MBS Update: HbA1c for Diagnosis of Diabetes

Well there’s nothing like a bit of gentle peer pressure to generate some new FOAM content! Victorian GP, Dr David Corbet, recently tweeted about the new changes to HbA1c testing in the MBS criteria. A brief Twitter conversation followed and as a result, David has not only produced a handy summary about the use of HbA1c, but has also created a new Tumblr which promises to be a great new source of GP gems.

Here’s a link to David’s Tumblr and the original post.

And here it is reproduced with permission:

From November 1 2014 there have been a number of changes to rebates for pathology tests that will have a significant impact on General Practitioners. The main one being the use of the HbA1c for diagnosis of Diabetes Mellitus.

For those of you short on time, here’s the low down:
you can now order a single HbA1c test every 12 months for asymptomatic high risk patients to diagnose diabetes. A result equal to or above 48 mmol/mol (or 6.5% in the old usage) is diagnostic, although lower readings don’t necessarily exclude diabetes.

Hooray! You can download the official documentation from Medicare here.

For those of you with nothing better to do, read on for a little more info and feel free to add comments, ask questions or get involved.

Many countries already use HbA1c, a measure of long term blood glucose control, for diagnosis of diabetes with threshold criteria adequately described in the literature. In Australia we use a fasting glucose of ≥ 7mmol/L (measured on two separate occasions) for diagnosis, or more commonly, having found a raised but non-diagnostic fasting glucose, a postprandial glucose ≥ 11.0 mmol/L from a Glucose Tolerance Test (GTT) (also meant to be on two separate occasions). The GTT is a time and resource consuming test, where a glucose load is given to a fasting patient and their blood glucose levels measured 3 times over a two hour period. Lots of patients have complained to me about the glucose load, primarily due to the intense sweetness and the occasional nauseous vomit.

Up until November 1 this year you could order an HbA1c to monitor control of blood glucose in a patient with known diabetes and receive the medicare rebate 4 times a year. This hasn’t changed, but now there is a rebate available to diagnose “high risk” asymptomatic patients:

Quantitation of HbA1c (glycated haemoglobin) performed for the diagnosis of diabetes in asymptomatic patients at high risk. (Item is subject to rule 25)

Rule 25 appears to relate to the frequency of testing – in this case only once every 12 months to get a rebate. A quick search on the medicare website failed to provide a list of the rules, but I’m curious to read them if anyone has access.

So, what criteria determines if a patient is high risk?

I think it’s safe to say that we can rely on the AUSDRISK guidelines / evaluation to determine high risk patients, defined as a score of 12 or more. Then again, given the machinations of medicare, it’s probably best not to assume anything!

The RACGP 2014-2015 guidelines do support the use of HbA1c ≥ 48 mmol/mol for diagnosis but state readings needed on two separate occasions. It will be interesting to see how they adjust their flow chart for diagnosis to accommodate that only one HbA1c test would get the rebate under the current system!

Other considerations

Limitations of the HbA1C:
Given the assay evaluates glycated haemoglobin from red blood cells, anything that reduces the survival time of red cells will change the result. This becomes important when considering co-morbidities, such as chronic renal failure, post-splenectomy, anaemia and haemoglobinopathies – although the effect of haemoglobinopathies also depends on the type and it’s recommended you talk to your local friendly path lab first if ordering the test. In patients who have had a blood transfusion or therapeutic venesection it is necessary to wait for 3 months to do the test.

The GTT costing from the MBS website shows
Fee: $18.95 Benefit: 75% = $14.25 85% = $16.15
and for the HbA1c
Fee: $16.80 Benefit: 75% = $12.60 85% = $14.30

What’s not to like! Lower cost, equivalent diagnostic test, less resource dependent, more tolerable test, meets international standards. Well done medicare.

The next post will cover some of the other changes. Including strict criteria for Vitamin D testing.


7 thoughts on “MBS Update: HbA1c for Diagnosis of Diabetes

  1. It’s a funny thing diabetes… The diagnosis is arbitrary. Random (or 2 h post-OGTT) BSL of 11.1 mmol/L is 200 mg/dL. Why 200? Why not 199 or 201? This simply reflects human preference for round digits and consequences of historical decisions.

    The HbA1c diagnosis does pose a bit of a philosophical problem as it doesn’t map that well to the OGTT/fasting BSL diagnosis. Where do the fuzzy edges lie – and what does it mean? For instance, I have diabetes using the classic criteria, but I wouldn’t using HbA1c (mine is 6.3%).

    In all of this, the concept of “pre-diabetes” is gaining traction. This is an even more problematic construct – most people with “pre-diabetes” don’t seem to actually progress to diabetes after 10 years.

    Interesting times!

    • HbA1c is potentially misleading as a diagnostic test, and to rely on it would be to accept a considerable lag time between onset of clinically significant hyperglycaemia and diagnosis/treatment. With increasing evidence that T2DM (in particular) is best addressed early to promote the legacy effect, it may be a test more appropriate for patients in remote areas not able to access pathology services for fasting blood tests, or patients who clinicians are concerned may not follow up. The issue is more than the consideration of IFG and IGT, as they form the first part of the spectrum of dysglycaemia, but it is the concern of patient inaction with a ‘high-normal’ test result and the impending progressive dysglycaemia being left unaddressed.

      • If the HbA1c is less than 6.5, then the hyperglycemia isn’t significant and so no diabetes management is required.

        A patient may have a slightly raised fasting sugar and go on to an OGTT which give a biochemical diagnosis of IGT or diabetes, but again, they don’t have clinically significant diabetes unless HbA1c is more than 6.5. So if fasting glucose or OGTT is raised in someone with a normal HbA1c then…it can be ignored for a year.

        Presumably they had the fasting glucose or OGTT done because of a high AUSDRISK in the first place, so just repeat the HbA1c in a year which is within the medicare schedule- just as you would repeat an OGTT in a patient with IGT in a year.

        See Australian prescriber, volume 37, number 3. June 2014.

    • Re Kate Johnson
      HbA1c test should NEVER be done in Isolation Why?
      our C.A.L.D population which has the highest T2D,most Hospitalisations in Australia,and Highest Morbidity
      rates, are susceptable to Variant Haemoglobins (over !000 variants) or Haemoglobinopathies identified here,as S.MAmericaned(Greek;Italian;spanish etc)Middle Eastern(highest with variants);Chinese;SE Asian;Blacks,African and American;Indian Sub Continent including Sri Lanka;Latin Americans;NZ Mauris;
      Pacific Islanders,And Some W A and NT aboriginal communities
      these conditions give falsley low or high A1cs see 8.1 RACGP guidelines 2014-15
      Other more common conditions related more to women,ie heavy Menstruation;IDA,Vitb12Def,folate
      acid def. etc can give falsley high A1c so in DM if not spotted women are can be overmedicated causing
      In my case over a 20yr period with A1cs Ranging from 3.8 to highest 5.5 I was not medicated though
      FBG readings wereALL out of control— 15.5 this was assumed “good control”: by Many GPs.
      it has since been found that both GPs and Path Labs did not “Sight “Discordant results–finally diag.
      with low grade hemolytic anemia (see Prof L Burnett Dr B campbells’ MJA article
      So there are LIMITATIONS to HbA1c both in Diagnosis AND Diabetes Management.
      finally on “conmments on PIPs,there is a RACGP Std attached (but not implemented) that states
      GPs should update their Knowledge!!! have you read sect 8.1 2014-15 RACGP guidelines??
      Simple math rule 2xA1cv-6=Av BGM readings

  2. Potential downside. The Pip payments made re percentage of patients having had a cycle of care for diabetes is measures based on the number of patients who have had a HbA1c performed not the number who actually have diabetes. Thus the ability to generate more numbers of potential diabetes automatically reduces the percentage who have had cycle of care sent as an item number. Recognising whether or not someone has had a cycle claimed is a potentially irrelevant measure of care, it is potential part of profit. Yet another area of govt payments decreasing without compensating mbs increases for consultative medicine.

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