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