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Savez-vous à quelle maladie correspond le cas de ce mois-ci? Testez vos connaissances avec le quiz ci-dessous!

Quelle pathologie conduit à cet hémogramme anormal? Échantillon normal mais erreur pré-analytique
Sarcome à cellules de Kupffer, sous chimiothérapie
Cirrhose due à l’abus d’alcool
Carence en vitamine B12 ou folates

Version en ligne de note cas mensuel

La bonne réponse du quiz du mois de mai est:

Normal blood sample but incorrect sample handling

Scattergrammes et Cytologie

Patient history: a blood sample was taken from a 38-year old male patient for routine follow-up.

Tableau

Diagnostic différentiel et interprétation

The answer can be inferred from…

  •  Increased MCV
  • Normal MCH
  • Decreased MCHC
  • Increased MacroR and a normal reticulocyte count

 

Case history

A 38-year old male turned to his family doctor for a routine follow up.

Case results

The reported haemogram showed mostly normal results, except for the RBC indices: the erythrocyte volume (MCV) and haematocrit (HCT) were increased, while the mean corpuscular haemoglobin concentration (MCHC) was decreased. A decreased MCHC can be caused either by a decreased mean cellular haemoglobin content (MCH) or an increased MCV, which was the case in this haemogram. Therefore, it was important to establish the cause of the increased MCV. Since MCV is calculated from HCT and the RBC count (MCV = HCT / RBC), an increased MCV is caused either by an increased HCT or a decreased RBC count. The RBC count of the presented patient showed a normal value so the cause for the increased MCV was the elevated HCT.

A   decreased MCHC, in this case caused by an increased erythrocyte volume with a normal content of haemoglobin, is only possible in some rare situations (Figure 1):

a) Treatment of anaemia patients with erythropoiesis stimulating agents such as erythropoietin (EPO) leads to a reticulocytosis which can lead to an increased MCV because reticulocytes are larger than mature erythrocytes. Together with an inadequate iron supply, this would result in a functional iron deficiency and the production of erythrocytes with a low MCHC. However, functional iron deficiency would also lead to a higher percentage of microcytes (MicroR) or hypochromic cells (HYPO-He), which was not observed in this case. This could be excluded because an EPO-associated reticulocytosis was absent.

b) The second reason for an increased MCV can be ageing of a sample. In vitro metabolism leads to changes in plasma osmolarity, which causes an increased RBC volume (1). The MCH is not changed in such a situation, and HYPO-He is not increased. Therefore, the reason for this abnormal haemogram was incorrect sample handling/aged sample.

 

The following answers are incorrect for the described reasons

Kupffer cell sarcoma, under chemotherapy

Chemotherapy of malignant diseases, which targets cells in the division phase, can cause an increased MCV without changing the haemoglobin content (normal MCH); this would result in a decreased MCHC. Besides the decreased MCHC or increased MCV, chemotherapy would also result in a low RBC count and an anaemia with a decreased reticulocyte count. As in this case these parameters are all normal, Kupffer sarcoma under chemotherapy can be excluded as a possible diagnosis.

Liver cirrhosis due to alcohol abuse

Excessive alcohol abuse affects erythropoiesis in the bone marrow, which leads to decreased mitosis of RBC progenitors, similar to the effect of vitamin B12 and B6 deficiency (2). This often results in the generation of macrocytic RBC with an increased haemoglobin content (increased MCH and HYPER-He). However, the total count would be reduced (low RBC) and MCHC would be normal. As this is not the case in the observed example, alcohol abuse can be excluded as a possible diagnosis.

 

Vitamin B12 or folate deficiency

Cobalamin (vitamin B12) and folate deficiencies impair DNA synthesis, which leads to reduced cell division (abnormal mitosis) of red blood cells (3). This results in the generation hyperchromic macrocytic RBC, characterised by increased MCV, MacroR and Hyper-He%. In this case, indeed, increased MCV and MacroR are observed. However, in the absence of hyperchromic cells, decreased RBC counts, increased MCH with a normal MCHC, these parameters do not support the diagnosis of vitamin B12 or folate deficiency.

Maladie sous-jacente

Aged samples

Storage of EDTA blood samples at room temperature or under insufficient cooling conditions leads to ageing of the blood. The pH in the sample and osmotic pressure in the cells change, leading to the loss of elasticity of cellular membranes and swelling of red blood cells (MCV increases and MCHC decreases as a result). Irreversible changes in leucocyte populations occur already within the first hours of storage. So, granulocytes degranulate and undergo cytoplasmic and nuclear vacuolization. Their membrane properties change, therefore altering the reaction with the staining reagent of a haematology analyser. This leads to abnormal shapes of the WBC populations in the WNR and WDF scattergrams. Wrong flagging due to the effects in the aged samples is a problem of haematology analysers from all manufacturers. Increase in the number of false positive flags leads to increased rate of smear review, therefore affecting the workflow in the lab (1). With the Aged sample software, Sysmex provides a solution for the labs which may receive a higher number of aged samples.

 

 

The ‘Aged Sample Identifier’ software

Samples with decreased MCHC and abnormal white blood cell populations in the WDF scattergram are suspected as aged. Abnormal shapes of WBC populations of an aged sample may cause a false positive ‘Blasts/Abn Lympho?’ flag from the WDF channel. However, since leukaemic and reactive white blood cells in a non-aged sample show increased fluorescence levels (4), the ‘Aged Sample Identifier’ software is able to differentiate between a correct and incorrect ‘Blasts/Abn Lympho?’ flag. Therefore, the algorithm is able to detect whether the abnormal scattergram of a sample is due to a real pathology or due to ageing of the sample.

A study demonstrated (1) that the ‘Aged Sample Identifier’ software reduces the rate of unnecessary smear reviews by 23% when implemented in the laboratory routine. Besides, in the XN analysers equipped with WPC channel, the ‘Aged Sample Identifier’ software can prevent reflex measurements with the WPC channel, thus saving the cost of the reagent.

Bibliographie

  1. Ulset RA, Petrasch E, Saker J et al. (2014): "Aged sample" software on automated routine hematology analyzer enables differentiation between pathological and non-pathological WBC flagging in aging samples. Clin Lab. 60(12):1961-1968
  2. Gonzalez-Casas R, Jones EA, Moreno-Otero R. (2009): Spectrum of anemia associated with chronic liver disease. World J Gastroenterol. 15(37):4653-4658
  3. Clarke R, Grimley Evans J., Schneede J., et al (2004): Vitamin B12 and folate deficiency in later life. Age und Ageing, 33, p. 34–41
  4. Kawauchi S, Kono M, Takagi Y et al. (2013): The positions of normal leukocytes on the scattergram of the newly developed abnormal cell-detection channel of the XN-Series multi-parameter automated hematology analysers. Sysmex Journal International Vol 23(1)

 

 

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