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Updated - Vitamin B12 levels – Choosing when to test, wisely
Updated
Vitamin B12 levels – Choosing when to test, wisely
Practice Points
B12 and Folate will be moving to being orderable separately in Éclair e-ordering at some point in the future
B12 requests will require an appropriate clinical indication to be tested (drop-down list provided in Éclair e-ordering to select relevant clinical indication from)
B12 is not recommended for screening of asymptomatic patients
A low B12 in an asymptomatic patient is not diagnostic of deficiency
Background
In December last year, we shared a link to an article written in 2014 by Dr Michael Crooke and Dr Ken Romeril, comparing Wellington community B12 requesting patterns at Aotea Pathology, with those of an Irish study looking at a comparable population that demonstrated the benefits of using B12 in appropriate clinical context rather than for screening in asymptomatic patients. This article also raised the potential for separating B12 and Folate testing, rather than only being able to order them together.
It’s been 4 years since that original article was circulated, and the following graph shows that requesting of Vitamin B12 has climbed by 48% on average, month on month when compared to the same period 4 years ago, without a similar increase in population or an improvement in the detection rate of low values over that of 2014, which has remain the same at around 5 - 6% of all patients tested having values below the bottom of the reference interval.
Given that the initial article indicated that B12 was being over-requested in the Wellington region in 2014, this pattern has not changed, and mirrors international trends towards over-requesting of laboratory tests.
It also gives us the opportunity to increase medically necessary Vitamin B12 testing, firstly by introducing the ability to order B12 or Folate or both together AND secondly, by introducing appropriate evidence-based clinical indications for when this test should be ordered.
Why do we care about Vitamin B12?
Vitamin B12 is one of the 9 vitamins essential for human health, and is needed for normal metabolism and DNA synthesis so it is essential for normal functioning of the brain and nervous system, and for the regeneration of red blood cells. Causes of deficiency usually fall into 2 categories: Malabsorption (from a range of causes) or dietary deficiency, and the causes are not always the same as those for Folate deficiency, hence the move to separate the ordering of these 2 tests.
Deficiency is associated with macrocytosis and potentially irreversible neuropathy and neuropsychiatric changes, and patients with specific conditions e.g. those taking long term metformin, or patients with pernicious anaemia, are at greater risk of B12 deficiency.
How prevalent B12 deficiency is, in the general population, is not clear, partly due to studies often looking only at specific subgroups rather than the general population, and also because cutoff values used to categorise deficiency are not consistent across the literature. Quoted rates of deficiency in the literature range from <1% to >20%, depending on the group being studied, but figures quoted for general populations tend to be around 6% which supports the prevalence of values below the lower limit of the reference interval, seen in our region, if not necessarily the actual prevalence of deficiency. Studies do agree that the prevalence does increase with age.
The reference interval we use at Wellington SCL is 170 – 800pmol/L, however values between 110 – 170 pmol/L are deemed to be borderline so for our data we consider 110 pmol/L to be the value below which patients are more likely to be deficient.
Is serum B12 telling you what you really want to know?
Ideally, a single test would give a clear indication of whether or not a patient is B12 deficient, however there is no single ”gold standard” test to identify B12 deficiency, and none of the current markers used (Vitamin B12, Active B12, Methylmalonic Acid, and Homocysteine) are able to do this in isolation in a general population screening setting.
Factors that can influence Vitamin B12 levels include: age, pregnancy, renal disease, liver disease, drugs and polymorphisms.
What do the international guidelines say?
The significance of test results assessing Vitamin B status should always be assessed with the clinical setting.
Routine screening for Vitamin B12 deficiency is not indicated.
There are no studies to support the use of Vitamin B12 testing in patients with dizziness or fatigue and BPAC guidelines for the investigation of tiredness do not include B12 or Folate levels.
Testing is recommended in the following settings:
Haematologic: unexplained anaemia, macrocytosis
Unexplained neurological or neuropsychiatric symptoms, e.g. subacute combined degeneration of the cord, peripheral neuropathy, dementia, unexplained neurology
GI disorders, e.g. Crohn’s diseases, coeliac disease or other stomach or small intestinal disorders, previous gastric resection etc.
Medication related: metformin, prolonged use of proton pump inhibitors or H2 receptor antagonists
Pregnancy and lactation
Long term vegan and vegetarian diets
Elderly patients >75 years
Glossitis
Retesting intervals are also covered in the literature, with the Australian Medical Benefits Scheme only funding B12 testing once every 12 months, after discerning that the majority of testing was occurring in a screening capacity. The Irish study initially recommended minimum retest period of 6 months, for monitoring but has since moved to not recommending retesting B12 levels in patients who are receiving parenteral Vitamin B12 unless their full blood count parameters or neurological symptoms fail to improve. Given the move to the requirement for appropriate clinical indications for testing, we will also comment on any samples collected within 6 months of the previous B12, highlighting that this testing does not meet the recommended minimum retest interval for B12.
What happens when we launch these changes?
With the move to Éclair e-ordering for community requestors, we will be able to support the evidence-based ordering of Vitamin B12 by making B12 orderable by itself or together with Folate (Folate will also be orderable by itself), and by introducing a dropdown list of clinically appropriate settings for the use of Vitamin B12. The list given above, will be the basis of the new dropdown list. At the same time, we will also highlight those patients that have previous results within in the recommended minimum retest period of 6 months, through the electronic ordering form, to aid decision making at the time of ordering tests.
All requests that meet the criteria will be tested, and any requests that also fall within the minimum recommended retest period will have a comment added indicating that the timing of the followup test was not appropriate given our evidence-based recommendations. Following 6 months of running with the new evidence-based measures, we will stop testing samples collected within the minimum retest period, and will only issue a comment saying why the sample was not tested.
We will review the impacts of these changes after 6 months, and share this data with you in a future newsletter.
