CLINICAL CHEMISTRY
Which parameters are calculated by the blood gas analyzer
HCO3- and base excess
Calculate Total CO2 content
HH equation: pH = 6.1 + log [HCO3- /(0.031 x pCO2)] TCO2 = HCO3- + (0.031 * pCO2) (Reminder: TCO2 is roughly 5% higher than HCO3-)
Diagnosis diabetes mellitus
Hgb A1c > 6.5% Fasting plasma glucose (FPG) > 126 mg/dL 2 hr plasma glucose > 200 mg/dL during an oral glucose tolerance test
general causes of Hypercalciuria and Hypocalciuria
Hypercalciuria: primary hyperparathyroidism, malignancy, endocrine disorders Hypocalciuria: hypoalbuminemia, chronic renal failure, magnesium deficiency
Describe the difference between Integrated Multisensor Technology (IMT) and Ion Selective Electrode (ISE) for measurement of electrolytes?
ISE use membrane potentials to selectively interact with a single ionic species but IMT can simultaneously measure multiple ions instead of just one.
How are Absorbance and %T related mathematically?
A=2-log(%T) (Absorbance = 2- log (percent transmittance))
What are some functions of intracellular calcium?
- Muscle contraction - Hormone secretion - Glycogen metabolism - Cell division A decreased concentration of serum free calcium causes increased neuromuscular excitability and tetany. The measurement of free calcium is accomplished using ISE. These need to be temperature controlled to maintain the samples at 37 C. Extracellular calcium has a greater concentration than intracellular calcium and is mainly needed for bone mineralization and blood coagulation.
Briefly describe the working principle of this instrument. Include all electrodes and their purposes.
- Potentiometry: potential of the electrode chain is recorded with a voltmeter and related to the concentration of the sample (Nernst equation) o pH, pCO2, electrolytes (ISE) - Amperometry: the magnitude of the electrical current flowing through an electrode chain is proportional to the concentration of the substance being oxidized or reduced at an electrode. o pO2, glucose A reference electrode is used to provide a stable potential against which the other potential differences can measure. (Clark O2 electrode)
Briefly describe a method for quantification of total calcium in serum/plasma:
- Spectrophotometric methods: metallochromic indicators that change color when they bind calcium, less accurate, easier to automate ARSENAZO RXN - Ion specific electrode methods (ISE): specimen is acidified to convert protein bound and complexed calcium to free calcium before measuring the total calcium - Atomic absorption: AAS, remember that the atom is in a ground state...it absorbs the energy, and we measure the change in absorption. We do not measure any return to ground state. That would be a different method, emission spectroscopy, which we don't use to measure calcium.
controls may concentrate overtime due to evaporation, or decrease over time due to denaturation. What actions could we take to prevent these things from happening, and/or extend the stability of the control? (list three)
- Store in proper air-tight container, either refrigerated or at room temp, or freezing if this doesn't alter the substances - Have expiration dates visible and make sure they are checked before use - Mix all controls prior to use to prevent any concentration at the bottom of the container, if frozen make sure to vortex for a homogenous mixture
the two clinical settings in which lactic acidosis can occur
- Type A (hypoxic) associated with decreased tissue oxygenation, such as shock, hypovolemia, and left ventricle failure. - Type B (metabolic) associated with diseases (diabetes mellitus, neoplasia, liver disease), drugs/toxins (ethanol, methanol, salicylates), inborn errors of metabolism.
What is the equation utilized in spectrophotometry that includes absorbance, path length, molar absorptivity constant, and concentration, to relate concentration and absorbance?
A= E×b×c (Absorbance= molar absorptivity × length of light path × concentration of absorbing molecules)
In chronic renal failure, hypocalcemia is due to a combination of:
1. hypoproteinemia 2. hyperphosphatemia 3. low serum 1,2 (OH)2D
Calculate the bilirubin concentration of the following samples, if the 10 mg/dL standard reads 0.30: 0.30 A
10 mg/dL
Calculate the bilirubin concentration of the following samples, if the 10 mg/dL standard reads 0.30: 0.80 A
27 mg/dL
Calculate the bilirubin concentration of the following samples, if the 10 mg/dL standard reads 0.30: 0.15 A
5.0 mg/dL
calcium exists in three states in plasma
50% free or ionized, 40% bound to plasma proteins (albumin), and 10% complexed to small anions.
What is the reference interval for serum/plasma total calcium? What is the linearity of this method?
8.5-10.2 mg/dL (x2 dilution) 1-13 mg/dL
End stage renal disease
Abnormalities of kidney structure or function GFR < 15 mL/min/1.73 m
How are the aminoglycosides and vancomycin administered? Why?
Aminoglycosides are administered intravenously or intramuscular due to poor oral absorption
What are some toxic effects of the aminoglycosides?
Aminoglycosides are administered intravenously or intramuscular due to poor oral absorption, and the elimination is largely renal with minimal metabolism, so kidney dysfunction is a concern and may require dosing adjustments. They are also associated with risk of serious toxicity including nephrotoxicity (renal tubular necrosis) and ototoxicity (auditory nerve degeneration).
What tests are included in Prenatal Risk Screening and what is each screening for?
Amniocentesis for measurement of AFP and acetylcholinesterase in amniotic fluid = Neural tube defect Maternal serum AFP: lower levels, Unconjugated estriol (uE3): lower levels, CG: higher levels, Inhibin A (inhA): higher levels = Down syndrome
What is often used to check the linearity of detector response in a spectrophotometer?
An absorbance vs concentration graph should be plotted to determine the linearity as well as sensitivity. Checked with standard absorbing solutions: chemical solutions (colored solutions with a specific absorbance), cobalt chloride, nickel sulfate, potassium chromate Filters: didymium filter (for broader band pass), holmium oxide (for narrow bandwith instruments)
Acetaminophen and Salicylate
Analgesics (pain relievers)Antipyretics (fever reducers)
Carbamazapine, Phenytoin, Phenobarbital Valproic Acid
Antiepileptics (treating seizures)
Amikacin, Gentamicin, Tobramycin, Vancomycin
Antimicrobial
Lithium
Antipsychotic (mood-stabalizing)
What is the physiological role of bicarbonate (measured as total CO2)? What is the chemical equation relating it's major role?
Bicarbonate is the most important buffer of plasma, its effectiveness is based on high concentration and that the lungs can readily dispose of or retain CO2 (20:1 ratio) HCO3¯ + H+ (kidney)--> H2CO3 --> CO2 + H2O (lung) Oxygen has a higher affinity for hemoglobin to transfer to tissues, then transfers with CO2 back to the lungs
Ca/Phos/Vit D2 and D3 process and how it's impacted by parathyroid hormone pathway
Bone: Osteoclasts resorb bone to deliver calcium into the ECF PTH causes bone to be resorbed, followed by an increase in bone formation Increase plasma Ca and Phos Kidney: PTH enhances calcium reabsorption in the DCT and reduced calcium excretion Decrease Ca and increases Phos excretion (Increase plasma calcium, decrease plasma phos) Increase Vit D activation Intestine: PTH stimulates intestinal transport of calcium and phosphorus indirectly via 1,25 dihydroxy-vitamin D (calcitriol) Increase Ca and Phos adsorption (increase plasma Ca and Phos) Overall increase in Ca and decrease in Phos
Theophylline and Caffeine
Bronchodilators (neonatal apnea)
Digoxin, Procainamide/NAPA, and Lidocaine
Cardioactive (antiarrhythmic agents)
Urea
Chemical; diacetyl monoxime or enzymatic methods which quantify ammonia that was hydrolyzed from urea with urease Interferences: - Endogenous ammonia interference: aged samples, some urines, certain metabolic disorders (falsely increase) - Sodium fluoride (enzyme inhibitor) DON'T use for any enzyme measurement (grey top tube)
What are the specimen requirements and special handling process for ABGs?
Collected in a heparinized syringe, it should be filled completely without airspace or bubbles and handled anaerobically, to prevent metabolism from continuing the sample should be kept on ice slurry and rotated to keep the sample homogenous. Bubble = lower CO2, Higher O2 CO2 diffuses out of sample, O2 into sample No ice increases CO2 due to metabolism
Total bilirubin
Colorimetric reaction, Conjugated (directly measured) + unconjugated (indirectly measured) Diazo Reagent (measures the soluble, conjugated bilirubin) + Caffeine-benzoate reagent (measures the insoluble, unconjugated bilirubin) Total bilirubin Interferences: - Light (breaks down bilirubin) - Room temp (increases degradation) - Hemolysis (deoxyhemoglobin decreases the reaction of bilirubin with diazo reagent = falsely low) - Lipemia (error in spectrophotometric reading) - Icterus (depends on measured wavelength, since bilirubin is measured at 450 nm, so icterus would be affecting results at that wavelength)
Cuvette:
Contains the sample and has a constant light path to maintain the relationship in Beer's Law
Unassayed vs assayed controls
Controls can either be assayed (known value of what is contained = use to monitor accuracy of methods) or unassayed (presence is known but not quantity = cheaper) depending on the method being analyzed. Controls should have the same matrix of the samples being tested. With unassayed we still have to determine the concentrations, but we run samples over a timeline and get the average concentration ourselves, establishing our QC ranges as we go, versus the assayed types which are prepackaged and have listed concentrations.
Detector:
Convert transmitted radiant energy into electrical energy
Sweat chloride uses which type of electrochemical detection? What disease state are we looking for, and what is the physiological problem that causes the disease?
Coulometry: a titration that makes use of an electrochemically generated titrant via constant current. - Chloride titration, Cotlove titrator for chloride analysis in cystic fibrosis, which has the defect of transmembrane conductance regulator protein
What do we use to account for stray light which may be outside of the narrow bandpass transmitted by the monochromator?
Cutoff filters
Meter:
Digital display allowing the user to interpret results, by converting the electrical energy into a viewable form
difference between direct and indirect ISE. What are the limitations we need to be aware of for each?
Direct ISE: The patient sample in in direct contact with the electrode and it measures the molality (moles of ion per mass of water) of the analyte as well as the activity (the concentration of free unbound ion in solution). It is not affected by any variation in the concentration of lipids or proteins in the sample. Indirect ISE: The sample is diluted with a buffer, and the concentration of the ion is measured. However, since the amount of lipids and proteins may vary in unhealthy individuals (diabetes, hyperprotienemia, hyperlipidemia) the concentration may vary from the molality of the sample due to the dilution step, this may cause pseudohyponatremia.
Absorption:
Drugs are either administered intravenously or orally or cutaneous or intramuscularly. Intravenous delivery directly inputs the drug into circulation, but oral consumption must first pass through the GI tract and then be absorbed into the vascular system. The compound dissociates into the digestive fluids where it crosses through cell membranes and enters the bloodstream. The amount of drug absorbed relative to the quantity given is the bioavailability.
How does the energy of a photon mathematically relate to frequency and wavelength?
E= hc/v (Energy = (planks constant (6.62×10-27) × speed of light)/ wavelength) Inversely proportional to wavelength
Briefly describe the principle of molecular fluorescence for analysis, including basic instrument layout. Please label and describe specifically the difference between the excitation wavelength and the emission wavelength. What is the path of light through the instrument, and what's the change in energy from excitation to emission?
Fluorescence occurs when a molecule absorbs light at one wavelength and emits light at a longer wavelength. Light source -> Entrance slit -> Monochromator -> Exit slit -> Cuvette (Light from light source exits ) -- 90 degree angle) --> Entrance Slit -> Monochromator -> Exit Slit -> Detector -> Meter The difference between the excitation and emission wavelength is that excitation wavelength is shorter than the emission wavelength The difference between the excited energy and emitted energy is that more energy is used to excite the photon and photon emitted has less energy (since some of the energy is absorbed by molecule in the form of vibrations)
Exit slit:
Focuses the monochromatic light on the sample
Which form of calcium is biologically active?
Free Calcium.
how to plot LJ plots
Given a list of numbers follow these steps: 1) Calculate the mean and the standard deviation 2) Mean +2 SD 3) Mean -2 SD 4) Step 2 and 3 show the "target range" (round to the original amount of decimals in the list) 5) Fill out the y axis of the Levey-Jennings plot with the mean and +/- 3 SD on both sides and the x axis with the days 6) Plot the values for each day and connect the dots
Briefly describe the principle of atomic absorption spectrophotometry. Be sure to include the most common light source, and the purpose of the flame.
In AAS, the flame forms free ground state atoms (small ionized pieces of the larger element...think Cd2+ flying around. The hallow cathode lamp is the same energy, so when that energy frequency hits the Cd2+, those cadmiums absorb that energy. This means there is less transmitted energy on the other end of the sample, and increased absorbance...meaning we've got more Cd in the sample. Atomic absorption detects the absorption of the atoms instead of the molecules Most common light source: Hollow cathode lamp Flame: forms free ground state atoms
If you change the path length of the cuvette: what effect does this have on %T, Absorbance and concentration of the sample?
Increase the cuvette length = Decrease transmittance, Increasing absorbance, concentration remains constant Decrease the cuvette length = Increases transmittance, Decreases the absorbance, concentration remains constant
Why is it important to transport an ionized calcium specimen on ice? Specifically, what are the effects on pH and ionized calcium?
Ionized calcium is directly related to the pH of the sample, if the sample is kept at room temperature the metabolic processes will continue anaerobically which decreases the pH, falsely increasing the ionized calcium measurement, the ice slows the metabolic process which keeps the pH constant and makes the calcium measurement more reliable.
What effect would an air bubble in the syringe have on a specimen for pH and ionized calcium that was transported on ice?
Ionized calcium should be collected anaerobically to keep the pH constant, if an air bubble is in the sample, CO2 will be lost from the sample and this will increase the pH which in turn decreases the ionized calcium.
List examples of potentiometric (ISE) electrodes? (i.e. Na+)
K+, Na+, Cl-, Ca 2+, Li+, Mg+, CO32-
What roles do the kidneys play in assisting bicarbonate in its buffering ability and briefly describe how each works?
Kidneys: Renal excretion of acids and conservation of bicarbonate occur through: - Na+-H+ exchange, can also excrete K - Production of ammonia and excretion of NH4+ (ammonium) --> can't excrete ammonia, more acidic because you aren't getting rid of a H when you bind NH4 which is the excreted form - Reclamation of bicarbonate
How would a large amount of stray light affect absorbance accuracy? What concentration of analyte would be most affected?
Large amount of stay light would decrease the accuracy of the absorbance at higher concentrations.
please sketch and explain a basic spectrophotometer
Light Source -> Entrance Slit -> Monochromator -> Exit Slit -> Cuvette -> Detector-> Meter
Acetaminophen may cause severe toxicity to what organ when consumed in overdose quantities?
Liver! Acetaminophen is normally metabolized in the liver. (May cause sever hepatic and renal toxicity when consumed in overdose quantities) Reyes syndrome
What roles do the lungs play in assisting bicarbonate in its buffering ability and briefly describe how each works?
Lungs: Absorption of O2, maintenance of normal pH through elimination or retention of CO2 ("ventilation"), and diffusion of O2 and CO2 across alveolar and cell membranes which is governed by gradients in the partial pressure of each gas. Respiratory response to acid base changes is immediate and can lead to hyperventilation. COPD: cant blow off as much CO2 --> acidotic
Metabolism (biotransformation):
Metabolism is the biotransformation of a compound (endogenous or exogenous) and enhances excretion by increasing water solubility (addition of soluble moiety like -OH or others). Drug metabolism is usually the result of enzymatic activity which can either be first order (dependent on drug concentration) or zero order (dependent on enzyme amount and metabolic capacity). Induction refers to enhanced metabolic activity due to increased expression of drug-metabolizing enzymes. Much happens in the liver, which is why toxins, and compounds that need lots of transformation take a heavy toll on the liver
Entrance slit:
Minimizes stray light and focusses the light on the monochromator and limits the total radiant energy reaching the sample and photo cell
describe the working principles of the main immunology analyzer
Multiple different immunoassays including sandwich, chemiluminescent, competitive, monoclonal antibody covalently bond to paramagnetic particles
Lactate
NADH (reduced form) is measured spectrophotometricly (wavelength: 340 nm) after lactate is oxidized to pyruvate in the presence of NAD+ Increase at 340 nm: latate pyruvate loosing election giving to NADH Interferences: - Patient not fasting and at complete rest (allows lactic acid concentrations to reach a steady state) - Tourniquet (hemconcentration) - Not collected with heparin, spun, and refrigerated (lactate increases when in blood due to glycolysis)
f a STAT potassium came down to the lab and our results showed a value of 6.7 mg/dl, what should your course of action be before reporting? Or should you simply report the results? Would your actions be different if the results were 7.5 mg/dL?
NL potassium range: 3.5-5.5 mg/dL Potassium is the major intracellular cation, so hemolysis may falsely increase the result, the sample should be examined for hemolysis before reporting a result that is very high. If no hemolysis found, check patient status and age group (newborns are high) Sample types must be from serum or citrate tubes since EDTA is potassium EDTA which will falsely increase the potassium levels
Distribution
Once the drug has been absorbed into the bloodstream, it is distributed and spread throughout the systemic circulation and into various tissues. Some remain in the blood plasma, others localize to specific tissue, their distribution depends on the molecular size, degree of ionization, lipid solubility, protein binding, and composition.
Which commonly used electrode is based on the principle of amperometry?
PO2 electrode (Clark oxygen electrode) - Measurement of current flowing through an electrochemical cell when a constant potential is applied
The concentration of free calcium in the plasma is regulated by
PTH and 1,25(OH)2D.
Phase I and Phase II biotransformation reactions that occur in the liver
Phase 1: chemical modification (redox, hydrolysis) Phase 2: conjugation to another molecule (glucuronic acid, billirubin) (Names do not indicate order)
Diabetes insipidus
Polyuria in which volume exceeds 3 liters per day causing dehydration and great thirst, emancipation and hunger. Dilute urine < 250 mOsmol/L Central: decreased or absent ADH secretion Nephrogenic: renal resistance to ADH
Light Source
Provides desired wavelength and enough energy to penetrate the solution "Radiant energy source that will be absorbed by the analyte of interest"
Describe the principle of freezing point depression used to measure osmolality?
Sample is super cooled while being stirred, as the stirring accelerates the water molecules crystalize to form a slush, the released heat of fusion initial warms the sample then plateauing causing an equilibrium of freezing and thawing. The observed freezing point is measured and used to calculate the osmolality of the sample.
Why would it not be a good idea to draw blood levels during the distribution phase?
Since the distribution phase involves the drug traveling throughout the body in the plasma, the drug has not reached the equilibrium position and thus the concentration measured may be skewed. Also, there may be some areas of the body (close or far from the point of drug absorption) that may show higher or lower measurements than another area.
What are the major solutes that contribute to serum osmotic concentration? List the equation for Osmolality?
Sodium (about half of total osmolality), glucose, urea (sometimes: chlorine, bicarbonate) Posm = 2(Na+) + (glucose/18) +(BUN/2.8) Other things that can significantly impact this are things like alcohols (think poisoning)
Monochromator:
Spectral isolation that only allows a specific wavelength to pass through
describe the working principles of the main chemistry analyzer
Spectrophotometric method, enzymatic assays, uses IMT
What is the method for quantification of total calcium in urine?
Spectrophotometry, Arsenazo-III
describe the effects of various substances such as uric acid, ascorbic acid, bilirubin, hemoglobin, tetracycline, and glutathione on the peroxidase step in a glucose oxidase/peroxidase coupled reaction for measuring glucose.
Substances that interfere with the enzymatic reaction or strong reducing agents like uric acid, ascorbic acid, bilirubin, hemoglobin, tetracycline, and glutathione prevent oxidation of the chromogen by competing with if for hydrogen peroxide which produces false negative results. Contamination with oxidizing substances or peroxidase can cause a false positive result since the reaction requires these to go forward.
Phenobarbital and primidone please have an understanding of peak and trough measurements here. What should therapeutic range measurements look like and why do we care clinically?
The optimal therapeutic concentration of primidone has been established as 5-10 mg/L Concurrent analysis of phenobarbital is required for complete interpretation of results, evaluating the ratio of phenobarbital to primidone may assist with detection of noncompliance
Standard Deviation Interval
The estimated range of values that fall within 1, 2, or 3 standard deviations. 1 SD: 68%, 2 SD: 95%, 3 SD: 99.7%
Elimination:
The final removal of the drug from the body is called elimination and the most common form of excretion is through the urine or the stool. Clearance of the drug can be measured directly, or the renal elimination can be estimated using the glomerular filtration rate. However, urine is rarely used to monitor drug concentrations. (because it will likely be concentrated...what the kidney does)
Why is caffeine given to neonates?
Therapy with caffeine is effective in the treatment of neonatal apnea. (popular because of its long half-life in neonates)
What are the ideal characteristics of a control material?
There should be at least 2 levels of controls where the concentrations are focused on medical decision points, there should also be enough quantity and quality of the control so that it will last a year and fit in a convenient size for easy storage. (Can aliquot and extend life by freezing, as long as it doesn't affect pression or accuracy of the known analyte concentrations).
diabetes mellitus
Type 1: cell mediated autoimmune destruction of the insulin - secreting cells of pancreatic beta cells (inherited) Type 2: decreased ability of insulin to act on periferal tissue (insulin resistance) OR beta cell disfunction which is an inability of the pancrease to produce suficent insulin to compensate for the insulin resistance
How do the reference intervals for Urine (Random 50-1200 mOsm/kg, average 500-800) versus Serum (275-295mOsm/kg) osmolality help you remember the physiology of the kidney, and the clinically significant situations where measurement of osmolality might be useful? List three of these situations.
Urine has a much larger range than serum which shows how well the kidneys filter and regulate the serum and excrete what isn't needed in the urine. These measurements relate to water homeostasis and the degree of intra and extracellular volume and tonicity and can be used in diagnosing metabolic, endocrine, and renal disorders.
Controls
Used to monitor the performance of a method after it has been calibrated, they are run with or before patient samples and the ranges give a guideline for acceptable results. They are used to preform QC. Measure of accuracy, compound composed of known concentrations of material with similar matrix to the desired sample type
State the antibiotic embedded in the membrane of the K+ electrode?
Valinomycin
Below is a Spectral transmittance curve for analyte X. What wavelength should measurements be made at? Why?
Wavelength should be measured at 500 nm because this is where the analyte has the lowest transmittance which is inversely proportional to the absorbance so that is where here would be peak absorbance
Osmolatlity and ADH
When serum osmolality increases, your body releases ADH. This keeps water from leaving in the urine, and it increases the amount of water in the blood. The ADH helps restore serum osmolality to normal levels. If you drink too much water, the concentration of chemicals in your blood decreases.
You perform daily maintenance, Calibration, and QC on your chemistry analyzer. You notice that three of your assays have 1-2S QC flags. You should review the Levey Jennings charts to determine what action to take. You notice a trend downwards in the QC values over the last 8 QC points.
a. This is an example of gradual error, TREND (not a shift) b. This could be caused by: deterioration of reagents/ standards, gradual change in instrumental performance, aging light source (List two examples and describe the actions you'd take for each) - Check reagent expiration dates, and replace them if needed - Examine maintenance log to confirm it has been kept up to date, may need to use the manual or call manufacture if the problem cannot be solved - Change light source
Zero order kinetics
also called nonlinear kinetics, which occurs when there is an excess concentration of drugs and this exceeds the available metabolic capacity (drug overdose). In this case the enzyme is the rate-limiting factor and the rate of metabolism is independent of the drug concentration.
Standards (Standard Curve)
are used to plot a standard curve which is part of the calibration process of an instrument. This curve can then be used during quality control to ensure the controls land on the curve.
Primary hyperparathyroidism is the most common cause of elevated...
calcium levels in outpatients.
First order kinetics
excess metabolic capacity is available, so the rate of metabolism depends primarily on the drug concentration and can lead to a log-linear representation of drug concentration vs time and is expressed in terms of half-life, the time required to metabolize 50% of the drug present.
glucose method for serum
hexokinase (the gold standard)
Low total serum calcium...
hypocalcemia is caused by a decreased albumin-bound fraction or the free fraction or both. Hypoalbuminemia is the most common cause of decreased total calcium with normal free calcium.
spectrophotometric detectors from most complex to simple complex
i. Photodiode ii. Photomultiplier tube iii. Phototube iv. Photovoltaic cell v. Thermal
monochromators from least efficient to most efficient.
i. Plastic/glass ii. Interference filter iii. Multiple interference filters iv. Prisms v. Diffraction gratings
clinically significant situations where measurement of osmolality might be useful? List three of these situations.
i. Toxins / Medication: osmolality can help screen for low molecular weight toxins in the serum and be used to determine the optimal dosage of medication while avoiding renal damage. ii. Hydration: this is useful for patients where hydration is hard to determine (like people in a coma) so osmometry can quickly asses if they are over or underhydrated, this is also helpful with burn patients who need their fluids and electrolytes monitored. iii. Renal Dialysis: Renal disease increases serum osmolality so osmometry can be used to monitor how affective the treatment is.
Sample collection for iCa
iCa2+ specimens must be collected under anaerobic conditions to avoid loss of CO2 and pH increase. Any significant time delay between collection and iCa2+ measurement if left at room temperature can cause hypercalcemia due to metabolic activity that causes a drop in pH. Freezing the sample will cause the pH to increase, falsely decreasing the calcium measurement.
Standard Deviation
measure of precision, (s) it is the square root of the variance and expressed in the same units as mean, median, and mode. Measure of precision
glucose on the dipstick
oxidase peroxidase
Briefly describe the relationship between ionized calcium and pH in an ionized calcium sample
pH change is inversely proportional to the concentration of iCa2+. At a low pH there is an increase in circulating hydrogen ions, which competes with the free calcium ions binding to albumin. An increase in H+ displaces Ca2+ from binding sites on albumin and the amount of iCa2+ increases. When the blood pH increases, with decreased H+, albumin and the globulins become more negatively charged and bind more calcium, causing the measured amount of iCa2+ circulating to decrease. **For each 0.1 change in pH, ionized Ca changes by ~5%
Which parameters are actually measured in the blood gas analyzer?
pH, pCO2 and O2
The study of the rate processes of absorption, distribution, metabolism (biotransformation), and elimination of drugs or chemicals is called
pharmacokinetics
Phenobarbital is a metabolite of
primidone
Mean
the arithmetic average value calculated as the sum of all individual values divided by the number of values (x bar). It is a measurement of central tendency of distribution of data.
Range
the range of all direct analyte measurements in a method without any manipulation of a sample. It is found by taking the difference between the highest and lowest values.
What is a "MoM"? How is it used?
the ratio between the patient's result and the median result appropriate for the gestational age of the fetus and is used to screen the AFP (alph-fetoprotien) level at the different age of the fetus in comparison to the laboratory established median for each marker. Used to quantify the "risk of developing" the disease or condition being screened for
Coefficient of Variation
the standard deviation expressed as a percentage of the mean, (CV) it is often used to express the variation of an analytical method in units independent of the method to determine which method has the best precision.
Median
the value at the center of all the observations, with an equal number above and below it when ordered from low to high. In a symmetrical distribution the median equals the mean and is a measurement of the central tendency.
Mode
the value in the sample of population that occurs with the greatest frequency. In a symmetrical distribution the mode equals the mean and the median. In an asymmetrical distribution with more than one central tendency a secondary mode exists and is bimodal.
Relative Standard Deviation
used to determine whether the standard deviation is large or small compared to the mean of the data set (RSD), it is found by dividing the standard deviation by the mean.
