tailieunhanh - PDQ BIOCHEMISTRY - PART 4

Nếu nhạy cảm cho một enzyme chẩn đoán là 90%, có nghĩa rằng 10% những người thử nghiệm sẽ được coi là không có bệnh, trong khi, trên thực tế, những 10% là âm tính giả, bị mất bởi các mức tiêu chuẩn quy định. Tương tự như vậy, đặc trưng cho một enzyme chẩn đoán cụ thể được định nghĩa là Đúng | 100 PDQ BIOCHEMISTRY If the sensitivity for a diagnostic enzyme is 90 it means that 10 of those tested would be considered not to have the disease while in fact these 10 are false negatives missed by the standard levels set. Similarly specificity for a particular diagnostic enzyme is defined as True negatives All those without the disease X 100. If the specificity for the enzyme is 90 there would be 10 who would be considered to have the disease but who are in fact disease-free . these are false positives . Other considerations for the usefulness of diagnostic enzymes are the time it takes for a serum enzyme to appear during or following a pathologic state. An enzyme that appears early in the course of a disease would obviously allow you to make a therapeutic intervention that much earlier in an effort to arrest or ameliorate the condition. Another factor is the use of isoenzymes as we discussed earlier for creatine kinase and LDH that would indicate the involvement of a specific tissue and make diagnosis that much more accurate. Thus prior to introducing a new enzyme diagnostic test it should meet the following criteria. The enzyme should be stable so that a refrigerated sample may still show the enzyme activity. Usually samples for assay are not frozen. The enzyme should be easily and cheaply assayed. It should have reasonably high activity so that it can be detected at relatively low levels. It should have a degree of tissue specificity directing you to a likely pathology in a particular tissue. The level of the enzyme in serum should also reflect the severity of the pathology. One other consideration is the source of the enzyme. Usually plasma or serum samples derived from blood are used in diagnosis. It may also be possible to assess blood cells for enzyme levels for example red and white blood cells or platelets. Urine may be used for enzyme determination particularly in renal and urinary tract diseases as may other fluids such as amniotic fluid or gastric

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