John A. Widness, MD
Peer Review Status: Internally Peer Reviewed


True whole blood viscosity cannot be routinely measured on blood samples. Viscosity increases with increasing central venous or arterial hematocrit, the diagnosis rests on the presence of polycythemia (hematocrit > 65%) and in the presence of clinical signs consistent with the diagnosis. This condition is almost always found in high risk infants during the first 24 hours of life.

High risk infants:

  • SGA infants
  • LGA infants
  • IDMs
  • Delayed cord clamping
  • Transfusions, e.g., twin-twin, maternal -> fetal
  • Trisomies, e.g., Down Syndrome, 13, & 18

Clinical signs of hyperviscosity:

  • Lethargy  
  • Hypotonia
  • Weak suck
  • Difficult to arouse
  • Irritable when aroused
  • Tremulousness
  • Seizures
  • Plethora
  • Tachypnea or respiratory distress
  • Abdominal distention


High risk infants who are asymptomatic for hyperviscosity should have a screening capillary hematocrit obtained at 4-6 hours of age. This allows equilibration of postnatal hematocrit following placental transfusion at delivery. Infants with symptoms consistent with hyperviscosity should be tested immediately.

  • Capillary hematocrit > 65% at 4-6 hours of life should be followed up immediately with a peripheral venous (or arterial) spun hematocrit.
  • Capillary hematocrits > 60% drawn before 4 hours of life should be repeated with a second capillary hematocrit at 4-6 hours of life.

Associated laboratory findings:

  • Abnormal chest X-ray: cardiomegaly, increased vascularity, hyperaeration, alveolar infiltrates, pleural effusions.
  • Thrombocytopenia
  • Hypoglycemia
  • Hyperbilirubinemia (not apparent for at least a day or two)

Associated clinical conditions attributable to hyperviscosity:

  • Increased pulmonary vascular resistance leading to pulmonary hypertension
  • Increased systemic vascular resistance
  • Increased myocardial strain
  • Hypoxemia
  • Pulmonary venous congestion
  • Decreased regional blood flow
    • Gut (NEC)
    • Kidney
    • Brain
    • Myocardium (CHF) 
  • Thromboses and gangrene
  • Increased glucose utilization
  • Local consumption of platelets


  • Treatment of the asymptomatic infant with a hematocrit between 65-70% is controversial.
  • Treatment of the symptomatic infant with partial exchange transfusion.

Exchange Volume mL

Estimated blood volume = 80-85 mL/kg; Hct desire = 50-55%

Estimated blood volume = 80-85 mL/kg; Hct desired = 50-55%;
Example: A 3.3 kg infant has a venous hematocrit of 72% and needs a partial exchange transfusion. You would like his post exchange Hct to be 50%:

Volume to be exchanged mL

Avoid push-pull technique through the UV catheter. To do so, remove blood through umbilical venous (or arterial if necessary) catheter while infusing an equal volume of normal saline at a similar rate through a peripheral vein. Many patients may require the same volume of normal saline to be given over an hour a 2nd time for tachycardia while their blood volume equilibrates.

  • The push-pull method has been associated with an increased risk of NEC.


Goldberg KE, Wirth FH, Hathaway WE, Guggenheim MA, Murphy JR, Braithwaite WR, and Lubchenco LO. Neonatal hyperviscosity II. effect of partial plasma exchange transfusion. Pediatrics 1982;69:419-425.

Gross GP, Hathaway WE and McGaughey HR. Hyperviscosity in the neonate. J Pediatr 1973;82:1004.

Hein HA and Lathrop SS. Partial exchange transfusion in term, polycythemic neonates: absence of association with severe gastrointestinal injury. Pediatrics 1987;80:75-78.

Oski FA, Naiman JL, Stockman III JA., and Pearson HA. Polycythemia and hyperviscosity in the neonatal period. In: M. Markowitz, ed. Hematologic Problems in the Newborn: Volume IV. Major Problems in Clinical Pediatrics (3rd ed.). Philadelphia: PA: Saunders, 1982:87-96.