Final Practical

Perform serum calcium analysis using a colorimetric method
To perform serum calcium analysis using a colorimetric method you first have to label the tubes and then add calcium reagent to each tube. Then add fluid to each tube (as labeled), and mix and incubate. You then measure the absorbance at 550nm and calculate the concentration of calcium in each sample
Identify sources of error for the serum calcium analysis
The sources of error for this method are contaminated glassware (with calcium), high bilirubin or hemoglobin (false lows); hemolyzed specimens must be analyzed with EGTA
Perform serum magnesium analysis
The serum magnesium analysis is performed by labeling the tubes and then adding reagent to each tube, then adding appropriate sample to each tube, mixing and incubating. The samples are then put in the spectrophometer and read at 520nm
Identify sources of error for serum magnesium analysis
The sources of error for this method are glassware contamination, EGTA interference, organic ion interference, and hemolysis
List the three physiochemical forms of calcium found in plasma and the approximate percentage of each.
(1) free (ionized), (2) Bound to plasma proteins, and (3) complexed with small anions. Free calcium makes up 50% of all total calcium, bound calcium makes up 40% of total calcium and complexed calcium makes up 10% of total calcium.
Explain why samples for ionized calcium levels are collected anaerobically.
Samples for ionized calcium are collected anaerobically in order to preserve the pH of the sample. Calcium is very dependent on pH in that if there is an increase in pH there will be an increase in protein-bound calcium which in turn causes it to look like there is lower free calcium then actually present in vivo. Anaerobic collection prevents the loss of CO2 which would increase the pH yielding invalid results.
What is the purpose of CPC
common indicator, used to complex with calcium in an alkaline solution to form an intense chromophore which can be detected via spectrophotometric methods. Absorbance is directly proportional to concentration
What is the purpose of 8-hydroxyquinoline
complexes with magnesium to remove magnesium from the reaction
What is the purpose of Potassium cyanide
used to block heavy metal interference
What is the purpose of Ethanol
used to decrease the absorbance of the blank
What is the purpose of EGTA
used as the blank when testing hemolyzed specimens
What is the major source of error in our calcium procedure?
The major source of error in this calcium procedure is glassware contamination with calcium.
List the equation used to correct total calcium values when serum albumin levels are abnormal.
Corrected calcium (mg/dL) = Total Calcium (mg/dL) + 0.8 (4- Albumin [g/dL])
What is the physiological significance of magnesium?
The physiological significance of magnesium is in magnesium’s action as a cofactor for important enzymatic reactions, as a reactant in metabolic reactions (with ATP), as a part of nucleic acid synthesis and as an allosteric activator of enzymes.
Name two conditions associated with hypomagnesemia.
Two conditions associated with hypomagnesemia are (1) malabsortion due to alcoholism or (2) urinary loss from kidneys due to diabetes mellitus.
Name two conditions associated with hypermagnesemia.
Two conditions associated with hypermagnesemia are (1) due to excessive intake via antacids or (2) renal failure in which magnesium cannot be removed from circulation.
Name two methods other than spectrophotometric methods that may be used for magnesium determination.
ISE’s and Atomic absorption
What effect does hemolysis have on magnesium levels and why?
Hemolysis allows for the high levels of intracellular magnesium to pour out into the serum. This will cause the test results to seem very high, when they actually could be low or normal because you will be measuring the magnesium that is supposed to be inside the cells, not in the serum.
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