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smear showing the characteristic bite cells. During hemolysis, G6-PD levels are usually normal because the susceptible red cells are destroyed; testing must consequently be delayed until about 30 days after discontinuation of the offending agent. Some laboratories report results as units/g Hgb, with fewer than three indicating severe deficiency, in men and homozygous women; other labs report qualitative results.

HLA-B*5701: It appears that nearly all true abacavir (ABC) hypersensitivity reactions (HSR) have a genetic basis attributed to carriage of the MHC class I allele HLA-B*5701 (Proc Nat Acad Sci USA 2004; 101:4180; AIDS 2005; 19:979). Clinical studies in Western Australia (CID 2006; 43:99) the UK (Antiviral Ther 2006;11:L11) and France (JAIDS 2007; 45:1) support the strong correlation. The large definitive trial was "PREDICT" in which study was PREDICT, a prospective double- blind trial in which 1660patients with intended ABC use were tested and randomized for prescribing physicians to know or not know results of HLA-B*5701 screening test (NEJM 2008;358:568). ABC HSR was confirmed with a blinded independent skin patch test that is not commercially available. The sensitivity of HLA B*5701 testing was 43% in patients with clinically suspected ABC HSR and 100% sensitivity for immunologically confirmed reactions. Specificity was 97% and 98% respectively (Table 2-19). The conclusion was that a negative test for HLA-B*5701 had a 100% negative predictive value, meaning a negative test excluded this complication within the limits imposed by the sample size. Unconfirmed rare exceptions have been reported (AIDS 2007;21:2533). HLA-B*5701 testing is now recommended in any patient in whom first use of ABC is being considered. 

HEALTH SCREENS

  • Prostrate specific antigen (PSA): African-American men >45 years; other men >50 years
  • Colonoscopy: All patients >50 years
  • Mammography: All women >50 years
  • Bone density: Patients with risk factors for osteoporosis

 

TABLE 2-19:

Results of PREDICT in 1,660 patients (NEJM 2008;358:568).
  Clinically suspected HSR Immunologically confirmed HSR*
  Pos Neg Pos Neg
HSR 30 36 23 0
No HSR 19 792 25 794
PPV* 62% - 46% -
NPV* - 96% - 100%

*HSR = hypersensitivity reaction; PPV = Positive predictive value; NPV = negative predictive value

**Prevalence of HLA-B* 5701 is highly variable by race: US Caucasians 8%, US Asians 1%, US African-Americans 2%, US Hispanics 2%, UK 8%, Western Europe -7%, China and Japan <1% S. American Caucasians 5-7%, Australians 8%, Sub-Saharan Africa <1%, Mediterranean 1-2%, India 5-20% (HIV Ther 2003; 8:36)

This test is commercially available, results are positive or negative, the time to report is 1- 2 weeks and the cost is from commercial labs is usually $90-$125.
2007 © John G. Bartlett, M.D. All rights reserved.58

Chapter 2: Laboratory Tests

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