Paediatric Haematology: Decoding the full blood count (Hb and RBC)

With thanks to Dr Alexandra Briscoe and Professor Irene Roberts for their collaborative work.

The red cell count and haemoglobin (see February 2017 newsletter for normal ranges)

The red cell count is the actual number of red cells per mL of blood, and the haemoglobin (Hb) is the concentration of the Hb protein itself- the oxygen carrying protein.

A raised red cell count due to increased production of red cells is seen in children with chronic hypoxia, such as congenital heart disease and, in neonates, manifests as neonatal polycythaemia, usually due to chronic in utero hypoxia.

During the last 2 months of pregnancy erythropoiesis occurs at a rate of 3-5 x that of adults, consequentially the healthy newborn has a relative polycythaemia compared to infants and children-  manifest as a raised Hb, red cell count and haematocrit.

The Hb falls over the first 2-3 months of life in response to several factors- with the onset of respiration at birth- oxygenation increases, erythropoieitin production and erythropoiesis is decreased via negative feedback. Neonatal red blood cells have a shorter half-life of 90 days compared to 120 days for red cells in healthy children and adults. In addition over this time period, neonates undergo  rapid growth and weight increase with a subsequent increase in circulatory volume- leading to relative haemodilution. This physiological anaemia requires no intervention in otherwise healthy term infants and will rarely fall below 90g/L.

In contrast, infants born extremely prematurely at <28 weeks of completed gestation, will frequently require red cell transfusion. This is due to anaemia of prematurity. The cause is multifactorial, including low erythropoietin, shortened red cell lifespan, nutritional deficiency and iatrogenic blood letting, however the nadir in Hb occurs earlier (4-8 weeks compared to 8-12 weeks in term babies) and is more severe. Premature red blood cells have a life span of 35-50 days, and infants have a circulating blood volume of 90- 105 mls/kg, which could be as little as 45mls in a 24 week 500g infant. In addition, these infants do not receive maternal iron transfer via the placenta. Preterm infants also have a slow erythropoietin response to hypoxia and anaemia- this is because the site of production of erythropoietin is the liver rather than the kidney as per term infants. There is also evidence of increased metabolism of EPO in the preterm infant. (Strauss, 2010). Despite multiple studies into the use of exogenous erythropoietin for preterm infants, current guidelines recommend red cell transfusion for the management of anaemia of prematurity.


Ronald G. Strauss, Anaemia of prematurity: Pathophysiology and treatment, Blood Reviews, Volume 24, Issue 6, November 2010, Pages 221-225, ISSN 0268-960X,


January 2017 uploaded!

January 2017 brings the second part of information on gangs, the start of a series on urinalysis (specific gravity this month), an update on resus council guidelines and a link to expressing breastmilk.  Do leave comments below.

2 months in one for Nov/Dec 2016

First part of information on gangs this month, plus HbA1c units compared, last bit on orthopaedic feet, a warning about phenytoin overdose and a couple of links to good relevant courses.  Do leave comments below:

October 2016 PDF digest

Modern slavery this month in the safeguarding slot, O2 saturations in bronchiolitis, CHAT headache courses and some useful tables from Diabetes UK on diagnosis and management of diabetes.  Do leave comments below:

September 2016 uploaded

The value of PEWS this month, NICE on diabetes, a round up of former articles of use to the new batch of trainees and content from the paediatric orthopaedic team on funny shaped toes.  Do leave comments below.

August 2016 uploaded

Sepsis and the “in-betweeners” this month.  How to categorise the unwell children you are just not quite sure about.  Also testing in malaria, the new NHSGo app and cardiac assessment prior to starting medications for ADHD.  Do leave comments below:

July 2016 PDF added

Malaria this month, sexual exploitation, sepsis, prolonged jaundice and DDH.  Do leave comments below:

Diagnosing malaria in children

In children with suspected malaria do we need three negative blood films to exclude a diagnosis of Malaria?

-          with thanks to Dr Tom Waterfield for summarising his recent article (5) below for Paediatric Pearls


There are over 300 new cases of imported paediatric malaria in the UK each year and cases of imported malaria here have been increasing over the last 20 years (1).  Malaria in children is particularly difficult to diagnose because the initial presenting features are subtler than in adults.  Children may appear quite well initially with a fever and no focus but; they are at risk of a rapid deterioration and are more likely to develop severe malaria.

The “gold standard” for ruling out the diagnosis of malaria if clinically suspected is three negative thin and thick blood films (2).  This approach however, relies on serial phlebotomy and the availability of adequately trained staff.  Furthermore, during out-of-hours periods the time and resources required are likely to result in delays in obtaining results especially if trained staff have to come in from home.  There are now a range of Rapid Diagnostic Tests (RDTs) that are highly specific and sensitive for malaria. So are three films really required when we have RDTs?


There is only one study exploring the combination of blood films together with RDT’s in diagnosing imported malaria and it was in adults (3).  Of the 388 cases, 367 (95%) were diagnosed by the initial blood film. Of the 21 that weren’t diagnosed on the blood film 19 had RDT’s performed. This diagnosed a further 10 leaving only 9 cases (2.3%) not picked up by a single blood film and RDT. Only one case of P.falciparum infection was missed and this was in a partially immune individual who had already received an unspecified treatment. The remaining 8 missed cases were P.vivax and P.ovale.


If we extrapolate from this study, then if a single blood film and RDT are negative a diagnosis of malaria is extremely unlikely.  This is especially true in cases of suspected P.falciparum in a non-immune patient who has not received any treatment. The most obvious criticism here, is that it is difficult to extrapolate adult data and draw conclusions relating to children.  However, the available data comparing parasite counts between children and adults suggests that on average children have a comparable or higher parasite count than adults (4). This would suggest that the results seen for adults would be comparable or even favourable in children.


Because of the paucity of data overall and lack of paediatric data it is not possible to make a blanket recommendation.  The risk of malaria in each individual needs to be considered in conjunction with investigation results.  For more information on diagnosing malaria in children read – How to interpret malaria tests (5).




1.         Ladhani S, Garbash M, Whitty CJ, Chiodini PL, Aibara RJ, Riordan FA, et al. Prospective, national clinical and epidemiologic study on imported childhood malaria in the United Kingdom and the Republic of Ireland. Pediatr Infect Dis J. 2010;29(5):434-8.


3.         Pasricha JM, Juneja S, Manitta J, Whitehead S, Maxwell E, Goh WK, et al. Is serial testing required to diagnose imported malaria in the era of rapid diagnostic tests? Am J Trop Med Hyg. 2013;88(1):20-3.

4.         Mascarello M, Allegranzi B, Angheben A, Anselmi M, Concia E, Lagana S, et al. Imported malaria in adults and children: epidemiological and clinical characteristics of 380 consecutive cases observed in Verona, Italy. J Travel Med. 2008;15(4):229-36.

5.          Dyer E, Waterfield T, Eisenhut M. How to interpret malaria tests. Arch Dis Child Educ Pract Ed. 2016 Apr;101(2):96-101. doi: 10.1136/archdischild-2015-309048. Epub 2016 Feb 2.


June 2016 published

Curly toes this month to herald the start of a new series on paediatric orthopaedics, sexual bullying, jaundice in the neonatal period and periorbital cellulitis.  Do leave comments below…

Periorbital and orbital cellulitis in children

                         Peri-Orbital and Orbital Cellulitis in Children

With thanks to Dr Kat Smith, paediatric registrar and education fellow at King’s College Hospital….

The somewhat red, somewhat swollen eye is a relatively common presentation in children, and distinguishing between peri-orbital and orbital cellulitis hinges closely on an examination which can be difficult to perform in young children who cannot communicate pain on eye movement or subtle changes in vision.

Back to basics

orbital cellulitis diagram

(Diagram above from

The orbital septum is key in differentiating between peri-orbital and orbital cellulitis, and in dictating management. For those of us who haven’t thought about it since medical school, it is an extension of the periosteum of the frontal plate of the upper eyelid; a tough structure, where infection cannot pass from front to back unless the septum is breached by a sharp object. However, the orbital septum is not as thick and well developed in infants as it is in older children and adults, and so is not as effective a physical barrier in this age group.

Peri-orbital (or pre-septal) cellulitis is inflammation and infection of the eyelid soft tissue superficial and anterior to the orbital septum; the septum itself is not affected. Ocular function remains intact.

Orbital (or post-septal) cellulitis is infection of muscles and fat within the orbit, posterior to the orbital septum; the septum itself can be affected. It’s location in muscles and fat leads to associated ocular dysfunction.


What’s different in children?

Children are twice as likely to develop periorbital and orbital cellulitis in comparison to adults, and whilst in adults peri-orbital cellulitis is usually secondary to a superficial injury, children may develop it secondary to an occult underlying bacterial sinusitis (in particular, through the thin and porous ethmoid bone; there is often a history of recent URTI) or due to spread from another primary infection, such as pneumonia.

This difference in underlying aetiology means that in children a peri-orbital infection can rapidly progress to the much more concerning condition of orbital cellulitis, with the associated risk of rare but serious complications such as abscess formation, cavernous sinus thrombosis, intracranial abscess, and loss of vision.



The happy, well-looking child who is able to open their eye sufficiently for you to demonstrate normal light reflexes and see that they comfortably move their eyes in all planes more than likely has peri-orbital cellulitis; this will be most children. However, there are red flags that make orbital cellulitis a likely diagnosis and should prompt urgent referral to secondary care:

-          Eyelid swelling such that the eye is not visible

-          Toxic / systemically unwell

-          CNS signs or symptoms

-          Severe / persistent headache

-          Pain on pressing the closed eyelid, indicating septal involvement

-          Pain on eye movement, indicating involvement of muscle and / or fat

-          Diplopia; older children should be able to describe “seeing double”, younger children may become unsteady when walking or struggle to grab objects

-          Reduced visual acuity; the younger child may struggle to play with smaller / more “fiddly” toys

-          Proptosis

-          Ophthalmoplegia

-          Absent light reflexes

-          No improvement or worsening despite 48hrs oral antibiotics

-          Neonatal age group (may be congenital dacryocystitis)



Most children will be well, with mild-moderate swelling and erythema and no red flags; these children can initially be managed in the community, and most will not require later referral to secondary care.

Children with mild-moderate eyelid swelling, no significant erythema and an obvious cause – such as a chalazion or insect bite – do not have peri-orbital cellulitis, although they may need advice or treatment for the underlying cause such as warm compresses or anti-histamines.

Those with mild to moderate swelling, erythema and no obvious cause but no red flags are likely to have peri-orbital cellulitis and so require oral antibiotics; typically a 5-7 day course of co-amoxiclav is given, although this varies dependent on local microbiology guidance. Because of the underlying aetiology of peri-orbital cellulitis in children, parents should be advised that if children develop any red flag symptoms they require immediate medical review, and a GP review should be arranged for 48 hours’ time to ensure that symptoms have started to improve.

It can be unclear in young children if they have any red flags; if in doubt, refer to secondary care for review by ophthalmology, A&E, or paediatric teams. Even in secondary care it can be unclear, and children may be admitted simply for oral antibiotics and observation.  ENT teams will also need to be involved if orbital cellulitis is suspected.

As above, children with any red flags are likely to have orbital cellulitis and will likely require admission to hospital for blood tests, cultures and IV antibiotics +/- imaging of the sinuses and orbits (although more extensive neuroimaging is indicated if there is a suspicion of cerebral infection).


“Children are twice as likely to develop periorbital and orbital cellulitis in comparison to adults”

Robinson A, Beech T, McDermott A, et al. Investigation and Management of adult periorbital or orbital cellulitis. J Laryngol Oto. 2007;121:545-7.


BMJ Best Practice: Peri-orbital and orbital cellulitis. Available from

Clarke W. Periorbital and orbital cellulitis in children. Paediatr Child Health. 2004;9(7):471-2

The College of Optometrists. Clinical Management Guidelines. Cellulitis, preseptal and orbital. Available from