Related to the blood concentration in filter paper, which is not always constant.
4. Blood collection. Blood samples are collected for measurement of blood lipids and glucose. For lipid measurements, serum should be used in preference to plasma to avoid the diluting effect of anticoagulants, which results in about 3% difference in concentrations. Centrifuging. If samples for glucose measurements are taken, the samples should be centrifuged no later than 20-35 minutes after the sample is drawn. For serum samples, blood should be centrifuged within one hour after b The centrifuge should not be cold and blood specimens should be centrifuged at a temperature 15-24 C. For serum preparation blood should spin for 10 minutes at 1500 g. For plasma, the conditions are 15 minutes at 2000g to 3000g. Centrifuging. If samples for glucose measurements are taken, the samples should be centrifuged no later than 20-35 minutes after the sample is drawn. For serum samples, blood should be centrifuged within one hour after blood collection. Evacuated BCTs are generally cylindrical, measuring 50 mm to 150 mm in length and 10 mm to 20 mm in diameter (9). Most tubes for adult clinical specimens are 75 mm to 100 mm in length and 13 mm in diameter, and collect 2 to 10 mL of whole blood (9,10). To reduce the potential for splatter from the blood specimen when the rubber stoppers are removed from the collection tube, a stopper shield is used (e.g. Hemogard™). The stopper shield can be made from thermoplastic materials, such as polyethylene, polypropylene, and polyvinylchloride (8,26). Plasma angiotensinogen concentrations are typically in the first-order range of the renin enzymatic reaction, and the amount of Ang I produced by a constant amount of renin is linearly related to the angiotensinogen concentration (22)(26)(27). These precautions are especially important for plasma samples with a reduced renin/prorenin ratio, such as those from patients with primary aldosteronism, pregnancy, or diabetes (3)(8)(21)(22)(23) (Table 2 ⇑). Measurement of renin by activity assay or immunoassay requires special precautions to avoid unfolding and cleavage of the prorenin prosegment. Both cooling and low pH promote unfolding of the prorenin prosegment (15)(16)(17), whereas refolding of the prosegment is promoted at 37 °C and physiological pH (14)(17)(18)(19). These precautions are especially important for plasma samples with a reduced renin/prorenin ratio, such as those from patients with primary aldosteronism, pregnancy, or diabetes (3)(8)(21)(22)(23) (Table 2 ⇑). Measurement of plasma renin is important for the clinical assessment of hypertensive patients. Activity assays and immunoassays provide different, although complementary, information about plasma renin, which clinicians and clinical chemists need to understand if they are to correctly interpret these assays. These precautions are especially important for plasma samples with a reduced renin/prorenin ratio, such as those from patients with primary aldosteronism, pregnancy, or diabetes (3)(8)(21)(22)(23) (Table 2 ⇑). The information about collection date of the sample is critical and should be included. A precaution should be taken for the measurement of enzyme activity, related to the blood concentration in filter paper, which is not always constant. This concentration depends mainly on the sample's collection procedures [13] . Background. Mucopolysaccharidosis IVA (MPS IVA), or Morquio Syndrome type A, is an autosomal recessive disease caused by deficiency of the lysosomal enzyme N-acetylgalactosamine-6-sulfatase (GALNS), resulting in excessive lysosomal storage of keratan sulfate in many tissues and organs. Measurement of plasma renin is important for the clinical assessment of hypertensive patients. The most common methods for measuring plasma renin are the plasma renin activity (PRA) 1 assay and the renin immunoassay. These precautions are especially important for plasma samples with a reduced renin/prorenin ratio, such as those from patients with primary aldosteronism, pregnancy, or diabetes (3)(8)(21)(22)(23) (Table 2 ⇑). Enzyme activity = moles of substrate converted per unit time = rate × reaction volume. Enzyme activity is a measure of the quantity of active enzyme present and is thus dependent on conditions, which should be specified. The SI unit is the katal, 1 katal = 1 mol s −1, but this is an excessively large unit. The rate of a reaction is the concentration of substrate disappearing (or product produced) per unit time (mol L −1 s −1). The % purity is 100% × (specific activity of enzyme sample / specific activity of pure enzyme). Blood enzyme tests. Enzymes are chemicals which help to regulate a number of chemical reactions, and that take place in the body. Blood enzyme tests can be used to measure the levels and activity of certain enzymes. Some blood enzyme tests assess the liver enzymes and others test for damage to the heart
http://www.thl.fi/publications/ehrm/product2/part_iii4.htm http://www.thl.fi/publications/ehrm/product2/part_iii4.htm http://www.biochemia-medica.com/2014/24/31 http://www.clinchem.org/content/55/5/867.long http://www.clinchem.org/content/55/5/867.long http://www.clinchem.org/content/55/5/867.long http://www.sciencedirect.com/science/article/pii/S0009898111003135 http://www.clinchem.org/content/55/5/867.long https://en.wikipedia.org/wiki/Enzyme_assay http://www.medic8.com/blood-disorders/blood-test/types/blood-enzyme-tests.html
what precautions should be taken when collecting blood for assays of enzymatic activity