PREVALENCE AND GENOTYPE OF weakD RED BLOOD CELL PHENOTYPES IN SWISS BLOOD DONORS


Adriana Méndez, Pascale Jaquet, Karin Hardegger, Annette Schille, Monika Furrer and Beat M. Frey Stiftung Zürcher Blutspendedienst SRK, CH-8001 Zürich (www.zhbsd.ch)

BACKGROUND: 
Rarely, Rh positive individuals (RH1+) are misdiagnosed as Rh negative (RH1-) by routine serology due to quantitative and/or qualitative aberrant expression of Rhesus D (DP donors). There are two different mechanisms underlying DP phenotypes: First, red blood cells (RBC) showing reduced quantity of RH1 epitopes (weakD (wD)) due to point mutations of intramembranous part of Rh protein (Rhp). Alternatively, RBCs carrying aberrant extramembranous Rhp with loss of RhD epitopes (partialD (pD)). Blood products (BP) from DP donors may be mislabelled as Rh negative (RH1-) and potentially will induce anti-D antibodies in RH1- recipients or may lead to haemolytic transfusion reactions due to Rh incompatibility upon transfusion. Prevalence, phenotypes and genotypes of aberrant Rhp expression in Swiss blood donors (BD) have been studied.

METHODS:
Routine Rh phenotyping (RRP): Hemagglutination testing using two different monoclonal anti-D antisera (Biotest) in microtiter plates. RH1- samples by RRP: Confirmation by tube testing using anti-D monoclonal IgG+IgM (Immucor) and by gel sedimentation testing using polyclonal anti-D antiserum (DiaMed). Aberrant RH1 phenotypes: Examination of wD genotype by commercial wD genotyping kit (InnoTrain). Examination of pD by serological and molecular methods. RH1 expression: Quantification by flowcytometry relative to R1R1 cells 1.

RESULTS:
From 1.1.2003 to 31.12.2004 7571 newly registered BDs were screened for Rh phenotype. 6300 BDs (83.2%) were RH1+, 1271 (16.8%) BDs were RH1-. 12/1271 (1.0%) of RH1- BDs by RRP were found aberrant RH1+, giving a prevalence of DP donors of 0.2%. 54 DP donors of our donor registry were available for thorough reanalysis: 52/54 (96%) were diagnosed wD genotypes (Table) and 2/54 (4%) were partialDVI. RH1 expression of wD cells varies from 0.3% to 20% relative to R1R1 cells. There is no linkage of wD Type and RH1 expression.

CONCLUSIONS:

  • Aberrant RH1 expression in blood donors most likely is due to wD genotype (>95%).
  • 87% of wD genotypes belong to wD type 1–3 which is consistent with other studies of Caucasian populations.
  • 1% of Rh negative BDs express low level RH1.
  • wD phenotypes exhibit sufficient RH1 expression to induce anti-D antibodies in RH1- recipients. Therefore, searching for low level RH1 expression by RH1- BDs and the correct labelling of the respective blood products (= Rh positive) are important.
Table: Prevalence of WeakD types in DP Swiss Blood Donors
Weak D-Typ
(SSP)
 

RH1 low expressing donors
N = 52 (%)

Type 1
32 (62%)
Type 2
11 ( 22%)
Type 3
3 (6%)
Other Weak D
3 (6%)
Type 1+2
1 (2%)
Type 5
1 (2%)