title: The test characteristics of head circumference measurements for pathology associated with head enlargement: a retrospective cohort study.
abstract: BACKGROUND
  The test characteristics of head circumference (HC) measurement percentile criteria for the identification of previously undetected pathology associated with head enlargement in primary care are unknown.
  
  
  METHODS
  Electronic patient records were reviewed to identify children age 3 days to 3 years with new diagnoses of intracranial expansive conditions (IEC) and metabolic and genetic conditions associated with macrocephaly (MGCM). We tested the following HC percentile threshold criteria: ever above the 95th, 97th, or 99.6th percentile and ever crossing 2, 4, or 6 increasing major percentile lines. The Centers for Disease Control and World Health Organization growth curves were used, as well as the primary care network (PCN) curves previously derived from this cohort.
  
  
  RESULTS
  Among 74,428 subjects, 85 (0.11%) had a new diagnosis of IEC (n = 56) or MGCM (n = 29), and between these 2 groups, 24 received intervention. The 99.6th percentile of the PCN curve was the only threshold with a PPV over 1% (PPV 1.8%); the sensitivity of this threshold was only 15%. Test characteristics for the 95th percentiles were: sensitivity (CDC: 46%; WHO: 55%; PCN: 40%), positive predictive value (PPV: CDC: 0.3%; WHO: 0.3%; PCN: 0.4%), and likelihood ratios positive (LR+: CDC: 2.8; WHO: 2.2; PCN: 3.9). Test characteristics for the 97th percentiles were: sensitivity (CDC: 40%; WHO: 48%; PCN: 34%), PPV (CDC: 0.4%; WHO: 0.3%; PCN: 0.6%), and LR+ (CDC: 3.6; WHO: 2.7; PCN: 5.6). Test characteristics for crossing 2 increasing major percentile lines were: sensitivity (CDC: 60%; WHO: 40%; PCN: 31%), PPV (CDC: 0.2%; WHO: 0.1%; PCN: 0.2%), and LR+ (CDC: 1.3; WHO: 1.1; PCN: 1.5).
  
  
  CONCLUSIONS
  Commonly used HC percentile thresholds had low sensitivity and low positive predictive value for diagnosing new pathology associated with head enlargement in children in a primary care network.
authors.affiliation: Department of Pediatrics and Child Health, The University of Manitoba, Winnipeg, Manitoba, Canada. cdaymont@mich.ca
authors.forename: Carrie
authors.initials: C
authors.lastname: Daymont
authors.forename: Moira
authors.initials: M
authors.lastname: Zabel
authors.forename: Chris
authors.initials: C
authors.lastname: Feudtner
authors.forename: David M
authors.initials: DM
authors.lastname: Rubin
mesh_terms: D049628:Body Size; D001927:Brain Diseases / Q000150:complications / Q000473:pathology*; D002675:Child, Preschool; D015331:Cohort Studies; D005260:Female; D030342:Genetic Diseases, Inborn / Q000150:complications / Q000473:pathology*; D057238:Growth Charts; D006257:Head / Q000473:pathology*; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D058627:Megalencephaly / Q000209:etiology* / Q000473:pathology; D008659:Metabolic Diseases / Q000150:complications / Q000473:pathology*; D011237:Predictive Value of Tests; D011320:Primary Health Care; D012189:Retrospective Studies; D012680:Sensitivity and Specificity