Use 0.9% saline (not albumin or plasma), target Hct approximately 50%, exchange in small aliquots, monitor continuously, and repeat Hct approximately 4 hours after the procedure.
| Term | Practical Definition | Clinical Meaning |
|---|---|---|
| Polycythemia | Increased red-cell mass; operationalized as venous Hct ≥65% or Hb >22 g/dL in term infants. | A laboratory diagnosis that increases the probability of hyperviscosity, but not every infant with Hct ≥65% is symptomatic. |
| Hyperviscosity syndrome | A clinical perfusion syndrome caused by thickened blood and microvascular sludging, sometimes with thrombosis. | The infant may have respiratory, neurologic, renal, metabolic, gastrointestinal, or hematologic signs. |
| Relative hemoconcentration | A high Hct from plasma-volume contraction — especially dehydration — without true increased red-cell mass. | Rule out dehydration and inadequate intake before labeling the infant as true polycythemia. |
| Partial exchange transfusion (PET) | Isovolemic hemodilution: remove blood while replacing the same volume with 0.9% saline to lower Hct. | A procedure for selected infants — not routine treatment for every elevated Hct. |
Treat the baby, not the number. A venous Hct of 66% in a vigorous, feeding, asymptomatic infant is different from Hct 66% with persistent hypoglycemia, respiratory failure, seizures, oliguria, or thrombosis. The decision for PET should be individualized, but the threshold should be high in asymptomatic infants because long-term benefit has not been proven.
| Mechanism | Bedside Consequence | What to Monitor |
|---|---|---|
| Rising Hct increases viscosity nonlinearly, especially once Hct reaches approximately 65%. | Blood flow through small vessels slows, vascular resistance rises, and tissue oxygen delivery can fall despite a high oxygen-carrying capacity. | Perfusion, capillary refill, oxygenation, respiratory work, lactate if ill, and mental status. |
| Microvascular sludging and low-flow states can affect brain, kidney, lung, gut, and skin. | Symptoms may be nonspecific: lethargy, irritability, tremor, apnea, cyanosis, tachypnea, poor feeding, or seizures. | Neurologic exam, urine output, respiratory support needs, feeding tolerance, and signs of thrombosis. |
| Increased red-cell mass increases bilirubin load and may coexist with platelet consumption. | Hyperbilirubinemia and thrombocytopenia are common associated abnormalities. | TSB/direct bilirubin when indicated, platelet count, DIC work-up if clinically ill. |
| Polycythemia commonly reflects fetal adaptation to chronic hypoxemia or passive placental transfusion. | The cause may identify additional risks: IUGR, diabetic fetopathy, twin-to-twin transfusion, congenital heart disease, or trisomy 21. | Maternal history, growth status, cord timing, twin status, cardiac exam, oxygen saturation, and dysmorphology. |
| Category | Examples | Clinical Note |
|---|---|---|
| Increased fetal erythropoiesis | IUGR/SGA, chronic placental insufficiency, maternal hypertension/preeclampsia, high altitude, post-term infant, perinatal hypoxia/asphyxia. | These infants may have increased nucleated RBCs or reticulocytosis from chronic fetal hypoxemia. |
| Maternal or fetal metabolic risk | Infant of diabetic mother, LGA infant, neonatal hypoglycemia. | Hypoglycemia can be a symptom, a comorbidity, or a reason to screen when persistent or severe. |
| Passive transfusion | Twin-to-twin transfusion recipient, TAPS recipient, excessive placental transfusion, excessive delayed cord clamping, cord milking toward the infant. | History of monochorionic twins or delivery-room placental transfusion details can explain the Hct pattern. |
| Genetic or congenital conditions | Trisomy 21, Beckwith-Wiedemann syndrome, cyanotic congenital heart disease, renovascular malformations, congenital adrenal hyperplasia. | Look for associated disease rather than treating the Hct in isolation. |
| Relative hemoconcentration | Dehydration, poor intake, weight loss, hypernatremia, fever, or diuresis. | Repeat clinical hydration assessment and consider a venous Hct after fluids if the presentation suggests hemoconcentration. |
| System | Symptoms/Signs That Support Checking Hct | High-Concern Findings |
|---|---|---|
| Cardiorespiratory | Cyanosis, tachycardia, tachypnea, respiratory distress, PPHN, oxygen lability. | Severe or persistent respiratory distress not responding to routine care, pulmonary hypertension, or unexplained hypoxemia. |
| Neurologic | Lethargy, irritability, tremor, jitteriness, abnormal cry, hypotonia, apnea, seizures. | Seizure, encephalopathy, stroke, or venous thrombosis. |
| Metabolic | Hypoglycemia, especially recurrent or persistent hypoglycemia. | Hypoglycemia requiring high GIR, rapid escalation, or central access. |
| Gastrointestinal | Poor feeding, vomiting, abdominal distension, blood in stool, feeding intolerance. | Concern for NEC, bowel ischemia, or severe intolerance. |
| Renal | Oliguria/anuria, hematuria, hypertension, renal vein thrombosis signs. | Hematuria with flank mass, thrombocytopenia, renal impairment, or suspected thrombosis. |
| Hematologic / skin | Plethora, delayed capillary refill, hyperbilirubinemia, thrombocytopenia, DIC. | DIC, severe thrombocytopenia, or bilirubin near treatment thresholds. |
Risk factors alone are not an indication for routine Hct screening in a clinically well infant (UCSF NCNC consensus). A symptom-based strategy reduces unnecessary heel sticks, false-high capillary values, anxiety, NICU admission, and unnecessary PET.
| Step | Action | Reason |
|---|---|---|
| 1 | Assess symptoms, perfusion, respiratory status, feeding, hydration, glucose, bilirubin risk, urine output, and neurologic status. | Polycythemia is clinically important when it is causing or contributing to hyperviscosity physiology. |
| 2 | If using a capillary heel-stick Hct as a screen, confirm an elevated result with venous or arterial Hct before treatment. | Capillary values can be 5–15% higher than venous values and can lead to overtreatment. |
| 3 | Base treatment decisions on venous or arterial Hct, not capillary Hct. | Published thresholds and procedure recommendations are built around confirmatory Hct measurement. |
| 4 | Check glucose immediately and treat hypoglycemia using the neonatal hypoglycemia pathway. | Hypoglycemia is common and may be clinically more urgent than the Hct number. |
| 5 | Order targeted labs when indicated: CBC with platelets, bilirubin, blood gas/lactate if ill, calcium, electrolytes, renal function, coagulation tests, and culture if sepsis is in the differential. | Laboratory abnormalities may include hypoglycemia, hypocalcemia, hyperbilirubinemia, thrombocytopenia, reticulocytosis, and increased nucleated RBCs. |
| 6 | Evaluate the cause: maternal diabetes, IUGR/SGA, LGA, twins, delayed cord clamping, hypoxia/asphyxia, congenital heart disease, trisomy 21, and dehydration. | The underlying diagnosis drives monitoring, follow-up, and recurrence counseling. |
| Result | Interpretation | Recommended Action |
|---|---|---|
| Capillary Hct >65% | Screen only | Possible polycythemia, but heel-stick Hct may overestimate venous Hct. Confirm with venous or arterial Hct if symptoms are present or if treatment is being considered. |
| Venous/arterial Hct <65% | Threshold not met | Polycythemia threshold not met by standard definition. Look for other causes of symptoms: sepsis, respiratory disease, hypoglycemia, cardiac disease, neurologic disease, or dehydration. |
| Venous/arterial Hct 65–70% | Polycythemia — symptoms determine urgency | Hydrate if needed, treat hypoglycemia, monitor symptoms, repeat Hct based on clinical evolution. PET only if symptomatic after senior review. |
| Venous/arterial Hct >70–75% | Higher risk — senior review | Senior review; manage hydration and comorbidities. PET usually reserved for symptomatic infants or selected persistent/asymptomatic Hct >75%. |
| Venous/arterial Hct >75% | Severe — consider PET | Consider PET even if asymptomatic, but counsel that evidence for benefit in asymptomatic infants is limited. Individualize after senior neonatologist review. |
| Step | Action |
|---|---|
| Step 1 | Stabilize ABCs, check glucose, assess perfusion and hydration, and identify symptoms compatible with hyperviscosity. |
| Step 2 | Obtain venous or arterial Hct if symptoms are present, capillary Hct is high and treatment is being considered, or high-concern signs exist. |
| Step 3 | If Hct <65%: stop the polycythemia pathway and investigate other causes of symptoms. |
| Step 4 | If Hct ≥65% and infant is asymptomatic: provide feeding/hydration support and observation. Do not perform PET if Hct ≤75%. |
| Step 5 | If Hct >65% and symptoms are compatible with hyperviscosity: call neonatologist, treat comorbidities, and consider PET. |
| Step 6 | If Hct >75% and infant is asymptomatic: discuss with senior neonatologist — PET may be considered, but evidence for benefit is limited. |
| Step 7 | After PET or conservative treatment: reassess symptoms, glucose, hydration, bilirubin risk, and urine output; repeat Hct approximately 4 hours after PET. |
| Clinical State | Hct Value | Recommended Action |
|---|---|---|
| Asymptomatic | Venous Hct <65% | No polycythemia treatment; continue routine care unless other clinical issues exist. |
| Asymptomatic | Venous Hct 65–75% | Do not perform PET; ensure adequate feeding/hydration and follow symptoms and bilirubin/glucose as clinically indicated. |
| Asymptomatic | Venous Hct >75% | Consider senior neonatologist review and possible PET; evidence of benefit is minimal, so decision should be individualized and local-policy guided. |
| Symptomatic | Venous Hct >65% | Consider PET after senior review, especially if symptoms are significant, persistent, or not explained by another diagnosis. |
| Symptomatic but unstable | Any Hct ≥65% with shock, severe respiratory disease, seizure, thrombosis, or severe hypoglycemia | Stabilize first, treat immediately reversible problems, consult neonatology/transport/hematology as needed, and consider PET when safe and indicated. |
Volume (mL) = [(Initial Hct − Desired Hct) ÷ Initial Hct] × Weight (kg) × 90 mL/kg
Target Hct = 50% · Calculated volume typically 20–40 mL/kg in term infants · Replace with 0.9% saline only
| Procedure Element | Recommended Practice | Safety Reason |
|---|---|---|
| Consent and team | Obtain informed consent, call senior neonatologist, and ensure staff are experienced with neonatal vascular access and stopcock technique. | PET has procedure risks including bleeding, thrombosis, infection, catheter complications, air embolism, and limb ischemia. |
| Access | Use the safest available access per local policy: UVC, UAC, or peripheral arterial withdrawal with simultaneous peripheral IV saline infusion. | A simultaneous method can reduce large intravascular swings but may be technically harder. |
| Fluid | Replace removed blood volume with an equal volume of 0.9% saline. | The procedure is isovolemic hemodilution, not a blood-product exchange. Protein-containing fluids (albumin, plasma) may increase viscosity. |
| Aliquot size | Withdraw and replace in small aliquots — commonly 5 mL/kg per cycle. | Small aliquots reduce rapid hemodynamic shifts and make the procedure easier to monitor. |
| Monitoring | Continuous cardiorespiratory monitoring, frequent temperature checks, perfusion checks, line checks, and glucose monitoring if unstable or hypoglycemic. | Hyperviscosity and the procedure can affect perfusion, glucose stability, catheter function, and temperature. |
| After PET | Repeat Hct approximately 4 hours after PET and reassess clinical symptoms, glucose, bilirubin, feeding, urine output, and line-related complications. | The goal is clinical improvement and a safer Hct — not just a lower number. |
| Example | Calculation | Interpretation |
|---|---|---|
| 3.5 kg infant, Hct 70%, target 50% | [(70 − 50) ÷ 70] × 3.5 × 90 = 90 mL total (~26 mL/kg) | Within the usual 20–40 mL/kg range. Proceed if symptomatic and senior-reviewed. |
| 4.0 kg infant, Hct 76%, target 50% | [(76 − 50) ÷ 76] × 4.0 × 90 = 123 mL total (~31 mL/kg) | Within the usual range, but the decision still depends on symptoms and senior review. |
| 2.5 kg infant, Hct 66%, target 50% — asymptomatic | [(66 − 50) ÷ 66] × 2.5 × 90 = 55 mL total (~22 mL/kg) | PET is not recommended at this Hct in an asymptomatic infant — calculation alone should not drive treatment. |
| Clinical Issue | Conservative Action | Escalation Trigger |
|---|---|---|
| Hydration / feeding | Support breastfeeding or enteral intake if safe; use IV fluids when intake is inadequate, infant is symptomatic, or dehydration/poor perfusion is present. | Persistent symptoms, rising Hct, hypernatremia, poor perfusion, or inability to feed safely. |
| Hypoglycemia | Treat using the local neonatal hypoglycemia pathway; do not attribute recurrent low glucose only to polycythemia. | High GIR requirement, rapid escalation, central line need, or persistent hypoglycemia should prompt Hct check and broader evaluation. |
| Jaundice | Monitor bilirubin according to gestational age, age in hours, hemolysis risk, and local/AAP/NICE treatment charts. | Rapidly rising bilirubin, early jaundice, exchange-level bilirubin, or suspected hemolysis. |
| Respiratory distress | Treat lung disease/PPHN using standard respiratory and oxygenation pathways while considering hyperviscosity as a contributor. | Severe or persistent respiratory distress unresponsive to routine therapies. |
| Renal perfusion | Follow urine output, blood pressure, hematuria, creatinine, and thrombocytopenia when renal thrombosis is possible. | Oliguria/anuria, hematuria, renal dysfunction, hypertension, or suspected renal vein thrombosis. |
| Neurologic symptoms | Check glucose, calcium, electrolytes, infection risk, neurologic exam, and consider imaging if seizure/stroke signs occur. | Seizure, encephalopathy, focal neurologic sign, apnea unexplained by other disease, or suspected thrombosis. |
| Problem | Why It Matters | How to Separate It |
|---|---|---|
| Dehydration / poor intake | Can cause relative hemoconcentration and worsen viscosity without true increased red-cell mass. | Weight loss, sodium, urine output, feeding history, physical hydration, repeat venous Hct after fluids if needed. |
| Hypoglycemia from IDM or metabolic disease | Hypoglycemia may be associated with polycythemia but may also be the primary diagnosis. | Glucose trend, GIR requirement, maternal diabetes history, ketones/insulin/cortisol/GH if persistent. |
| Sepsis or respiratory disease | Tachypnea, poor feeding, lethargy, and temperature instability are nonspecific. | Culture/antibiotic decision by sepsis risk, CXR/blood gas/oxygenation, response to respiratory care. |
| Cyanotic CHD / PPHN | Cyanosis and hypoxemia may coexist with polycythemia or be the underlying cause. | Pre/post-ductal saturations, echo when indicated, cardiac exam, perfusion, lactate. |
| Hemolysis / jaundice disorders | Polycythemia increases bilirubin load but hemolysis changes bilirubin risk and management. | DAT, blood type, retic, smear, G6PD when indicated, bilirubin trajectory. |
| Thrombosis | Hyperviscosity can be associated with cerebral or renal thrombosis. | Focal neurologic signs, seizures, hematuria, oliguria, thrombocytopenia, renal Doppler or neuroimaging when indicated. |
| Population | Practical Note |
|---|---|
| Infants <34 weeks GA | UCSF PET guidance is explicitly designed for infants ≥34 weeks. For more premature infants, use local NICU policy and senior neonatology/hematology input. |
| ELGAN / VLBW infants | Hyperviscosity syndrome is uncommon in preterm infants, but severe Hct elevation with symptoms should prompt careful evaluation for dehydration, transfusion exposure, placental events, and thrombosis. |
| Monochorionic twins | Recipient twin in TTTS or TAPS may have high Hct and should be assessed with the clinical context, co-twin status, and placental history. |
| Infant of diabetic mother | IDM infants may have polycythemia and hypoglycemia; glucose stability and feeding readiness require active management in parallel. |
| Trisomy 21 or Beckwith-Wiedemann syndrome | Polycythemia may be part of a broader phenotype; screen for associated cardiac, metabolic, airway, feeding, and genetic issues. |
| Delayed cord clamping history | Physiologic delayed cord clamping is usually beneficial, but excessive placental transfusion or cord stripping toward the infant can contribute to polycythemia. |
| Mistake | Why It Is Unsafe | Better Practice |
|---|---|---|
| Treating a heel-stick Hct without confirmation | Capillary Hct can overestimate venous Hct by 5–15% and may lead to unnecessary PET. | Confirm with venous or arterial Hct before treatment decisions. |
| Screening every risk-factor infant | Increases false positives, painful procedures, and downstream interventions without clear benefit. | Screen symptomatic infants and infants with high-concern findings. |
| Using PET for asymptomatic Hct ≤75% | Consensus guidance recommends against PET in this group; evidence does not support benefit and NEC risk may be increased. | Observe, hydrate/feed, and monitor clinically. |
| Ignoring hypoglycemia while focusing on Hct | Hypoglycemia can cause neurologic injury and may need immediate treatment. | Check and treat glucose early; prioritize it above the Hct number in the stabilization sequence. |
| Using albumin or plasma for PET | Protein-containing fluids may increase viscosity compared with saline. | Use 0.9% saline unless a specialist-directed exception exists. |
| Forgetting the underlying cause | Polycythemia may be a clue to IUGR, diabetes, twin transfusion, CHD, trisomy, hypoxia, or dehydration. | Document the cause and tailor follow-up accordingly. |
| Source | How to Interpret in This Chapter |
|---|---|
| Baylor 2025–2026 | Used as the ordering framework and to keep the topic inside the same chapter sequence as the rest of the guideline project. |
| UCSF NCNC 2023 | Most practical current open bedside source for screening and PET thresholds in infants ≥34 weeks; this chapter follows its symptom-based screening and PET threshold logic. |
| Merck Professional 2024 | Useful concise summary of definition, etiology, signs, diagnosis, and treatment principles — including the distinction between polycythemia and hyperviscosity. |
| Cochrane Neonatal Review | Important evidence caution: PET has no proven clinically significant long-term benefit in well/minimally symptomatic infants and may increase NEC risk. This finding should anchor the threshold for PET in asymptomatic infants. |
This is an educational guideline synthesis for Neonatology Academy. It is not a substitute for local NICU policy, laboratory reference methods, consultant judgment, transfer pathways, or bedside assessment of the individual infant. Medication doses, fluid rates, vascular-access procedures, PET technique, and monitoring intervals must be verified locally before clinical use.