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Clinical Chemistry 2 > Lab Study 1 > Flashcards

Lab Study 1 Flashcards

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1
Q

What can the lab offer to aid the primary care giver in determining the patient’s risk of developing heart disease?

A
  1. Lipoprotein Profile (LPP)

2. Lipid Panel (LIPP)

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2
Q

What is the result of high levels of Low-Density Lipoprotein Cholesterol (LDL-C)?

A

Double’s a person’s risk of heart disease and excess LDL-C builds up in the walls of arteries forming plaque and fatty deposits resulting in atherosclerosis that limits blood flow to a person’s heart, brain kidneys, other organs and legs.

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3
Q

What is HDL-C and its nickname? Why?

A

HDL-C = High Density Lipoprotein Cholesterol.

“Good cholesterol” as it helps to remove excess cholesterol from the body.

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4
Q

What tests are part of the Lipoprotein Profile?

A
  1. Triglycerides
  2. Total Cholesterol
  3. HDL-C (High Density Lipoprotein Cholesterol)
  4. LDL-C (Low-Density Lipoprotein Cholesterol).
  5. Non-HDL Cholesterol
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5
Q

Is a non-fasting sample acceptable? When is it not?

A

Yes, non-fasting is acceptable.

Fasting for 8 hours is recommended for patients with previous triglycerides greater than 4.5 mmol/L.

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6
Q

When is the Friedewald formula for LDL-C calculation applicable?

A

Friedewald formula for LDL-C calculation is applicable for triglyceride concentrations < 4.6 mmol/L.

When triglycerides are > 4.6 mmol/L, LDL-C values risk being elevated due to presence of VLDL and chylomicrons.

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7
Q

What interfering substances does one need to be aware when performing the Lipoprotein Profiile?

A

Hemoglobin and bilirubin can interfere with enzymatic measurement of total cholesterol.

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8
Q

What is an osmometer used for in the medical lab?

A

An osmometer is used to measure the concentration of solutes within the sample via freezing point depression. This can provide useful information regarding patients electrolyte balance and the presence of acid-base disorders.

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9
Q

Is sodium an extra or intra _cellular ion? What is its purpose in the body and what is it used to assess?

A

Sodium (Na) - primary extracellular cation. Functions to maintain fluid distribution and osmotic pressure. Used to assess acid-base balance, water balance, and dehydration

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10
Q

Is potassium (K) an extra or intra _cellular ion? What is its purpose in the body and what is it used to assess?

A

Potassium (K) - primary intracellular cation. Functions to maintain critical nerve and muscle cell activity. Used to assess electrolyte balance, muscle weakness, cardiac arrhythmia, and renal failure.

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11
Q

How is Chloride used in the body?

A

Chloride (Cl) - primary extracellular anion. Functions to maintain body water distribution, osmotic pressure, and normal anion-cation balance. Used to assess acid-base balance, water balance, and dehydration.

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12
Q

What molecule is used in acid-base regulation?

A

Total CO2 (CO2) - buffering system that functions in acid-base regulation. Used in the diagnosis and treatment of acid-base imbalances in the respiratory and metabolic systems.

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13
Q

What is the most abundant mineral in the body?

A

Calcium (CA) - most abundant mineral in the body. Used to diagnose and manage a variety of disorders including bone, renal, parathyroid, and GI disease.

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14
Q

What are the many functions of Albumin in the body?

A

Albumin (AL) - constitutes 60% of the total serum protein and serves many functions including transport, binding toxic heavy metal ions, maintenance of serum osmotic pressure, etc.

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15
Q

Why is urea measured in the medical laboratory?

A

Urea (U) - end product of protein and amino acid metabolism excreted by the kidneys. Used to screen for renal function. Can be used in conjunction with creatinine to aid in diagnosis of pre-renal, renal, and post-renal hyperuremia.

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16
Q

What are the pre-analytical considerations that can impact accuracy of electrolyte analysis in the laboratory?

A
  1. Saline IV fluid contamination - falsely increased sodium and chloride values
  2. Contamination with K2 EDTA anticoagulant - falsely increased potassium value and falsely decreased calcium value
  3. Hemolysis - falsely increased potassium value

Samples that appear turbid, lipemic, hemolyzed, or contain particulate matter should be avoided.

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17
Q

What is osmality?

A

Osmolality, the concentration of solute particles; e.g. in a urine or plasma/serum sample.

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18
Q

What ions contribute the most to osmolality?

A

Sodium, chloride, and bicarbonate contribute the most to osmolality.

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19
Q

What are the standard units of osmolality?

A

The standard units are milliosmoles/kilogram (mOsm/Kg).

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20
Q

What is the physical principle that the osmometer works on at the RRC lab?

A

Colligative property of freezing point depression.

The greater the number of dissolved particles present in the sample the lower the freezing point of the sample.

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21
Q

What is the anion gap?

A

The anion gap represents the difference in charge concentration between the unmeasured anions and unmeasured cations. There is never a “gap” between the total cationic and anionic charges. The anion gap is created by the concentration differences between commonly measured cations (sodium and potassium) and commonly measured anions (chloride and bicarbonate).

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22
Q

What is the is the anion gap used to assess?

A

The anion gap can be used to:

  1. Assess instrument error - an abnormal anion gap on a “healthy” sample can indicate an instrument issue
  2. Presence of metabolic acidosis
  3. Indicate presence of unmeasured anions such as ketones or lactate
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23
Q

What is the equation for anion gap and its reference ranges?

A

Anion gap = Na - (Cl + TCO2) or (Na + K) - (Cl + TCO2)

Reference Range (without K+): 8 - 16 mmol/L

Reference Range (with K+): 12 - 20 mmol/L

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24
Q

What affects calcium concentrations in the blood sample?

A

Total calcium concentrations are affected by albumin concentrations. If a patient has hypoalbuminemia than their measured calcium concentrations will be lowered.

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25
Q

What is the equation to correct for Total Calcium (mmol/L)?

A

Corrected Total Calcium (mmol/L) = Measured Total Calcium (mmol/L) + 0.02 [40 - albumin (g/L)]

This corrected total calcium value can now be compared to the normal range for patients with a normal albumin of 40 g/L.

Note: Corrected calcium not calculated for patients < 18 years of age.

26
Q

What is the reference range for total calcium?

A

Total Calcium:

Reference Range: 2.10 - 2.60 mmol/L

27
Q

How can osmolality be estimated if equipment is not available to measure it?

A

By using this equation:

Calculated Osmolality = 2(Na) + Glucose + Urea

May also see the following equation used:

1.86(Na) + Glucose + Urea + 9

28
Q

What is the osmolal gap and its reference range?

A

Osmolal gap indirectly indicates the presence of osmotically active substances other than sodium, urea, or glucose by calculating the difference between the measured value and the calculated estimated value using this equation:

Osmo Gap = Measured Osmolality - Calculated Osmolality

Reference Range: -10 to 10 mOsm/kg

29
Q

Describe the testing principle for sodium, potassium and chloride using the Cobas c311 (Lab5)?

A

The Cobas c311 uses a ion-selective electrode (ISE) method which has:

  • A special membrane where electrical potential is measured for specific ions in patient samples.
  • The patient’s sample is in contact with the selective membrane in the electrode and an internal filing solution (contains a fixed ion concentration).
  • The potential difference is measured across the selective membrane (test side vs internal filing).
30
Q

What does the Nernst equation calculate and describe mathematically?

A

The Nernst equation describes the action of the ISE mathematically and calculations the electrode EMF (or voltage across the membrane).

EMF = voltage, electromotive force.

31
Q

How much does the Cobas c311 dilute the sample and what is this referred to as?

A

The sample is diluted 1:31 prior to measurement by the Cobas c311.

This is referred to as an “Indirect” ISE measurement.

32
Q

What samples interferences impact the results with the diluted sample the Cobas c311 uses and why?

A

Samples that are hyperlipidemic or hyperproteinemia (high concentrations of lipids and proteins - solid elements within aqueous sample) will result in a displacement of electrolytes to the indirect ISE.

Result –> falsely lowered electrolyte result
(most notably sodium, Na)

33
Q

What principle of measurement does the Vitros 350 use for measuring sodium, potassium, and chloride electrolytes?

A

The Vitros 350 uses potentiometry (instead of reflectance spectrophotometry).

34
Q

Describe how the Vitros single use slides work to measure electrolytes?

A
  1. Each single use slide consists of two ion-selective electrodes (ISE), a reference and measuring electrode.
  2. 10 μL of patient sample and 10 μL of VITROS Reference Fluid are added to separate halves of the slide.
  3. Both fluids will migrate towards the paper bridge in the center of the slide. A stable liquid junction is formed connecting the reference electrode to the sample indicator electrode.
  4. Each electrode produces an electrical potential in response to the activity of the ions applied to it. The potential difference between the two electrodes is proportional to the ion concentration in the sample. This is referred to as a direct ISE potentiometry system.
35
Q

What is the benefit of the Vitros 350 use of direct ISE potentiometry measurement system?

A

The benefit of their system is that a new electrode is used for every measurement.

Now worries about protein buildup and electrode maintenance.

36
Q

What are the layers of the Vitros 350 slide technology?

A

From top to bottom (based on figure in lab instructions):

  1. Upper slide mount
  2. Paper bridge
  3. Ion-selective membrane (Methyl monensin)
  4. Reference layer (NaCl, buffer at pH 5.6)
  5. Silver, silver chloride layer
  6. Support layer
  7. Lower slide mount.
37
Q

What electrolytes can the iSTAT CHEM8+ cartridge provide results for?

A 
Sodium
    Potassium
    Chloride
    Total Carbon Dioxide
    Anion Gap (calculated)
    Ionized Calcium
    Glucose
    Urea
    Creatinine
    Hematocrit
    Hemoglobin
38
Q

What electrochemistry technique is used to measure Sodium, potassium, chloride, ionized calcium, and urea on the iSTAT?

A

Direct ion-selective electrode potentiometry.

The concentration of ion is related to the potential through the Nernst equation.

39
Q

What electrolytes are measured amperometrically on the iSTAT via CHEM8+?

A

Glucose and creatinine

40
Q

How is Total Carbon dioxide determined on the iSTAT / CHEM8+?

A

Total carbon dioxide is calibrated to the reference method based on the Henderson-Hasselbalch equation

41
Q

How are hematocrit, hemoglobin and anion gap determined with the iSTAT/CHEM8+?

A

Hematocrit is measured using conductometry

Hemoglobin and the anion gap are both calculated from the other values obtained.

42
Q

What pre-analytical variables need to be considered when measuring blood gases?

A

Pre-analytical variables that need to be considered for blood gas measurements are:

  1. Ensure sample does not contain air bubbles.
  2. Sample is not exposed to air.
  3. Sample is not clotted.
  4. Correct anticoagulant is used.
  5. Vacuum tube is completely filled.
  6. No evidence of hemolysis.
  7. Properly labeled (venous or arterial sample with correct patient ID).
  8. Testing is done immediately to reduce effects of cellular metabolism.
43
Q

What type of samples can be run on the white G3+ cartridges for blood gas analysis on the iSTAT?

A

Arterial, venous, and capillary samples can be run on white G3+ cartridges for blood gas analysis on the iSTAT.

44
Q

For venous samples what kind of blood collection tubes can be used for blood gas analysis? And for capillary samples?

A
  1. For venous samples, collect a full lithium or sodium heparin tube.
  2. For capillary samples, apply blood drop directly to cartridge or collect in a plain or lithium heparin capillary collection tube. The first drop of blood (containing excess tissue fluid) must be wiped away prior to collection.
45
Q

What components does a blood gas analysis analyze on the iSTAT with the G3+ cartridge?

A

pH, pO2, pCO2

iSTAT also calculates the following values:

TCO2 (total carbon dioxide), HCO3- (bicarbonate), Base excess, and sO2.

46
Q

What is the normal pH range?

A

Normal pH is between 7.35 and 7.45

47
Q

What happens to pH if CO2 is increased in the blood and the resulting condition? Similarly, what if CO2 is decreased?

A

↑ amounts of CO2 and other acids causes pH to ↓ resulting in acidosis.
↓ amounts of CO2 or ↑ bases (HCO3-) causes pH to ↑ resulting in alkalosis

48
Q

What does total carbon dioxide exist as in the body (i.e. its several states)?

A

TCO2 - total carbon dioxide as it exists in several states (bicarbonate + carbonic acid + CO2 associated with proteins)

49
Q

What is the main form of CO2 in the body? How can it be calculated from measured parameters?

A

HCO3- - bicarbonate is the main form of CO2 in the body. It can be calculated from the pH and pCO2 using the Henderson-Hasselbalch equation. It is used as an indicator to the buffering capacity of the blood.

50
Q

What is BE (Base Excess)? What are the interpretations of its value?

A

Base excess (BE) - a calculated number that represents a sum total of the metabolic buffering agents (anions) in the blood. These anions include hemoglobin, proteins, phosphates, and HCO3- (bicarbonate, which is the dominant anion).

A positive value indicates an excess of bicarbonate suggesting metabolic alkalosis
A negative value indicates a deficit of bicarbonate suggesting metabolic acidosis
51
Q

What is sO2?

A

sO2 - percentage of hemoglobin that is carrying oxygen.

52
Q

What type of measuring system does the iSTAT use to measure pH and pCO2?

A

Ion-Selective Electrode (Potentiometry)

Concentrations are calculated from the measured potential through the Nernst equation.

53
Q

How does the iSTAT measure pO2?

A

Amperometrically.

The oxygen sensor is similar to a conventional Clark electrode.

Oxygen permeates through a gas permeable membrane from the blood sample into an internal electrolyte solution where it is reduced at the cathode. The oxygen reduction current is proportional to the dissolved oxygen concentration.

54
Q

What does the iSTAT do every test cycle automatically before measuring the sample?

A
  1. Cartridge makes electrical contact –> identifying the cartridge type.
  2. Calibration is automatically performed as part of the test cycle on every single cartridge. The calibration fluid (containing known concentrations of each analyte) in the sealed foil pack of the cartridge is forced out and over the sensors.
  3. Barometric pressure is measured then sensors are heated to 37°C. The electrical signals generated by the calibration fluid at the sensors are measured.
55
Q

After calibration is done, then what does the iSTAT do to measure blood gases?

A

The sample then displaces the calibration fluid, allowing the patient sample to generate electrical signals that are measured by the sensors. A comparison is made between the calibration and sample. Results are calculated and displayed to the operator.

56
Q

What happens if calibration fails on the iSTAT?

A

If calibration fails, patient results will not be displayed and the sample will need to be reanalyzed with a new cartridge.

57
Q

What medication(s) affect taking samples for PSA and what is the action to take a good sample in such cases?

A

PSA samples should not be collected from patients taking high doses of biotin (>5 mg/day) until 8 hours has lapsed as high levels of biotin interfere with the assay.

58
Q

Normally the prostate gland produces very little PSA, under what pathological conditions do circulating levels of PSA increase?

A

Increases in prostate glandular size.
Tissue damage
Prostatitis
Prostate Cancer, etc.

59
Q

What are the PSA reference range for males?

A

< or = 49 years: < 2.5 ug/L
50-59 years: < 3.5 ug/L
60-69 years: < 4.5 ug/L
> or = 70 years: < 6.5 ug/L

60
Q

Why do you wait 3 days after the last sample collection to develop results for the Fecal Occult Test? (Hemoccult Sensa)?

A

Prevents activity from interfering substances.

61
Q

What are reasons for false positives for the Hemoccult Sensa (FOBT)?

A

False Positives:
1. Consumption of red meat
2. Taking aspirin greater than 325 mg/day
3, Excess intake of alcohol and corticosteroids.

62
Q

What are reasons for false negatives for the Hemoccult Sensa (FOBT)?

A

False Negatives:

  1. Consumption of > 250 mg/day of Vit C
  2. Eating excessive amounts of citrus fruits and juices.

Clinical Chemistry 2 (13 decks)

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