This month’s blog post is about the Schilling Test. The Pernicious Anaemia Society frequently gets questions about this from our members and many hark back to ‘the good old days of the Schilling test’ in terms of their diagnosis. Ebba Nexø is an esteemed expert in the field of B12 with many publications in her name and is Professor emerita at Aarhus University Hospital, Department of Clinical Medicine where she is involved in research in various aspects of mainly biomarkers for B12 status. She is an active member of CluB-12, a group of international researchers and medics, and is a highly respected contributor to their discussions and to improving the improved education of scientists and medical professionals on the subject of Vitamin B12. In this blog post Ebba looks the history of the Schilling Test, why it is no longer used and what the current – also less than perfect – alternatives are.
The Schilling’s test and other options
Introduction
Once the diagnosis of B12 deficiency has been established the next question is to understand why the patient suffers from this condition. This is important to know, prior to suggesting an efficient long-term treatment or prevention strategy.
If B12 deficiency is caused by a lack of B12 in the diet a change in diet is requested, or alternatively, a daily vitamin pill should be administered together with a meal. But if the deficiency is caused by an irreversible inability to absorb the vitamin, a lifelong treatment with pharmacological doses of B12 is needed. Pernicious anemia (PA) represents such a condition. The patient lacks intrinsic factor, a protein mandatory for the intestinal uptake of a physiological dose of B12. In PA patients the parietal cells that produce intrinsic factor is destroyed due to an autoimmune reaction that also leads to an atrophic gastritis.
It may sound simple to decide the right treatment strategy, but the big question is how to identify patients able to absorb vitamin B12 provided by food or a vitamin pill, as compared to those who have lost the capacity to absorb vitamin B12.
In the old days the Schilling’s test helped to solve this question.
The no longer available Schilling’s test
Back in the 1950s Robert Friederick Schilling (born in 1919) introduced the test that bears his name: the Schilling’s test. The concept is simple. Give the patient a drink with a radioactively labeled B12. If all the radioactivity is excreted with feces the patient is not able to absorb the vitamin, but if it enters the body the capacity for uptake of B12 remains.
Various versions of the test have used different methods to measure the amount of B12 absorbed. The most common method, also introduced by Schilling, is to inject a high dose of unlabeled B12 to saturate all binding capacities of the B12 binding proteins, and thereby facilitating urinary excretion of the absorbed radioactively labeled B12. Thus, the radioactivity excreted in the urine during the 24 hours following the administration of the labeled B12 will reveal the answer. If the excretion of radioactive B12 is below a set limit the patient is unable to absorb B12, but if a high amount of radioactivity is excreted the patient can absorb the vitamin. Other methods for detection of the absorbed amount of an administered dose of radioactive B12 have been employed, such as estimating the amount of radioactivity excreted with feces. If all radioactivity is excreted, the patient is unable to absorb B12, while a low fecal excretion of the radioactive B12 indicates that some of the vitamin has been absorbed.
The Schilling’s test was further developed to include the Schillings Test II. This test aimed to demonstrate whether a lack of uptake of B12 could be normalized by adding intrinsic factor to the radioactive B12. If B12 uptake was increased by addition of intrinsic factor, it supported that this was exactly the protein the patient was lacking, such as is the case in PA. If the uptake did not increase after addition of intrinsic factor the B12 malabsorption was likely to be caused by an intestinal condition.
The Schillings test was by no means perfect. Using measurement of radioactivity excreted in the urine, a test result indicating uptake of B12 was considered conclusive, whereas a test result suggesting no uptake should be judged with caution. Did the patient swallow all the radioactive B12? Was the injection of unlabeled B12 done at the right time? Was all the 24-hour urine collected? And perhaps most important, was the test done at a time where the gastrointestinal tract still suffered from lack of B12, and because of that had a temporary decreased capacity for uptake of B12?
Despite the limitations, the Schilling’s tests were widely used until the mid-nineties. After that it slowly disappeared because it became more and more difficult to obtain radioactive B12 suitable for human use, and at the same time less and less acceptable to use radioactive B12 in a diagnostic test. In addition, facilities for detecting the radioactive B12 in a 24-hour collection of urine slowly vanished as did sources for intrinsic factor that could be used in humans. Originally the source for intrinsic factor was virtually unprocessed normal gastric juice obtained from healthy volunteers.
Today, it is unfortunately no longer possible to perform the Schilling’s tests.
How to judge the absorption of B12 without the Schilling’s test
A few attempts have been made to use the concept of the Schilling’s test employing non-radioactive forms of B12. One very elegant design is to use a form of B12 that can be detected by rather sophisticated methodologies in a blood sample. The test involves intake of a test dose followed by removal of a blood sample for measurement of the administered form of B12. While this principle has shown great promise in the research setting it has not yet come into routine use.
Another concept is to measure B12 bound to the plasma protein transcobalamin (holoTC, active B12) before and after administration of three high physiological doses of B12 for two days. A lack of increase in holoTC supports an impaired capacity for uptake of the vitamin. The test is named CobaSorb and is in routine use in Denmark but is yet to be more widely employed. A CobaSorb test showing a clear increase in holoTC supports a normal uptake, while an increase below a set limit should be taken with some reservation before a conclusion of a permanent impaired uptake of B12 is made. A major issue is that the test must be done prior to treatment with pharmacological doses of the vitamin, and thus the patient may display a temporary B12 malabsorption caused by an intestine suffering from the lack of B12.
So far, internationally we have no test that can replace the Schilling’s Test II, examining the uptake of B12 when it is supplied together with intrinsic factor. Attempts have been made to produce recombinant human intrinsic factor suitable for human use, but so far it is not recognized for use in the clinic.
Other means are available for diagnosing the presence of B12 malabsorption caused by PA, the autoimmune disease that destroys the cells producing intrinsic factor. Detecting atrophic gastritis upon gastroscopy strongly supports the diagnosis, as does a positive finding of autoantibodies against intrinsic factor in a blood sample. However, a negative result for those antibodies is of limited value, since some patients with PA lack the antibodies. Detection of autoantibodies against the parietal cells producing intrinsic factor is of less value, since a positive result may be present also in patients not suffering from PA and some patients with PA will show a negative result.
Conclusion
Though not perfect, the no longer available Schilling’s test presented a useful option for judging the uptake of B12 and for clarifying whether an impaired uptake was caused by the lack of intrinsic factor.
Other tests may help to diagnose PA, such as the presence of an atrophic gastritis and autoantibodies towards notably intrinsic factor, but we lack routine procedures that can fully replace the Schilling’s Tests. Current attempts such as the CobaSorb Test and tests employing a detectable non-radioactive form of B12 may prove to be reasonable alternatives for the original Schilling’s Test, and thereby help to solve the most important question: Will this patient need a lifelong treatment with pharmacological doses of B12?
Reintroduction of the Schillings test II, exploring whether a diagnosed B12 malabsorption is caused by lack of intrinsic factor, would require the availability of intrinsic factor suitable for use in humans.
Ebba Nexø
Having had two Schilling tests done (one in 1968 the other in 1972) I was intrigued to read what it was all about – Thank you.
The first test was inconclusive the second showed that I had P,A – this 13 years after a gastrectomy following a perforated peptic ulcer at the age of 17 in 1959.
My then doctor gave me two or three years to live without treatment and put me on cyanocobalamin every four weeks – I’m now coming up to 83 – so I guess they are working
Thanks again for an interesting article
Clive Parsons
Thank you for being there..
Im sure many of us are looking forward to some new tests that are more modern and accurate for PA. Thanks for this blog.
My husband was diagnosed with PA about 20 years ago. He is currently have neurological symptoms despite his weekly/monthly IM shots of B12. Are there any cases of the body not absorbing the shots? Any help would be grateful!!
My husband is the same. He takes B12 injections monthly, but his neurological symptoms (numbness in legs and arms, timgling, itching, etc) have never improved. Thank you for asking this question. I’d love to hear a good answer…..if there is one.
I started to recover when having 3 x B12 injections per week, but the recovery stalled when reduced to once per week and I started again to decline when I was having just one injection per 2 weeks. I now take sublingual B12 (Superior Source, Microlingual), at least 3 times per week in addition to 4 weekly injections. I have Exocrine Pancreatic Insufficiency (EPI) and take Creon; had an overdose of Nitrous Oxide in childbirth, apparently destroying my ability to store (enough?) B12 in the liver; until recently had gastritis and was taking daily PPI. B12 deficiency problems started after the Nitrous Oxide overdose aged 25, (am now 80). The reasons for deficiency can be cumulative, there isn’t a one size fits all as far as B12 dosage is concerned.
I had a B12 crash from probably a lifetime (vegetarian) of insufficient B12. Officially diagnosed 2015, crashed 2022. I was never followed up correctly and I just didn’t realise it had been overlooked in my appointments. Anyone with PA should probably be taking injections daily for the rest of their life. I have never taken PPIs but do know that they deplete B12. Metformin is another medication that depletes B12. I did 1 year of daily injections and the next year did EOD (every other day) injections. Very recently I thought surely I was able to go onto having an injection only when I felt I needed it,boy was I wrong. All hell broke lose, so now I am back to everyday again. Hard lesson. I don’t know how far it has set me back, but it has. I was doing really well.
Some people apparently need B12 every day or every other day, (Martyn Hooper mentions this in his book), I have read various suggestions as to the reason. I have a monthly injection plus I take a daily Methylcobalamin (B12) sublingual (under the tongue), tablet, (sometimes 2) – Superior Source brand. This regime at least prevents me from getting any worse. The brand I take doesn’t contain fillers, absorbs in 15-20 seconds, no taste.