December 2010 Clinical Laboratory News: Diagnostic Profiles

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Pooled NAAT Testing Not Cost-Effective in Most Settings

New research indicates that pooled nucleic acid amplification testing (NAAT) screening for acute HIV infection (AHI) after negative third-generation or rapid tests is not cost-effective for most settings (PLOS Medicine 2010;7:e10000342). This strategy appears to be cost-effective only when targeted to settings with very high HIV incidence or where cost-effectiveness is not a major concern.

The analysis considered the potential benefits of pooled NAAT, such as identifying and notifying individuals with AHI and cases averted as a result of NAAT, compared with repeat antibody testing at different intervals. The investigators conducted the study concurrent with the Centers for Disease Control and Prevention’s multisite study that used pooled NAAT screening for AHI detection in different clinical settings, including HIV testing and counseling sites, municipal sexually transmitted disease clinics, and a community clinic serving men who have sex with men.

The researchers used a mathematical model of HIV transmission and conducted a micro-cost study of pooled NAAT by completing time-motion studies in a lab that performed NAAT and by calculating in detail costs associated with NAAT such as reagents, equipment, consumables, and the like. They found that pooled NAAT after a negative third-generation immunoassay had cost-effectiveness ratios of $370,000–$1 million per quality adjusted life year in counseling and testing sites and at STD clinics, far exceeding acceptable ranges of cost-effectiveness thresholds.

The authors conclude that pooled NAAT screening for AHI should be reserved for settings that serve the highest-incidence populations or for circumstances, such as blood donor screening, where cost-effectiveness is not a primary consideration.

Study Decries Use of One CRP Threshold for Statin Therapy

An analysis by British researchers suggests that a single C-Reactive protein (CRP) threshold value for cardiovascular risk prediction could lead to inequalities in eligibility for statin treatment that may not accurately reflect underlying levels of cardiovascular risk (Circ Cardiovasc Genet 2010;3:436–44). “A one size-fits-all threshold value … could diminish the opportunity to receive a statin in individuals from certain ethnic backgrounds while increasing this opportunity among others,” the authors wrote.

The researchers conducted the investigation in light of recent developments surrounding the use of a CRP value >2 mg/L as a threshold for rosuvastatin therapy. The landmark Justification for the Use of Statins in Primary Prevention: an Intervention Trial Evaluating Rosuvastatin (JUPITER) study evaluated the efficacy of statins in subjects considered at risk because of CRP values >2 mg/L. Subsequently, and at least partially on the basis of the JUPITER findings, the Food and Drug Administration licensed rosuvastatin for primary prevention of cardiovascular disease in patients with CRP >2 mg/L along with other risk factors. While numerous studies have linked CRP levels with development of cardiovascular disease, most of the participants have been of European ancestry and there is limited data about CRP variations in different ethnic populations.

To examine the latter issue, the researchers conducted a systematic review of studies in healthy populations that reported CRP concentrations for any ethnic group. They also investigated genetic and nongenetic determinants of inter-ethnic CRP differences using human HapMap and SeattleSNP databases, and conducted a participant level analysis as part of the Wandsworth Heart and Stroke Study (WHSS).

The systematic analysis revealed “substantial differences” in CRP concentrations across various ancestry groups, with geometric mean CRP values for black, Hispanic, and South Asian subjects of 2.6, 2.51, and 2.34 mg/L, respectively, compared with 2.03 and 1.01 mg/L in Caucasians and East Asians, respectively. These differences, which were not explained by study design or CRP assay, remained after adjustment for age and body mass index. The researchers also found that HapMap frequencies of CRP polymorphisms known to associate with CRP concentration but not coronary heart disease events differed by ancestry. Finally, WHSS results indicated that body mass index, systolic blood pressure, and smoking contributed to between-group differences, but the majority of CRP variance was unexplained.

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