title: Difference between true functional haemoglobin and pre-dialysis haemoglobin is associated with plasma volume variation: a multicentre study.
abstract: OBJECTIVE
  Due to the well-known intradialytic haemoglobin (Hb) change, it has been suggested that true functional Hb differs from pre-dialysis Hb. However, mechanisms of this change are not understood properly. We aimed at studying the role of plasma volume variation.
  
  
  METHODS
  This is a multicentre study with two consecutive phases. First, true functional Hb was predicted by Krisper's formula that estimates time-averaged haemoglobin concentration (TAC-Hb) and by the average (Avg-Hb) of Pre-Hb and Post-Hb (n = 346). Erythropoiesis-stimulating agent (ESA) doses were estimated according to the FDA instructions. Second, we investigated the correlations between Hb changes (ΔHb), body weight loss (ΔBW) and relative plasma volume changes (%ΔPV) in subjects with a weight gain higher than 1 kg (n = 208).
  
  
  RESULTS
  First: Avg-Hb and TAC-Hb were similar to each other and higher than midweek Pre-Hb (p < 0. 002). Odds of having an Hb change >1 g/dL were 0.415. Odds were similar in both women and men [odds ratio (OR) 0.923; 95 % confidence interval (CI) 0.591-1.441]. If ESA doses were estimated by TAC-Hb or Avg-Hb instead of Pre-Hb, they should be lower in 40 % of the 346 patients. Second: Mean %ΔPV was -12.1 % (95 % CI -10.72/-13.48), and mean ΔHb was 1.1 g/dL (95 % CI 0.97/1.25). Correlation between ΔHb and %ΔPV was -0.92 (r (2) 0.84) whereas that of ΔHb/ΔBW was just -0.45 (r (2) 0.21; p < 0.000). Prevalence of ΔHb >1 g/dL was independent of ΔBW from 1.4 to 6.3 kg. By contrast, prevalence of ΔHb >1 g/dL in %ΔPV quartiles was clearly linear: 0, 52, 90 and 100 %, respectively.
  
  
  CONCLUSIONS
  Plasma volume variations play a major role in intradialytic Hb change. True functional Hb should be estimated in all patients with a weight gain higher than 1 kg.
authors.affiliation: Dialisis Madariaga, Avenida Buenos Aires y Calle 21, 7163, General Madariaga, Provincia de Buenos Aires, Argentina, siga@telpin.com.ar.
authors.forename: Esteban
authors.initials: E
authors.lastname: Siga
authors.forename: Miguel
authors.initials: M
authors.lastname: Fernandez
authors.forename: Mario
authors.initials: M
authors.lastname: Galarza
authors.forename: Vito
authors.initials: V
authors.lastname: Mesina
authors.forename: Hugo
authors.initials: H
authors.lastname: De Palma
authors.forename: Raul
authors.initials: R
authors.lastname: Coste
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006397:Hematinics / Q000627:therapeutic use; D006454:Hemoglobins / Q000032:analysis*; D006801:Humans; D007674:Kidney Diseases / Q000628:therapy*; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D010953:Plasma Volume; D011237:Predictive Value of Tests; D006435:Renal Dialysis; D015430:Weight Gain
chemical_list: D006397:Hematinics; D006454:Hemoglobins