MCV- Mean Corpuscular Volume. (with thanks to Dr Xanna Briscoe and Prof Irene Roberts)

A measure of the size of the red blood cells.

Raised MCV- macrocytosis– may occur with or without anaemia. Physiological macrocytosis in the absence of anaemia occurs in neonates, especially those with Down syndrome, and during pregnancy.

Macrocytic anaemia- may be secondary to nutritional deficiencies in B12 and Folate leading to ineffective or abnormal erythropoiesis. This is easily diagnosed using simple blood tests. Where deficiency is excluded bone marrow examination may be required to identify rare causes such as myelodysplasia or Fanconi anaemia.

There are several drugs that may lead to macrocytosis, some of which are commonly used in the paediatric population. These include several chemotherapeutic agents, antibiotics and antiviral medications. It is also seen in congenital heart disease, hypothyroidism and Down Syndrome.

Additional investigations- guided by the history. It is important to check a reticulocyte count if a macrocytic anaemia is discovered. Reticulocytes are immature erythrocytes- which are large, and indicate increased erythropoiesis. Chronic reticulocytosis may falsely elevate the MCV. The absence of a raised reticulocyte count in the presence of severe anaemia suggests an inability of the bone marrow to produce red cells, eg due to inherited or acquired red cell aplasia.

Kaferle, Joyce, and Cheryl E. Strzoda. “Evaluation of macrocytosis.” American family physician 79.3 (2009).

Microcytosis– small red blood cells. Typically seen in iron deficiency anaemia; in the paediatric population at different ages the cause differs. In younger children and toddlers lack of supplementation may lead to deficiency. This is a particular issue in those that drink large volumes of cows milk as a substitute for iron containing foods. The main differential diagnosis is beta- or alpha-thalassaemia trait. Measurement of serum ferritin is the most useful test to identify iron deficiency- this will be low in iron deficiency and normal in beta- or alpha-thalassaemia trait.

In adolescence the pubertal growth spurt, and menorrhagia may be a causative factor. Further investigation will aid in determining the causes of microcytic anaemia (see below).

W Owen Uprichard, James Uprichard. Investigating microcytic anaemia. BMJ 2013;346:f3154

As published in April 2017 Paediatric Pearls newsletter…..

Source: http://www.fpnotebook.com/HemeOnc/Lab/MnCrpsclrVlm.htm

MCV is expressed in femtoliters = 10^-15 liters

MCV cutoffs vary by age and by lab reference

MCV Normal Range:

• Newborn: 95 to 121 fl
• Ages 6 months to 2 years: 70 to 86 fl
• Ages 12 to 18 years
• Boys: 78 – 98
• Girls: 78 – 102
• Age over 18 years: 78 to 98 fl

MCV Cutoffs for Microcytic Anemia:

• Age 1-2 years: <77 fl (CDC)
• Age 3-5 years: <79 fl (CDC)
• Age 6-11 years: <80 fl (CDC)
• Age 12-15 years: <82 fl (CDC)
• Age >15 years: <85 fl (CDC)
• Recommended adult microcytic MCV cutoff varies

Some sources advocate MCV <78 and others <82

So, you’ve got the FBC back and it shows microcytic anaemia.  How can you work out which of the above factors is causative?

If you only asked for FBC and the child is more than 6 months old, try this:

Therefore a child of 6 months or older with hypochromic, microcytic anaemia with an increased RDW has presumed iron deficiency.  They could have thalassaemia trait as well….

If you asked for other tests or are at liberty to repeat the blood test, here are some suggested extra investigations and their interpretation:

Part 2 of “Decoding the full blood count” with thanks to Dr Alexandra Briscoe, paediatric registrar at Whipps Cross University Hospital, and Professor Irene Roberts, professor of paediatric haematology at Oxford.

Haematocrit/packed cell volume

Haematocrit/ packed cell volume- the proportion of blood that is made up of cells (not plasma); it is measured as a percentage or fraction.

Low haematocrit is seen in anaemia, though it will not tell you the direct cause for the anaemia.

Raised haematocrit is seen in polycythaemia, in the newborn infant this is termed Neonatal Polycythaemia.

Defined as a venous haematocrit > 65%, occurring in 0.4-5% of healthy newborns. Symptoms are believed to be due to hyperviscosity. On examination children appear plethoric, and may have multi-systemic symptoms. These include- CNS features of irritability, cerebrovascular accidents and seizures. Apnoea and respiratory distress occur as a result of decreased pulmonary blood flow. In addition infants may demonstrate poor feeding, and may in rare cases develop necrotising enterocolitis (NEC.) Renal effects include renal vein thrombosis, oliguria, proteinuria and haematuria.  Hypoglycaemia and thrombocytopenia (Vlug, 2013) are also seen commonly.

The development of polycythaemia occurs secondary to increased erythropoiesis as a consequence of chronic fetal hypoxia. IUGR and placental insufficiency- due to post-dates pregnancies, pre-eclampsia and maternal smoking, increase the incidence of polycythaemia. Infants of diabetic mothers, those with Beckwith –Weidemann, and congenital thyrotoxicosis are also at increased risk.

There has been much debate as to whether delayed cord clamping increases the incidence of polycythaemia. Current NICE guidelines recommend cord clamping between 1-5 minutes after delivery, provided there is no concern regarding the infant’s heart rate or need for resuscitation. In a Cochrane review of cord clamping practices and neonatal outcomes in 2013 McDonald et al found that delayed cord clamping was associated with increased risk of jaundice requiring phototherapy, however beneficial outcome in terms of iron stores- with a 50% reduction in iron deficiency at 3-6 months. They reported no difference in incidence of polycythaemia in 5 trials measuring this outcome.

Current management of symptomatic polycythaemia is a partial exchange transfusion.

Vlug RD, Lopriore E, Janssen M, et al. Thrombocytopenia in neonates with polycythemia: incidence, risk factors and clinical outcome. Expert Rev Hematol. 2015 Feb. 8 (1):123-9. [Medline].

ID: CD004074 McDonald, Susan J, Middleton, Philippa, Dowswell, Therese Morris, Peter S

Effect of timing of umbilical cord clamping of term infants on maternal and neonatal outcomes

Cochrane Database of Systematic Reviews 2013

DOI: 10.1002/14651858.CD004074.pub3

US: http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD004074.pub3/abstract

What are normal haematocrit levels?

(taken from http://www.medicinenet.com/hematocrit/page2.htm)

The normal ranges for haematocrit  depend on the age and, after adolescence, the sex of the individual. The normal ranges are:

• Newborns: 55% to 68%
• One (1) week of age: 47% to 65%
• One (1) month of age: 37% to 49%
• Three (3) months of age: 30% to 36%
• One (1) year of age: 29% to 41%
• Ten (10) years of age: 36% to 40%
• Adult males: 42% to 54%
• Adult women: 38% to 46%

These values may vary slightly among different laboratories.