Serum enzyme diagnosis

Assay of plasma enzymes aids diagnosis and prognosis. For example, a myocardial infarction elevates serum levels of lactate dehydrogenase isozyme I,. 

Table 7-2. Principal serum enzymes used in clinical diagnosis. Many of the enzymes are not specific for the disease listed.

Along with an effective electrolyte and screening program for genetic disease, the laboratory of Neonatology needs to have the capability of analyzing for other components in blood serum, which aid in the diagnosis of disease. These include such determinations as alkaline phosphatase, and various other enzymes, creatinine, uric acid and a host of other components which are normally assayed by the main clinical laboratory. 

Many enzyme activities have been proposed for diagnosis, in serum, urine, cerebrospinal fluid and other body fluids, and the proposed methods have been reviewed elsewhere (17). Here we will confine ourselves to the tried and most commonly used enzyme activities which yield useful information in ambulatory or hospital patients. 

Amylase enters the blood largely via the lymphatics. An increase in hydrostatic pressure in the pancreatic ducts leads to a fairly prompt rise in the amylase concentration of the blood. Neither an increase in volume flow of pancreatic juice nor stimulation of pancreatic enzyme production will cause an increase in senm enzyme concentration. Elevation of intraductal pressure is the important determinant. Stimulation of flow in the face of obstruction can, however, augment the entry of amylase into the blood, as can disruption of acinar cells and ducts. A functional pancreas must be present for the serum amylase to rise. Serum amylase determination is indicated in acute pancreatitis in patients with acute abdominal pain where the clinical findings are not typical of other diseases such as appendicitis, cholecystitis, peptic ulcer, vascular disease or intestinal obstruction. In acute pancreatitis, the serum amylase starts to rise within a few hours simultaneously with the onset of symptoms and remains elevated for 2 to 3 days after which it returns to normal. The peak level is reached within 24 hours. Absence of increase in serum amylase in first 24 hours after the onset of symptoms is evidence against a diagnosis of acute pancreatitis (76). 

The diagnosis of HCV infection is confirmed with a reactive enzyme immunoassay for anti-HCV. Serum transaminase values are elevated within 4 to 12 weeks after exposure. 

Diagnosis If signs and symptoms spelled out above are noted in large numbers of geographically clustered patients, exposure to aerosolized ricin is the suggested cause. The rapid time course of severe symptoms and death would be unusual for infectious agents. Laboratory findings are nonspecific except for specific serum ELISA (enzyme-linked immunosorbent assay). Acute and convalescent sera (plural of serum ) should be collected. 

Probably the most effective use of XRF and TXRF continues to be in the analysis of samples of biological origin. For instance, TXRF has been used without a significant amount of sample preparation to determine the metal cofactors in enzyme complexes [86]. The protein content in a number of enzymes has been deduced through a TXRF of the sulfur content of the component methionine and cysteine [87]. It was found that for enzymes with low molecular weights and minor amounts of buffer components that a reliable determination of sulfur was possible. In other works, TXRF was used to determine trace elements in serum and homogenized brain samples [88], selenium and other trace elements in serum and urine [89], lead in whole human blood [90], and the Zn/Cu ratio in serum as a means to aid cancer diagnosis [91]. 

Transaminases are also found in other tissues, from which they leak from the cells into the blood when injury occurs. Measurement of serum enzyme activity (serum enzyme diagnosis see also p. 98) is an important method of recognizing and monitoring the course of such injuries. Transaminase activity in the blood is for instance important for diagnosing liver disease (e.g., hepatitis) and myocardial disease (cardiac infarction). 

All of the above-mentioned patterns are specific for the particular disease. The method is suitable as an initial screen to identify those patients in whom such a disorder must be excluded. The diagnosis must then be confirmed by enzyme analysis in serum, leucocytes or cultured skin fibroblasts or by way of mutation analysis. 

Fig. 4.5.2 Actual strategies for CDG diagnosis. Initial investigations on CDG patients are routinely carried out by isoelectric focusing (IEF) of serum transferrin. With a CDG type I pattern, subsequent analysis should imply determination of phosphomannomutase (PMM) and phos-phomannose isomerase (PMI) activities. Further studies, like analysis of the lipid-linked- and protein-bound-oligosaccharides, determination of enzyme or sugar transporter activities and molecular biology studies often have to be performed in more specialised laboratories. HPLC High-performance liquid chromatography, TLC thin-layer chromatography...

In a retrospective review of 497 patients taking propylthiouracil for hyperthyroidism, clinically overt hepatitis developed in six patients at 12-49 days after starting the drug (50). Jaundice and itching were present in five, fever in two, rash in two, and arthralgia in one. Serum bilirubin, alanine transaminase, and alkaline phosphatase were increased in five, four, and six patients respectively. The type of hepatic injury was cholestatic in three, hepatocellular in one, and mixed in two. There were no differences in age, sex, drug dose, or serum thyroid hormone concentrations at time of diagnosis in those with hepatic injury compared with those without. Liver function normalized in all patients at 16-145 days after withdrawal of propylthiouracil. In addition to these cases of overt liver injury, 14% of the cohort had mild asymptomatic liver enzyme rises at a mean of 75 days after the start of treatment. 

In recent years, the importance of enzyme levels in body fluids for clinical diagnosis has been recognized. It has been established that activities of secreted enzymes and cellular enzymes in serum are a sensitive indication of the pathophysiological condition of the body. Specific and sensitive substrates play a prominent role for this purpose. Fluorogenic substrates, e.g., enable sensitive micro-analyses. 

Biochemically, I-cell disease is characterized by excessive secretion of newly synthesized lysosomal enzymes into body fluids and concomitant loss of respective intracellular activities in fibroblasts. Shown in Table 17-1 are representative lysosomal enzyme activity levels in serum from patients with I-cell disease and those with the closely related disorder pseudo-Hurler poly dystrophy, indicating significantly increased levels of lysosomal enzyme activity. Germane to the biochemical diagnosis is the characteristic pattern of lysosomal enzyme deficiency in cultured fibroblasts, that is, an increase in the ratio of extracellular to intracellular enzyme activity (Table 17-2). It is interesting to note that not all lysosomal (i.e. intracellular)... 

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