title: Relationship between haemoglobin and haematocrit in the definition of anaemia.
abstract: BACKGROUND
  Anaemia is the most frequent haematological disorder in childhood. The notion that defines naemia does not change throughout life, although parameters used for its evaluation show significant variations during childhood. Haematocrit (Hct) (%) is usually defined as three times the value of haemoglobin (Hgb) (g/dl), while the clinical definition of anaemia is related to either an abnormal Hct or Hgb value.
  
  
  OBJECTIVE
  To evaluate the agreement between Hgb and Hct values in the definition of anaemia, the relationship between these two parameters and their age-dependence.
  
  
  METHODS
  The Hct and Hgb paired values from children aged 2-18 months from Ifakara (Tanzania) and children aged 1-4 years from Manhiça (Mozambique) were analysed. Haematological determinations of the Manhiça samples were done using a KX-21N cell counter (Kobe, Japan) and Ifakara samples were analysed in a semiautomatic cell counter (Sysmex F800 microcell counter, TOA Medical Electronics, Kobe, Japan). The kappa-statistic was used to calculate the agreement between anaemia definitions in each group. Crude and multivariate relationship between Hct and Hgb levels were analysed by linear regression model estimation. The age-dependence of the crude ratio (Hct/Hgb) was analysed using linear regression models and fractional polynomials.
  
  
  RESULTS
  The prevalences of mild and moderate anaemia as defined by Hgb levels in the Manhiça group were 61% and 6%, respectively, and 41% and 2% by Hct. In the Ifakara group these were 74% and 10%, respectively, by Hgb and 42% and 3% by Hct, respectively. Agreement between mild and moderate anaemia definitions made up from Hgb or from Hct levels were from fair to moderate. Hct levels decreased with age for high Hgb levels, whereas they increased for low Hgb levels. The classification of cases is improved when higher age-related cut-off values for Hct are used. The crude relationship between Hct and Hgb levels was significantly different from 3, and this was modified by age. The evaluation of the age-dependence ratio (Hct/Hgb) showed a non-linear relationship with an asymptotic trend to 3.
  
  
  CONCLUSIONS
  Measurement of haematocrit count is easy and can be performed in most rural health care centres. However, the corresponding Hgb levels cannot be derived with an acceptable accuracy using the value 3 as a conversion factor. Furthermore, the commonly assumed 'equivalent' cut-off points for anaemia definitions need to be re-evaluated.
authors.affiliation: Centre de Salut Internacional, CSI, Hospital Clinic/IDIBAPS, Universitat de Barcelona, Barcelona, Spain. lquinto@clinic.ub.es
authors.forename: Llorenç
authors.initials: L
authors.lastname: Quintó
authors.forename: John J
authors.initials: JJ
authors.lastname: Aponte
authors.forename: Clara
authors.initials: C
authors.lastname: Menéndez
authors.forename: Jahit
authors.initials: J
authors.lastname: Sacarlal
authors.forename: Pedro
authors.initials: P
authors.lastname: Aide
authors.forename: Mateu
authors.initials: M
authors.lastname: Espasa
authors.forename: Inacio
authors.initials: I
authors.lastname: Mandomando
authors.forename: Caterina
authors.initials: C
authors.lastname: Guinovart
authors.forename: Eusebio
authors.initials: E
authors.lastname: Macete
authors.forename: Rosmarie
authors.initials: R
authors.lastname: Hirt
authors.forename: Honorathy
authors.initials: H
authors.lastname: Urassa
authors.forename: Margarita M
authors.initials: MM
authors.lastname: Navia
authors.forename: Ricardo
authors.initials: R
authors.lastname: Thompson
authors.forename: Pedro L
authors.initials: PL
authors.lastname: Alonso
mesh_terms: D017677:Age Distribution; D000740:Anemia / Q000097:blood / Q000453:epidemiology / Q000503:physiopathology*; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D005260:Female; D006400:Hematocrit; D006454:Hemoglobins / Q000032:analysis*; D006801:Humans; D007223:Infant; D008297:Male; D015233:Models, Statistical; D009073:Mozambique / Q000453:epidemiology; D011159:Population Surveillance / Q000379:methods; D015995:Prevalence; D013636:Tanzania / Q000453:epidemiology
chemical_list: D006454:Hemoglobins