Doctors use different machines to measure vitamin B12 levels in your blood, but these machines don’t always give the same results. Researchers tested 19 different quality checks involving nearly 1,800 measurements to see if five popular B12 testing machines agreed with each other. They found that some machines consistently gave higher or lower readings than others, which means the cutoff numbers doctors use to diagnose B12 deficiency might not work the same way for every machine. This is important because if your test shows low B12 on one machine, it might show different on another, potentially affecting your diagnosis and treatment.

The Quick Take

  • What they studied: Whether five different laboratory machines that measure vitamin B12 in blood give similar results and whether the same cutoff numbers work for all machines
  • Who participated: 19 quality control exercises with 1,791 test measurements plus 97 real blood samples, comparing five different testing machines (made by Abbott, Beckman Coulter, and Siemens) against a reference machine made by Roche
  • Key finding: Different machines gave different B12 readings—some consistently measured higher and others lower than the reference machine. Abbott machines overestimated B12 by a small but consistent amount, while Beckman machines underestimated it. The differences were large enough that doctors cannot confidently use the same B12 cutoff numbers for all machines.
  • What it means for you: If you get a B12 test, the specific machine your lab uses matters. A result that suggests deficiency on one machine might look normal on another. This suggests you should ideally get retested on the same machine if possible, and your doctor should know which machine was used when interpreting your results.

The Research Details

Researchers gathered data from 19 quality control exercises that tested how well different B12 measurement machines performed. These exercises used standardized blood samples that had been tested many times to establish known B12 levels. They also tested 97 real blood samples from patients. They compared four different testing machines (Alinity and Architect from Abbott, Access DXi from Beckman Coulter, and Atellica and ADVIA Centaur from Siemens) against a reference machine made by Roche that is officially recognized by the World Health Organization as the standard.

The researchers used two statistical methods to check if the machines agreed with each other. The first method (ordinary least squares) looked at whether the machines gave similar results across different B12 levels. The second method (Bland-Altman) checked for systematic differences between machines and how wide the range of disagreement was.

This approach is important because it tests whether the official B12 cutoff numbers recommended by health authorities in the UK would work the same way on all machines used in different labs around the world.

When different machines give different results for the same patient, it creates confusion about diagnosis. If a patient’s B12 level is borderline (close to the cutoff between normal and deficient), they might be diagnosed as deficient on one machine but normal on another. This could lead to unnecessary treatment in some cases or missed diagnosis in others. Understanding these differences helps doctors and labs know whether they need to adjust their interpretation of results based on which machine they use.

This study is reliable because it used a large number of measurements (1,791 from quality control exercises plus 97 patient samples) and compared against an officially recognized international standard. However, the study found that even with this international standard in place, machines still don’t agree perfectly. The researchers were honest about the limitations—they noted that the differences between some machines were too large to confidently say they’re interchangeable, even though some machines performed better than others.

What the Results Show

The study found that different B12 testing machines do not give identical results. Abbott’s machines (Alinity and Architect) consistently measured B12 levels higher than the reference Roche machine—meaning they tended to overestimate how much B12 was in the blood. Beckman Coulter’s Access DXi machine did the opposite, consistently measuring lower than the reference machine. Siemens machines (Atellica and ADVIA Centaur) fell somewhere in between.

When researchers looked at the Abbott Architect machine specifically, the difference was small enough (less than 9.4%) that it might be acceptable for clinical use. However, Beckman’s machine had both systematic errors (consistently off in one direction) and proportional errors (getting worse at higher or lower B12 levels), making it less reliable overall.

The researchers found similar patterns of disagreement in both the quality control exercises and the real patient blood samples, suggesting these differences are consistent and not just random variation.

Despite the fact that the World Health Organization released an international standard for B12 measurement in 2003, the machines still don’t agree well enough to use the same diagnostic cutoff numbers across all of them. This means that a B12 level of 200 pg/mL (a common cutoff for deficiency) might indicate deficiency on one machine but be considered acceptable on another.

The study found that the disagreement between machines varied depending on the B12 level being measured. Some machines had proportional errors, meaning they were more inaccurate at very high or very low B12 levels. This is important because it means a patient with borderline B12 levels might be more likely to get different results on different machines than someone with very high or very low levels. The researchers also noted that even though an international standard exists, it hasn’t solved the problem of machine disagreement, suggesting that other factors beyond standardization affect how machines measure B12.

This research adds to a growing body of evidence showing that different laboratory machines don’t always measure the same things the same way. Similar problems have been found with other blood tests. The fact that this problem persists even with an international standard suggests that the issue is complex and may involve differences in how machines are designed, calibrated, or maintained. This study is more comprehensive than many previous comparisons because it tested multiple machines and used a large number of measurements.

The study has several important limitations. First, while the researchers tested many measurements, they didn’t specify exactly how many different patients were involved, which makes it harder to know if the results apply to all types of patients. Second, the study only looked at five different testing machines, so results might not apply to other machines made by different manufacturers. Third, the researchers couldn’t confidently say whether some of the machines truly agree with each other because the range of disagreement was too wide. Finally, the study doesn’t explain why these differences exist or how to fix them, so it identifies a problem but doesn’t provide a complete solution.

The Bottom Line

If you have a B12 test showing deficiency or borderline results, consider asking your doctor which machine was used for the test. If you need follow-up testing, try to have it done on the same machine if possible. If you switch labs, be aware that your results might look different even if your actual B12 level hasn’t changed. Healthcare providers should be cautious about using the same B12 cutoff numbers across different machines and may need to adjust their interpretation based on which machine their lab uses. These recommendations have moderate confidence because the study clearly shows differences exist, but more research is needed to determine the best way to handle these differences in clinical practice.

This research matters most for people who have been diagnosed with B12 deficiency or are being tested for it, especially if they’re getting retested at a different lab. It’s also important for doctors and lab professionals who interpret B12 tests. People with symptoms of B12 deficiency (like fatigue, numbness, or memory problems) should be aware that their test results depend partly on which machine was used. This is less relevant for people with clearly normal or clearly deficient B12 levels, as the machine differences matter most in the borderline range.

If you’re being treated for B12 deficiency, you might not see changes in your test results for several weeks to months, depending on your treatment. However, the machine differences identified in this study are immediate—they exist every time a test is run. If you switch labs and get a different result, it could be due to the machine difference rather than a real change in your B12 level. You should discuss timing of retesting with your doctor, as they may recommend waiting several weeks between tests to see if treatment is working.

Want to Apply This Research?

  • Track your B12 test results along with the lab name and testing machine used (if available). Record the date, result number, and whether it was flagged as low, normal, or high. This helps you and your doctor spot real changes versus machine differences when comparing results over time.
  • When getting a B12 test, ask your lab which machine they use and request this information on your test report. If you need repeat testing, request the same lab or machine if possible. Save all your B12 test results with the lab information so you can share complete information with any new doctors.
  • If you’re being treated for B12 deficiency, establish a baseline by getting tested at the same lab using the same machine. For follow-up tests, use the same lab when possible. If you must switch labs, note the change and discuss with your doctor whether the new machine’s different readings affect your treatment plan. Track symptoms alongside test results to get a complete picture of your B12 status.

This research describes technical differences between laboratory machines used to measure B12, but should not be used to self-diagnose or self-treat B12 deficiency. B12 deficiency is a medical condition that requires professional diagnosis and treatment. If you have symptoms of B12 deficiency (fatigue, numbness, memory problems, or weakness), consult your healthcare provider. Do not change your B12 treatment based on this article. The findings suggest that doctors should be aware of machine differences when interpreting B12 results, but your doctor is best positioned to interpret your specific test results in the context of your symptoms and medical history. Always discuss your B12 test results and any concerns with your healthcare provider.