Clinical Chemistry MCQ

Of the three methods to measure glucose, glucose oxidase, hexokinase, and glucose dehydrogenase, the hexokinase method is considered virtually specific for glucose.

The classic Jaffe reaction involves complexing of creatinine with an alkaline picrate solution to produce a red complex (Janovski complex).

Triglycerides are most adversely affected by recent food intake, and therefore a fast is always recommended for triglyceride analysis.

In healthy individuals when the kidneys and lungs are functioning at full capacity the ratio of bicarbonate to carbonic acid is 20:1.

A tungsten-filament lamp is the most common light source for photometry in the visible region. It provides a continuous spectrum (360-800 nm) from the near infrared (IR) through the visible to the near ultraviolet (UV) region. Most of the radiant energy is in the near IR. Only about 15% is in the visible region—the region usually used. Because of the large emission in the near IR, tungsten lamps generate a significant amount of heat. Hydrogen and deuterium lamps are used for work in the 200-375 nm range. The mercury vapor lamp does not provide a continuous spectrum, emitting radiation at specific wavelengths.

The kidney is responsible for acid-base balance through the removal of H ions via (1) the reaction of the hydrogen ions with bicarbonate, (2) the reaction of hydrogen ions with filtered buffers such as disodium salt, (3) reaction with ammonia, and (4) excretion of the free hydrogen ions.

Factors that affect enzyme assays include temperature, pH, substrate concentration, and time of incubation. For each clinically important enzyme, the optimum temperature and pH for its specific reaction are known. When lower than optimum temperature or pH is employed, the measured enzyme activity will be lower than the expected activity value. As temperature increases, the rate of the reaction increases. Generally, a twofold increase in reaction rates will be observed with a 10°C rise in temperature. However, once the optimum temperature is exceeded, the reaction rate falls off as enzyme denaturation occurs at temperatures ranging from 40 to 70°C.

In a state of acidosis there is an increased amount of hydrogen ions that combine with albumin. Because H ions are combining with albumin, less albumin is available to bind to calcium; therefore ionized calcium levels increase.

Enzyme assays are recommended to be performed during the linear phase, so that a consistent
change over time can be used to calculate the enzyme concentration.

Assuming that a screening test is abnormal, a definitive stimulation test is often performed. The definitive test involves looking at the growth hormone response after intravenous insulin infusion.

Amido black 10B, Coomassie brilliant blue, and Ponceau S are dyes that are used to stain serum proteins after electrophoresis. Once the serum protein bands are stained, they may be quantified by scanning the support media at the appropriate wavelength with a densitometer. Oil red O and fat red 7B are dyes that are used to stain lipoproteins following electrophoresis.

The serum proteins are divided into five principal fractions based on their electrophoretic mobilities. The five fractions are albumin, alpharglobulin, alpha2-globulin, beta-globulin, and gamma-globulin. Albumin constitutes the largest individual fraction of the serum proteins. The reference concentration of albumin in serum ranges between 3.5 and 5.0 g/dL, and the total globulin concentration is between 2.3 and 3.5 g/dL.

Creatine kinase (CK) is found mainly in skeletal muscle, cardiac muscle, and brain tissue. Mg2+ is required as an activator. The direction in which the reaction takes place, and hence the equilibrium point, depends on the pH. Measurement of CK activity is valuable in the early diagnosis of acute myocardial infarction. Its level rises 4 to 6 hours after infarction, reaches its peak at 12 to 24 hours, and returns to normal by the third day. In addition to quantifying total CK activity, electrophoresis may be performed to ascertain the presence of an MB band, which represents the heart tissue isoenzyme.

Osmolality and specific gravity both measure the solute concentration of a solution. Specific gravity measures solute concentration as the solute’s density, which is subject to interference from large molecules such as glucose and proteins. Osmolality, on the other hand, measures solute concentration as the number of molecules present by measuring the number of molecules per kilogram of water.

Bilirubin will deteriorate when exposed to either white or UV light. This deterioration is also temperature sensitive. Thus, specimens for bilirubin analysis should be stored in the dark at refrigerator temperature until the assay can be performed. Lipemia should be avoided, due to its interference with spectrophotometric analyses. Because hemoglobin reacts with diazo reagent, use of hemolyzed specimens should be avoided. Hemolysis will cause bilirubin results to be falsely low.

The anion gap, especially when elevated, is useful in diagnosing the type of metabolic acidosis and in indicating if a mixed disorder exists.

Four bilirubin fractions represented by Greek letters have been identified: unconjugated (alpha), monoconjugated (beta), diconjugated (gamma), and unconjugated bilirubin covalently bound to albumin (delta). Delta-bilirubin is normally present in low concentration in the blood, and it is known to react directly with diazotized sulfanilic acid. Increased serum levels of delta-bilirubin are associated with liver-biliary disease.

Marked increases in triglyceride levels, between 1000 and 2000 mg/dL have been associated
with increased risk for the development of pancreatitis.

The concentration of total protein in cerebrospinal fluid (CSF) is 15^5 mg/dL. Such a low level of protein requires a method with sufficient sensitivity such as Coomassie brilliant blue. Turbidimetric methods can also be used to quantify protein in CSF. Neither biuret nor Ponceau S has the sensitivity needed, and bromcresol green measures only albumin and does not react with the globulins.

Whole blood glucose levels are 12% to 15% lower than plasma glucose levels. Therefore a plasma glucose level of 100 mg/dL would roughly correspond to a whole blood level of 85 mg/dL.

The free thyroxine (FT4) index is calculated as follows:

Estrogens are a group of steroids responsible for the development of female sex organs. The estrogens include estrone, estradiol, and estriol. Estradiol is the predominant form of estrogen.

Symptoms are sometimes nonspecific, making it difficult to diagnose congestive heart failure. B-type (brain) natriuretic peptide (BNP) is used to determine if physical symptoms are related to congestive heart failure. BNP is synthesized in and secreted by myocardial ventricles in response to ventricular volume expansion and pressure overload. An increase in BNP causes dilation of blood vessels and promotes sodium and water loss by the kidneys. This reduces fluid load on the heart in an attempt to improve cardiac function. Albumin cobalt binding is a test that measures ischemia-modified albumin, which is a marker for ischemic heart disease.

Ampholytes are mixtures of polyanions and polycations used to establish a pH gradient within the gel media in isoelectric focusing. When an electrical field is applied to the gel, ampholytes seek their own isoelectric point where they become stationary, establishing a pH gradient. Similarly, proteins will migrate within the gel-gradient until they reach the pH of their isoelectric point, thus becoming stationary or focused. This system is most useful in separating proteins that have close isoelectric points.

The heme protein myoglobin can bind oxygen reversibly and is found in cardiac and striated muscles. In cases of acute myocardial infarction, myoglobin increases within 1-3 hours of the infarct. Myoglobin is not cardiac specific, and increased serum levels also occur in vigorous exercise, intramuscular injections, rhabdomyolysis, and muscular dystrophy. Because myoglobin is a relatively small protein and able to be excreted by the kidneys, elevated serum levels occur in renal failure.

The cells of the reticuloendothelial system are able to phagocytize aged red blood cells and convert the hemoglobin to the excretory product bilirubin. It is then necessary for the bilirubin to be transported to the liver, where it is conjugated for excretion in the bile. Albumin acts as the transport vehicle for unconjugated bilirubin in the blood, with each mole of albumin capable of binding two moles of bilirubin.

The oxidoreductases are enzymes that catalyze the addition or removal of hydrogen from compounds. These enzymes need a coenzyme, such as nicotinamide adenine dinucleotide (NAD+) or its phosphorylated derivative NADP+, as a hydrogen acceptor or donor in order to function. Lactate dehydrogenase and glucose-6-phosphate dehydrogenase are examples of oxidoreductases. Isomerases are those enzymes that catalyze intramolecular conversions such as the oxidation of a functional group by an adjacent group within the same molecule. Glucose phosphate isomerase is an example of this class of enzymes. Ligases are those enzymes that catalyze the union of two molecules accompanied by the breakdown of a phosphate bond in adenosine triphosphate (ATP) or a similar triphosphate. An example is glutamine synthetase.

C-reactive protein is an acute-phase reactant that is increased in the presence of inflammation. High-sensitivity C-reactive protein (hs-CRP) refers to a sensitive method that is able to measure low levels of CRP in serum. One theory is that elevated levels of CRP contribute to the damage of arterial walls that precedes plaque formation. hs-CRP is considered a good predictor test for assessing cardiovascular risk. However, it is also elevated in other conditions, including infection, stress, and trauma.

Although lipoproteins can be assayed using a variety of anticoagulants, the preferred anticoagulant is ethylenediaminetetraacetic acid (EDTA) because it preserves lipoproteins over time.

A decrease in ventilation would cause the accumulation of the acidic gas PCO2, causing respiratory acidosis.