title: A multicentre analysis of four low-density lipoprotein cholesterol direct assays in samples with extreme high-density lipoprotein cholesterol concentrations.
abstract: BACKGROUND
  Although LDL-C has been traditionally estimated using the Friedewald formula (FF), several direct homogeneous assays have been developed to overcome the limitations of this formula and the complicated manual procedure required in the reference method. However, several differences have been reported between these assays in certain situations.
  
  
  METHODS
  Two groups of 105 samples with extreme low and high HDL-C concentrations were processed, employing four different instruments and with the reagents for total cholesterol, triglycerides, HDL-C and LDL-C provided by the distinct manufacturers.
  
  
  RESULTS
  Statistical tests indicated important differences between HDL-C and LDL-C homogeneous methods. Poor correlation, significant bias and high discrepancy in cardiovascular disease risk classification were observed for LDL-C direct assays in the low HDL-C group, whereas better results were obtained when comparing LDL-C levels estimated with the FF. In contrast, three of the four instruments generated LDL-C direct results with a good agreement in the high HDL-C group, even though an appreciable misclassification percentage in risk categories must be taken into account.
  
  
  CONCLUSIONS
  Our results indicate that extreme low or high HDL-C levels can represent a non-previously described source of variation between commercially available LDL-C homogeneous assays.
authors.affiliation: Laboratory of Clinical Chemistry, Hospital Virgen de la Salud, Complejo Hospitalario de Toledo, Spain. Electronic address: jesust@sescam.jccm.es.
authors.forename: Jesús
authors.initials: J
authors.lastname: Timón-Zapata
authors.affiliation: Laboratory of Clinical Chemistry, Hospital Virgen de la Salud, Complejo Hospitalario de Toledo, Spain. Electronic address: ejlaserna@sescam.jccm.es.
authors.forename: Emilio José
authors.initials: EJ
authors.lastname: Laserna-Mendieta
authors.affiliation: Laboratory of Clinical Chemistry, Hospital General Universitario de Ciudad Real, Spain. Electronic address: lsaenz@sescam.jccm.es.
authors.forename: Luis Francisco
authors.initials: LF
authors.lastname: Sáenz-Mateos
authors.affiliation: Laboratory of Clinical Chemistry, Hospital Universitario de Guadalajara, Spain. Electronic address: luchyruiz44@hotmail.com.
authors.forename: Lucía
authors.initials: L
authors.lastname: Ruiz-Trujillo
authors.affiliation: Laboratory of Clinical Chemistry, Hospital Universitario de Fuenlabrada, Madrid, Spain. Electronic address: ana.arpa@salud.madrid.org.
authors.forename: Ana
authors.initials: A
authors.lastname: Arpa-Fernández
authors.affiliation: Laboratory of Clinical Chemistry, Hospital General Universitario de Ciudad Real, Spain. Electronic address: tjavierpm@sescam.jccm.es.
authors.forename: Teodoro Javier
authors.initials: TJ
authors.lastname: Palomino-Muñoz
authors.affiliation: Laboratory of Clinical Chemistry, Hospital Universitario de Guadalajara, Spain. Electronic address: pilarloechesjimenez@hotmail.com.
authors.forename: María Pilar
authors.initials: MP
authors.lastname: Loeches-Jiménez
authors.affiliation: Laboratory of Clinical Chemistry, Hospital Virgen de la Salud, Complejo Hospitalario de Toledo, Spain. Electronic address: magosere@yahoo.es.
authors.forename: Manuel
authors.initials: M
authors.lastname: Gómez-Serranillos
mesh_terms: D008076:Cholesterol, HDL / Q000097:blood*; D008078:Cholesterol, LDL / Q000097:blood*; D006801:Humans; D015233:Models, Statistical
chemical_list: D008076:Cholesterol, HDL; D008078:Cholesterol, LDL
keywords: Direct homogeneous assays; Friedewald formula; High-density lipoprotein cholesterol; Low-density lipoprotein cholesterol