nicotine and Tobacco Screening
Some hospitals go a step further and test for nicotine or its metabolite, cotinine, as a condition of employment. This is more common at cancer centers and health systems that have adopted tobacco-free hiring policies. MD Anderson Cancer Center, for example, screened over 41,000 applicants for tobacco use between 2015 and 2024. Fewer than 1% tested positive, suggesting the policy largely deters tobacco users from applying in the first place.
Whether a hospital can legally refuse to hire you for nicotine use depends on where you live. Twenty-nine states have smoker-protection laws that treat tobacco users as a protected class during hiring. In the remaining states, hospitals are free to enforce nicotine-free policies. This screening is typically done through urine rather than blood, but it’s often bundled into the same pre-employment testing appointment.
What Happens If You Lack Immunity
A common concern is what happens if your blood work reveals a gap. For most diseases, the solution is straightforward: you get vaccinated. Hospitals generally cover the cost of required vaccinations, and OSHA mandates that hepatitis B vaccination be provided free of charge to at-risk employees. You can even initially decline the hepatitis B vaccine and accept it later while still employed, though you’ll need to sign a declination form.
For TB, a positive blood test triggers additional evaluation but doesn’t automatically disqualify you. Many healthcare workers test positive for latent TB exposure and work safely with appropriate monitoring or treatment. The goal of the screening isn’t to eliminate every worker with a past exposure. It’s to identify active infections before they can spread in the hospital.
Why Blood Specifically
You might wonder why hospitals can’t just ask for your vaccination records instead of drawing blood. The short answer is that records are often incomplete or unavailable. Many adults don’t have documentation of childhood vaccines, and even those who do may not have received every dose in a series. A titer gives objective proof of immunity regardless of your paperwork. It’s also possible to have been vaccinated and still not developed adequate immunity, which a titer will catch but a vaccination record won’t.
Blood draws also allow hospitals to run multiple tests from a single sample. One tube can be used to check immunity to several diseases at once, screen for TB, and run any additional tests the occupational health department requires. For the hospital, this consolidates what would otherwise be weeks of back-and-forth into a single appointment, getting you cleared and on the floor faster.