How do you test for pernicious anemia? If you suspect you have PA (B12 deficiency due to a lack of intrinsic factor), you better find out fast. Once neurological damage has kicked in, you often won’t be able to revert back to your former self. For that reason, it’s crucial you hurry up and have a proper pernicious anemia diagnosis procedure.
In most countries, doctors testing for pernicious anemia don’t do a very good job at all, to say the least. Take the UK, for example, and look at the survey done by the Pernicious Anemia Society: 44% of patients were misdiagnosed with another condition; 22% had to wait for two years to get a correct diagnosis; 19% had to wait for five years; 4% had to wait for 10 years; and 14% waited for 10 years or more.
That is a catastrophe.
When you have PA and wait such a long time before starting treatment, you risk having permanent nerve damage. So, have a proper pernicious anemia test early on.
But Why Is It Misdiagnosed?
- Doctors do not test for B12 deficiency in the first place. In most countries, you actually have to ask your doctor to check your B12 status. That is absurd!
- Before testing for B12 levels, doctors often look for macrocytosis (enlarged red blood cells). But only ~60% of B12 deficient patients show them. Even neurological signs, which point to a severe deficiency, may occur in the presence of normal red blood cells. Also, supplementing with folic acid (as pregnant women do) will prevent the red blood cells from enlarging. Iron deficiency will also reduce their volume.
- In most countries, the blood level range for determining B12 deficiency is way too low. People show symptoms even at twice those levels! And the range is different depending on where you’re from. It doesn’t make sense. Why would the difference of being or not being diagnosed with B12 deficiency depend on your ZIP code?
- The blood test doesn’t give you the full picture, because it shows both active and inactive forms of B12 in the blood. Also, what happens at the cellular level is far more crucial than how much B12 is circulating in the blood. Sometimes, a patient’s levels are above the normal threshold even though he or she is symptomatic.
- The typical B12 test uses a competitive binding luminescence assay. It gives false high results in 22-35% of patients, depending on the machine. It’s not optimal:
It is important to be aware that failure of CBLA assays to detect cobalamin deficiency can occur, especially in cases of pernicious anemia where IF‐blocking antibodies have been implicated in causing assay interference.Laboratory testing for cobalamin deficiency in megaloblastic anemia.
Good Pernicious Anemia Diagnosis
How to test for pernicious anemia then? If you have been diagnosed with B12 deficiency and would like to find out if it’s full blown pernicious anemia (where your body is unable to absorb B12 unless you inject), there are some useful tests to help you.
Which Pernicious Anemia Test to Do?
Remember, the cause of PA is the body creating antibodies that make it very difficult to absorb the B12. So, how do you diagnose pernicious anemia properly? There are two types of such antibodies, and you should go test for the presence of both:
Gastric Intrinsic Factor Antibodies (IFA)
Intrinsic factor is a protein created by the parietal cells that line the stomach wall. It binds to B12 to form a complex that is necessary for the absorption of the B12 in the small intestine. 40-60% of PA patients test positive for IFAs.
The guidelines indicate that all patients suspected of having pernicious anemia should have a test for intrinsic factor antibodies, no matter what their serum B12 levels are. Even in the absence of anemia, patients with low B12 (who don’t have food-bound cobalamin malabsorption or other clear causes) should be tested.
Testing positive for IFA confirms the diagnosis of pernicious anemia. Testing negative doesn’t exclude diagnosis, because the test is not robust enough to detect all cases. If it comes back negative, you may ask to do it again several times just to make sure.
Gastric Parietal Cells Antibodies (PCA)
PCAs attack those cells that line the stomach wall. The cells normally produce both the acids that release the B12 from food, and the intrinsic factor that binds to it. Without enough IF, vitamin B12 remains largely unabsorbed, and deficiency develops.
The majority of PA patients will have PCAs. However, not everyone with PCAs will have PA. This pernicious anemia diagnostic test isn’t as specific as the IFA test, since patients with other diseases (gastritis, diabetes, and thyroiditis come to mind) may have these very same antibodies. However, if your B12 levels come in low, and you test positive for PCA, doctors will often diagnose you with PA. We advise to always test for IFA too.
Before trying to establish a pernicious anemia diagnosis, do NOT supplement with B12 for 72 hours, because it could skew your test results. Some labs may prefer not to draw a blood sample within two weeks of a B12 injection.
PCA and IFA tests should be used in conjunction with each other after other tests have established that a patient has B12 deficiency and anemia/neuropathy. However, since the treatment (B12 shots) has no side effects, the newer guidelines suggest to ignore negative test results and base diagnosis on signs and symptoms alone.
And, most importantly – to begin injecting B12 immediately.
Test Results: How to Diagnose Pernicious Anemia?
Got the results of your lab test for pernicious anemia? Here’s what to make of them:
Positive for both IFA and PCA? Immunological evidence of PA. Positive for both is the definitive test for pernicious anemia diagnosis.
Negative for both IFA and PCA? No immunological evidence of pernicious anemia.
Negative IFA but positive PCA? 90%+ to have autoimmune gastritis, which may or may not end up in pernicious anemia one day. Negative IFA does not exclude the possibility of PA, since only about half of PA patients test positive for this antibody.
Positive IFA but negative PCA? Immunological evidence of PA if the patient has low hemoglobin macrocytosis (enlarged red blood cells) and low B12 levels. If you’re older than 50, this test alone is usually enough to establish a diagnosis. A gastric biopsy may follow in order to confirm. In the absence of macrocytosis or anemia, you should repeat in six months with serum gastrin, a full blood count and fasting B12 to confirm.
Positive IFA but unknown PCA? Immunological evidence of pernicious anemia if the patient is older than 50. Test for PCA to confirm, and if negative, see above.
Negative IFA but unknown PCA? Test for PCA. Nearly half of all pernicious anemia patients test negative for IFA. In contrast, PCA is an excellent indicator of autoimmune gastritis, which often ends in pernicious anemia over the years.
Unknown IFA but positive PCA? Again, PCA is seen in more than 90% of patients with autoimmune gastritis, which may lead to PA. Of course, some people may test positive and never reach the stage of PA, so we suggest testing for IFA too.
Unknown IFA but negative PCA? Test for IFA just in case. At least 10% of those affected with pernicious anemia won’t have PCAs.
The Schilling Test For Pernicious Anemia Diagnosis
This test is no longer available. For 40 years it was used for PA diagnosis, but it involved radioactive substances that are no longer in use. Not relevant anymore.
How to Establish B12 Deficiency In The First Place?
The serum blood test for B12 is far from accurate, as it also accounts for your levels of inactive B12. The holotranscobalamin II (active B12) test, which measures only the active levels in the blood, is superior. We predict that it will replace the current tests one day, since there are often big gaps between the serum B12 and the active B12 levels. Only a few hospitals offer this test.
Methylmalonic acid (MMA) test is useful as well:
Increased MMA may suggest a B12 deficiency (MMA is high in ~95% of B12 deficient patients). However, testing positive could also mean other things, like renal disease, small bowel bacterial overgrowth, or hemoconcentration. If plasma levels are higher than 0.75 µmol/l though, it’s almost surely a B12 deficiency. It’s a great test, just not very popular, because it uses the expensive gas chromatography mass spectrometry (GC-MS).
Another useful test is plasma total homocysteine (tHcy). It’s a nice extra tool in the box, although low B6, low folate, hypothyroidism and renal failure can also elevate homocysteine levels. This test must be carried out within two hours of sampling the blood, which must be cooled during that time.
Other tests are the mean corpuscular hemoglobin (MCH) and the MCHC (mean corpuscular hemoglobin concentration), which check the amount of hemoglobin you have per red blood cell. MCHC also accounts for the volume of the cells. High levels in these tests may indicate a B12 deficiency.
All in all, you’re likely to have PA if you show low B12 or high MMA or homocysteine levels, as well as a positive pernicious anemia blood test result for IFA or PCA.
Don’t Put Off Treatment Waiting For Diagnosis
The new guidelines by the British Committee for Standards in Haematology show that the most important factor is the clinical picture. If you have clear pernicious anemia symptoms – even if your results look normal, or if you are yet to have a test – begin treatment right away. This is because B12 is a water-soluble vitamin. That means any excess goes out through your urine. No risk at all, as you can’t overdose.
If you show any symptoms, we advise to ask your doctor for a therapeutic trial of methylcobalamin B12 shots. If they refuse, or if you simply want to take control of your own health and make sure you’re getting the best form of B12, you can buy it from here. Inject daily for 3 months (your red blood cells’ life cycle), and see how you feel.
Best of luck with your pernicious anemia diagnosis, and don’t panic if you test positive. We live in an age where cheap B12 shots can keep you alive and well. Just don’t wait! With PA, waiting could mean some very real and serious nerve damage.
All the best.