title: Hemoglobin to Hematocrit Ratio: The Strongest Predictor of Femoral Head Osteonecrosis in Children With Sickle Cell Disease.
abstract: BACKGROUND
  Femoral head osteonecrosis (ON) secondary to sickle cell disease (SCD) often progresses to femoral head collapse, requiring total hip arthroplasty. However, this treatment has a limited durability and patients with SCD have higher rates of complications, requiring multiple revision operations. Identifying risk factors linked to ON in SCD can facilitate earlier precollapse diagnosis and surgical treatment aimed at preservation of the native hip joint.
  
  
  METHODS
  Fifty-nine children treated at our institution between January 2001 and April 2012 with SCD and ON, as diagnosed by magnetic resonance imaging or radiographic imaging, were compared with age-matched and sickle cell phenotype-matched (SS, SC, Sβ, Sβ) controls with no evidence of ON. Two sided t-tests assuming unequal variances determined statistically risk factors and threshold values were assigned to calculate odds ratios.
  
  
  RESULTS
  Systolic blood pressure (P=1.2×10, OR=3.68), diastolic blood pressure (P=0.0084, OR=1.41), weight in the SCD-SS population (P=0.04, OR=1.85), and hemoglobin (Hb) in the SCD-SS population (P=0.036, OR=2.56) were elevated in cases. Curiously, dividing the Hb by the hematocrit to serve as a clinical proxy for the mean corpuscular Hb concentration (MCHC) produced an excellent predictor of ON (P=2.06×10, OR=5.17), which was especially pronounced in the SCD-SS subpopulation (P=2.28×10, OR=8.65). Among children with SCD, the overall prevalence of ON was 9% (59/658) and the phenotype with the highest prevalence of ON was Sβ thalassemia with an ON prevalence of 11.1%. There was no observed correlation between ON and height, body mass index, cholesterol, mean corpuscular volume, hematocrit, or glucocorticoid use.
  
  
  CONCLUSIONS
  These data support a novel clinical marker, the MCHC proxy, as the strongest predictor of ON in children with SCD. High-risk children should receive hip magnetic resonance imaging to diagnose early ON and facilitate interventions focused on hip preservation, forestalling, or possibly preventing, the need for total hip arthroplasty.
authors.affiliation: The Children's Hospital of Philadelphia, Philadelphia, PA.
authors.forename: Douglas
authors.initials: D
authors.lastname: Worrall
authors.forename: Kim
authors.initials: K
authors.lastname: Smith-Whitley
authors.forename: Lawrence
authors.initials: L
authors.lastname: Wells
mesh_terms: D000293:Adolescent; D000755:Anemia, Sickle Cell / Q000150:complications*; D001794:Blood Pressure; D016022:Case-Control Studies; D002648:Child; D002675:Child, Preschool; D005260:Female; D005271:Femur Head Necrosis / Q000209:etiology*; D006400:Hematocrit; D006454:Hemoglobins / Q000032:analysis*; D006801:Humans; D008297:Male; D010641:Phenotype; D012189:Retrospective Studies; D012307:Risk Factors
chemical_list: D006454:Hemoglobins