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You Make the Call: Would you conduct variant hemoglobin testing in a pediatric patient with iron deficiency?

July 31, 2023

August 2023

Ellis J. Neufeld, MD, PhD, Executive Vice President, Clinical Director, St. Jude Children’s Research HospitalEllis J. Neufeld, MD, PhD
Executive Vice President
Clinical Director
St. Jude Children’s Research Hospital

 

 


CLINICAL DILEMMA

In the pediatric setting, is it worthwhile to conduct variant hemoglobin (Hb) testing in a patient who has been diagnosed with or is in treatment for iron deficiency? I am concerned about this from a Choosing Wisely perspective, as many such test orders in our system are in the setting of known iron deficiency or where it is highly likely based on red cell indices and blood counts. Discussion around this topic has been sensitive, given that these patients are children, not adults. Among the argument against testing is a call for the minimization of needle sticks, though this does not address the question of whether the testing should be done at all.


EXPERT OPINION

This question is indeed amenable to a “Choosing Wisely” mindset to control unnecessary or misleading testing. Several principles and diagnostic considerations should be kept in mind:

  1. Hemoglobin (Hb) electrophoresis is the screening test of choice to assess for elevated HbA2 in beta thalassemia trait and other variants, but it can’t detect alpha thalassemia trait. Importantly, iron deficiency can falsely lower HbA2, so if beta thalassemia trait is suspected, iron repletion should precede testing.  
  2. Alpha globin gene analysis by molecular methods is not iron dependent. If there were a pressing need to understand alpha globin deletion states, as for cases of HbH alpha thalassemia or for prenatal counseling, this testing could be ordered at the outset. An example might be a pregnant mother of South Chinese or Southeast Asian descent who has microcytosis and whose partner also has microcytosis or unknown alpha thalassemia status.
  3. A circumstance familiar to hematologists, pediatricians, and general practitioners is the case of a teenage woman with iron deficiency that is already proven or is suspected based on dietary and menstrual history who is from a population with prevalent thalassemia trait, such as African, Middle Eastern, or South and Southeast Asian heritage. Such a patient could have both thalassemia trait and iron deficiency; this is very common as, conservatively, more than a billion humans, particularly women of child-bearing age, have iron deficiency, and more than 200 to 300 million people have thalassemia trait, so the overlap is substantial.
  4. In addition to iron studies, other readily obtained parameters may suggest an answer without having first to be fully iron replete. The Mentzer index, calculated as mean corpuscular volume (MCV) divided by the number of red blood cells (RBCs),1 is very low (<13) in thalassemia trait, in which cells are both small and numerous, whereas in severe iron deficiency, hematopoiesis is suppressed, so the number of RBCs is also suppressed and the index is higher. Unfortunately, this index is often indeterminate (14-17), and a frequent cause of non-diagnostic index is concurrent iron deficiency and thalassemia trait. 
  5. The CHr (known as reticulocyte Hb content or its equivalent, available with slightly different names and normals in various analyzers) is helpful because it is low in both thalassemia trait and iron deficiency, needs no special Hb identification, and corrects only with treated iron deficiency. Further, it corrects more quickly than bulk Hb or MCV — within a few days of starting iron, rather than a few weeks.2  

To summarize, in the context of your question: whenever possible, if iron deficiency is suspected by history or known from lab studies (low ferritin with low transferrin saturation), there is a “Choosing Wisely” rationale for deferring Hb identification. In a person who could have both alpha thalassemia trait and iron deficiency with an indeterminate Mentzer index, a trial of iron with retesting of the CHr in a week may be helpful. Alpha globin gene analysis can be done any time if necessary but can be deferred if not urgent. If beta thalassemia trait is suspected based on ethnicity (or in an adopted patient of unknown ethnicity) and one must make a diagnosis, Hb electrophoresis should wait for iron repletion. Of course, if iron repletion entirely corrects the Hb, CHr, and eventually the MCV, then the patient most likely didn’t have thalassemia trait and needs no further testing.  

As the question supposes, it is regrettable that all these tests are sent concurrently “to save on blood draws.” The wiser approach is to understand the tests and make a rational plan.

References

  1. Mentzer WC Jr. Differentiation of iron deficiency from thalassaemia trait. Lancet. 1973;301(7808):882.
  2. Brugnara C. Reticulocyte cellular indices: a new approach in the diagnosis of anemias and monitoring of erythropoietic function. Crit Rev Clin Lab Sci. 2000;37(2):93-130.

NEXT MONTH'S CLINICAL DILEMMA

 

I have a 38-year-old male patient with newly diagnosed hairy cell leukemia. Prior to diagnosis, he experienced intermittent night sweats for several months but had no other symptoms. His primary care physician detected an abdominal mass on physical exam. His blood counts at the time were the following:

  • White blood cell (WBC) count: 40.8 x 10⁹/L
  • Absolute lymphocyte count (ALC): 38.8 x 10⁹/L
  • Absolute neutrophil count (ANC): 0.8 x 10⁹/L
  • Hemoglobin (Hb): 9.2 g/dL
  • Mean corpuscular volume (MCV): 89 fL
  • Platelets: 50 x 10⁹/L

An abdominal and pelvic CT scan revealed 32.2 cm spleen, with nodular mass effect on adjacent organs. On review of the slides from a biopsy of the mass, hairy cells were identified. On peripheral blood flow cytometry, an abnormal population of cells consistent with hairy cell leukemia expressing CD5, CD11c, and CD103 (93% of the events) was found. The bone marrow was hypercellular, and 80-90% replaced with monoclonal atypical B-cell proliferation expressing the same markers as seen in peripheral blood. He had 2.03% mutated immunoglobulin heavy chain (IGHV) gene, which is considered borderline positive, and BRAFV600E mutation was present.

I told the patient that cladribine was the standard of care. However, there has been some investigation of adding rituximab, which seems to produce deeper remissions that could translate to longer first remission, but there is no evidence of cure. This may be at the expense of additional immunosuppression and the risk of infusion reactions, among other concerns. I have been trying to avoid rituximab since the advent of the COVID-19 pandemic, but he is interested in exploring the possibility of lengthier remission. Is there anything about this patient and his disease that calls for the addition of rituximab?

How would you respond? Email us at ashclinicalnews@hematology.org.


Disclaimer: ASH does not recommend or endorse any specific tests, physicians, products, procedures, or opinions, and disclaims any representation, warranty, or guaranty as to the same. Reliance on any information provided in this article is solely at your own risk.

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