We think about hereditary spherocytosis (HS) a lot in the newborn nursery - whenever we review the differential diagnosis for neonatal jaundice, it is mentioned. And if we know that there is a family history of HS, we are maybe a little more aggressive in treating hyperbilirubinemia, as there is a higher risk for hemolytic disease.
However, for multiple reasons, it’s hard to diagnose HS in the newborn. In 2015, Christensen et al published an article that described the Neonatal HS Index, which is calculated by dividing the mean corpuscular hemoglobin concentration (MCHC) by the mean corpuscular volume (MCV). They reported a sensitivity and specificity of >95% of identifying HS if the HS Index is >0.36. However, they tested the HS Index in a largely white population, so it’s unclear how helpful this measure is for other populations.
This week in Pediatrics(10.1542/peds.2020-021642), we are early releasing an article by a group at Kaiser Permanente, led by Dr. Nicole Weiss, which describes the results of a study in which they assessed the utility of the HS Index in a racially and ethnically diverse population and among babies with and without hyperbilirubinemia.
They used a retrospective cohort of 670,000 infants born in the Kaiser Permanente network between 1995 and 2015. 79 infants were eventually diagnosed with HS. They found that, using the cut point of 0.36, the HS Index was 56% sensitive and 93% specific. They also found that it had better reliability when the infant’s total serum bilirubin was <10 mg/dL.
We asked Dr. Patrick Gallagher from Yale University to provide a commentary on this study (10.1542/peds.2021-051100). He felt that the HS Index should not be used as a definitive diagnostic tool but could be considered an adjunctive tool, similar to how we use the Mentzer index (MCV/RBC) to discriminate between iron-deficiency anemia and thalassemia trait.
Check out the article and commentary. Reading the details will help you figure out if using the HS Index will be helpful to use with your patient population.
