Paroxysmal nocturnal haemoglobinuria testing in blood transfusion laboratories: do they go with the flow?

Paroxysmal nocturnal haemoglobinuria (PNH) is a rare stem cell disorder causing, in untreated patients, symptoms that include renal damage, thrombosis and increased mortality. When correctly diagnosed and treated, patients have reduced symptoms and normal life expectancies. Historically PNH testing resided within blood transfusion laboratories using techniques that were insensitive, for example, the Ham test. However, technology has evolved and flow cytometry is now regarded as the gold standard methodology. Given the clinical importance of diagnosing PNH correctly, we undertook a study to examine PNH testing procedures in blood transfusion laboratories within the UK and Ireland to determine implementation of best practices. An online survey was issued to 386 blood transfusion laboratories in the UK and Ireland requesting details of their current PNH testing practices and procedures. There were 143 responses, representing a 37% response rate. Of these, we identified seven laboratories undertaking PNH testing using obsolete methodologies. Furthermore, multiple centres did not refer samples for confirmatory testing by national PNH reference centres and inclusion on the national PNH disease registry. Staff handling requests for PNH testing should ensure that all samples are tested in accordance with current best practices using only flow cytometry.

A WHO reference reagent to standardize haemagglutination testing for anti-A and anti-B in serum and plasma: international collaborative study to evaluate a candidate preparation.

BACKGROUND AND OBJECTIVES: The aim of the study was to evaluate a lyophilized serum preparation, 14/300, for its suitability to serve as a World Health Organization (WHO) Reference Reagent to standardize and control haemagglutination titrations for anti-A and anti-B in serum and plasma, in an international collaborative study. MATERIALS AND METHODS: Serum preparation 14/300 and two plasma-based reserve preparations, 14/304 (high titre anti-A) and 14/208 (high titre anti-B), were titrated by 24 laboratories in 13 countries using direct (DRT) and indirect (IAT) haemagglutination techniques. RESULTS: There was eightfold to 64-fold variation in reported titres per preparation and method across laboratories, that is, titres extended over 4-7 dilutions, although intralaboratory variability was generally good, with over 90% of replicate titres within a twofold range. There was a reduction in interlaboratory variability when titres of the reserve preparations were adjusted relative to those of the candidate Reference Reagent. CONCLUSION: The establishment of 14/300 as a WHO Reference Reagent for high titre anti-A and anti-B in serum, with nominal anti-A and anti-B titres of 128 for DRT, and nominal anti-A and anti-B titres of 256 for IAT, will facilitate global standardization of haemagglutination titrations for anti-A and anti-B in patient samples and blood components.

The United Kingdom National External Quality Assessment Scheme (blood transfusion laboratory practice): trends in proficiency and practice between 1985 and 2000.

Proficiency in blood transfusion laboratory practice has improved over the last 15 years (1985-2000). Error rates for ABO grouping have fallen from 0 x 19 to 0 x 02% (P = 0 x 003). A similar trend is evident for antibody screening, with error rates for false negative antibody screens falling from 3 x 2 to 0 x 5% (P < 0 x 001), and for antibody identification, for sera containing a single alloantibody, with error rates falling from 8 x 8% to 0 x 9% over the last 10 years (P < 0 x 001). Proficiency in serological crossmatching to detect clinically significant non-ABO incompatibilities (other than Kidd), has also improved (P < 0 x 001). However, error rates for RhD grouping have not changed and there has been a recent decline in proficiency in detecting weak ABO incompatibilities and Kidd antibodies with heterozygous cells. Procedures for pretransfusion testing have also been rationalized over this time. The indirect antiglobulin test (IAT) is used in isolation by 73% of laboratories for antibody screening, and 10% rely on the direct room temperature (DRT), immediate spin (IS) crossmatch in the absence (current and/or historical) of clinically significant antibodies. Despite the improvements in error rates that have occurred alongside the rationalizations, there is still evidence of noncompliance with current published BCSH guidelines and manufacturers' instructions.

The computer crossmatch: a safe alternative to the serological crossmatch.

The crossmatch has evolved from including a wide range of techniques through a test purely to eliminate ABO incompatibility (immediate spin) to computer crossmatching in which no serological testing is carried out and validation ensures the correct ABO/RhD type blood is issued. The crossmatch was always considered to be the most important feature of the compatibility test and in particular the antiglobulin phase; however, there are potential risks associated with serological and computer crossmatching including technical and procedural errors. The use of immediate spin and computer crossmatch change the emphasis for safety of the compatibility test from the crossmatch to the antibody screen. UK guidelines have now been published describing the features necessary for the introduction of computer crossmatching. Computer crossmatching is used by many institutions in various countries. It is considered safe practice and brings benefits to the laboratory and the patient. Compatibility testing is only one element of the blood transfusion procedure; the others are equally as important and include correct patient identification at the time of collection of the blood sample and at the administration of the blood transfusion.