Paediatrics: Polycythaemia

Polycythaemia

·  Traditionally, defined as an increase in the total red blood cell mass (RCM) above age-specific normal. As normal ranges of RCM are lacking in children, a raised haematocrit/packed cell volume (Hct/PCV) above age-specific normal is used instead.

·  Commonest in the newborn: exists when venous or arterial Hct >65%.

·  Polycythaemia-hyperviscosity syndrome is diagnosed in infants when Hct > 65–75% and usually requires partial exchange to reduce to 755%.

·  Very rare in childhood, but seen in teenagers with early onset myeloproliferative disorders, which should be suspected if Hct is raised > 3–4 SD above age specific mean.

Causes of polycythaemia

Neonatal causes

·  Hypertransfusion: delayed cord clamping, twin to twin transfusion syndrome, maternal–foetal transfusion

·  Endocrine: infant of a diabetic mother, CAH, neonatal thyrotoxicosis.

·  Chronic hypoxia: intrauterine growth retardation, placental insufficiency, high altitude

·  Maternal disease: pregnancy-induced hypertension, cyanotic heart disease

·  Syndromic: Down syndrome, Beckwith–Wiedemann syndrome

·  Relative polycythaemia: due to reduced plasma volume due to dehydration, diuretic therapy

Causes in older children

·  Primary: polycythaemia rubra vera (very rare)

·  High O₂ affinity polycythaemic Hb variant (familial polycythaemia)

·  Secondary to increased erythropoietin production:

·  Compensatory increase occurs in cyanotic CHD, severe chronic respiratory disease, chronic obstructive sleep apnoea, chronic alveolar hypoventilation, e.g. gross obesity, high altitude, abnormal Hb with high O₂ affinity

·  Inappropriately increased production with cerebellar haemangioblastoma, renal disease (renal cysts and carcinoma), hepatocellular carcinoma

·  Relative: dehydration or diuretic therapy

Presentation

·  Asymptomatic plethora occurs in most patients, particularly newborns.

·  Jaundice (newborn): due to increased red cell turnover.

·  Hypoglycaemia (newborn): due to increased red cell glucose consumption.

·  Hyperviscosity syndrome in newborns: hypotonia, congestive cardiac failure, tachypnoea, seizures, abnormal renal function and NEC.

·  CNS: cerebral irritability, seizures, strokes, cerebral haemorrhage.

·  Respiratory distress, pulmonary hypertension, e.g. PPHN.

Congestive cardiac failure.

·Thrombosis: e.g. renal venous thrombosis.

·Miscellaneous: cyanosis (PaO₂ usually normal), hepatomegaly.

Management

·Diagnosis is often obvious, e.g. cyanotic CHD.

·FBC: ‘rise’HCT, ‘rise’RCC, blood film.

·Exclude ‘fall’ serum glucose or calcium, or ‘rise’bilirubin (newborn).

·Investigate for cause if not obvious.

·In neonates; if symptomatic or PCV >70% perform partial (dilutional) exchange transfusion over 30min with normal saline (rather than donor derived plasma products) to reduce PCV to <60%.

Dilutional exchange volume (mL) =

blood volume x [(observed –desired Hct)/observed Hct]

Prognosis

Prognosis is generally good unless severe hypoglycaemia or thrombotic complications occur.