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4 Cards in this Set
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What is PHI?
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This is prostate health index (PHI) and is a blood test that combines %fPSA as well as a subcategory of PSA known as pro-PSA.
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What is free PSA?
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The majority of PSA is bound in the bloodstream to carrier proteins but a small amount 5-35% is unbound in the serum. Although prostate cancer cells do not produce more PSA than benign prostate epithelium, the PSA produced from malignant cells appears to escape proteolytic processing. Thus men with prostate cancer have a greater fraction of serum PSA complexed to ACT and a lower percentage of total PSA that is free compared with men without prostate cancer.
Free PSA - think patient is free from cancer if have more free PSA. |
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When is %fPSA FDA approved for at what PSA interval?
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he role for %fPSA is more applicable to PSA levels less than 10 ng/mL, because the positive predictive rate of total PSA above 10 to 20 ng/mL has been demonstrated to be as high as 80%. Currently, %fPSA is approved by the Food and Drug Administration (FDA) for use to aid PSA testing in men with benign DRE and minimal PSA elevations, within the diagnostic gray zone of 4 to 10 ng/mL. If PSA levels are less than 4.0 ng/mL, more recent data have demonstrated the utility of %fPSA when deciding whether a patient requires an initial or repeat biopsy.
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What is proPSA? What is pPSA?
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Classification of free PSA isoforms can be done by assessing the presence or absence of internal cleavages, in which case the respective “forms” are termed “nicked” or “intact.” PSA originates with a 17–amino acid chain that is cleaved to yield a precursor inactive form of PSA termed proPSA (pPSA) (Zhang et al, 1995; Kumar et al, 1997, 2000; Mikolajczyk et al, 1997, 2001, 2002; Peter et al, 2001). As depicted in Figure 98–6, the precursor form of PSA contains a 7–amino acid proleader peptide, in addition to the 237 constituent amino acids of mature PSA, and is termed [–7]pPSA. Once released, the proleader amino acid chain is cleaved at the amino terminus by hK2, converting pPSA to its active 33-kD PSA form. In addition to hK2, pPSA may be activated to PSA by other prostate kallikreins, including hK4 (Takayama et al, 1997). Incomplete removal of the 7–amino acid leader chain has led to the identification of various other truncated or clipped forms of pPSA. These include pPSAs with 2, 4, and 5 leader amino acids ([–2]pPSA, [–4]pPSA, and [–5]pPSA) (Zhang et al, 1995; Kumar et al, 1997, 2000; Mikolajczyk et al, 1997, 2001, 2002; Peter et al, 2001). With cellular disruption, these inactive forms circulate as free PSA and may constitute the majority of the circulating free PSA in patients with CaP
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