Tests
1st tests to order
transcutaneous bilirubin (TcB)
Test
Screening test. Should be measured between 24 and 48 hours after birth (or before discharge if that occurs earlier) and as soon as possible in those noted to be jaundiced within 24 hours of birth.[7] TSB values are usually within 3 mg/dL of the transcutaneous value if the TSB is <15 mg/dL.[7]
Result
physiologic or elevated
total serum bilirubin
Test
Best test to confirm diagnosis. TSB should be measured if the TcB exceeds or is within 3 mg/dL of the phototherapy treatment threshold or if the TcB is ≥15 mg/dL. Collect blood and keep away from strong light sources; send for laboratory processing as soon as possible. If the rate of total serum bilirubin is ≥0.3 mg/dL per hour in the first 24 hours or ≥0.2 mg/dL per hour thereafter, the infant is at higher risk for subsequent hyperbilirubinemia.[7]
Result
increased
direct Coombs test
Test
To diagnose ABO or Rh isoimmunization.
Result
positive or negative
Tests to consider
hematocrit
Test
Capillary samples usually suffice. Needs central (venous or arterial) to confirm polycythemia.
Result
hemolytic anemia if <45%; polycythemia if >65%
CBC
Test
High or low WBC count can suggest sepsis. Thrombocytopenia can suggest sepsis.
Result
high or low WBC or platelet counts
reticulocyte count
Test
Increased counts are suggestive of hemolysis.
Result
normal or increased
peripheral blood smear
Test
Evidence of hemolysis. May aid in the diagnosis of hereditary spherocytosis.
Result
normal or abnormal red blood cell shapes/size
blood groups
Test
If mother is O and the neonate A or B, suggests ABO incompatibility. Rh-negative mother with Rh-positive neonate is suggestive of Rh incompatibility.
Result
ABO and Rh status
glucose-6-phosphate dehydrogenase (G6PD) screening
Test
Should be done after a couple of weeks to avoid false negative, because of higher enzyme levels in younger red blood cells in the circulation. If G6PD deficiency is strongly suspected but the measurement of G6PD activity is normal or close to normal, the G6PD activity should be measured at least 3 months later.[7]
Result
normal or decreased enzyme levels
osmotic fragility test
Test
Positive in hereditary spherocytosis.
Result
positive or negative
blood culture
Test
Positive in sepsis.
Result
positive or negative
liver function tests
Test
Decreased albumin levels may be helpful to evaluate bilirubin binding capacity and risk of bilirubin toxicity. An albumin concentration <3.0 g/dL is a hyperbilirubinemia neurotoxicity risk factor. Liver enzymes may be increased in congenital infections.
Result
normal, increased or decreased
urine for reducing substances
Test
Present in galactosemia, if neonate is receiving galactose-containing feeds.
Result
present or absent
plasma amino acids
Test
Abnormal in specific inborn errors of metabolism.
Result
normal or increased
urine organic acids
Test
Abnormal in specific inborn errors of metabolism.
Result
normal or increased
urine culture
Test
Positive in urinary tract infection.
Result
positive or negative
abdominal ultrasound
Test
Abnormal in specific cases of hepatocellular disease or obstructive causes of conjugated jaundice.[41]
Result
normal or abnormal
percutaneous liver biopsy
Test
Abnormal in paucity of intrahepatic bile ducts, metabolic and storage disorders, infection.[41]
Result
normal or abnormal
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