Kidney Function Tests

Question 1

Creatinine

Answer 1

Produced enzymatically by creatinine phosphokinase from creatine, which links with ATP to produce ADP and energy.

Question 2

Disadvantages Of Creatinine Clearance

Answer 2

• Some is secreted by the tubules
• Chromogens in plasma interfere
• Medications including gentamicin and cephalosporins may inhibit tubular secretion
• Bacteria will break down creatinine overtime
• A meat heavy diet will influence plasma results
• Patients suffering from muscle wasting diseases have unreliable results
• Results depend upon completeness of 24 hour collection
• Must be corrected for body surface area

Question 3

Cystatin C

Answer 3

Small protein produced at a constant rate by all nucleated cells, as measured by immunoassays, levels are independent of muscle mass

Question 4

Beta-2 microglobulin

Answer 4

Dissociates from HLA antigens at a constant rate and is rapidly removed from plasma by glomerular filtration, it is found by enzyme immunoassay.

Question 5

GFR

Answer 5

Used to determine the extent of nephron damage in known cases of renal disease and to monitor the effectiveness of treatment

Question 6

Specific Gravity Definition, Interferences, Reagent Strip Methodology

Answer 6

• Most useful as a screening procedure, controlled intake procedures include overnight fluid deprivation for 12 hours followed by a urine sample collection
• Influenced by the number and density of the particles, unlike Osmolality
• Specific gravity will be altered in patients who are receiving dextran or other plasma expanders, reagent strips (change in PKA of a polyelectrolyte in an alkaline medium) or osmometry is better to use because they’re not affected by these substances

Question 7

Refractometry Definition, Advantages, Corrections

Answer 7

Determines the concentration of dissolved particles by measuring refractive index, the refractive index is a comparison of the velocity of light and air with a velocity of light in a solution

Uses a small volume of specimen, the corrections are needed for glucose and protein by subtracting .003 for each gram of protein and .004 for each gram of glucose

Question 8

Osmometer Freezing Point Method

Answer 8

Determine the freezing point of a solution by supercooling a sample to 27°C, it is then vibrated to produce crystallization of water, heat of fusion from crystallization temporarily raises the temperature to it’s freezing point.

Question 9

Vapor Pressure Osmometer Procedure

Answer 9

1. Sample is absorbency onto filter paper and placed in a sealed chamber with temperature sensitive thermocouplers
2. The sample evaporates and forms a vapor
3. When the temperature is lowered water condenses in the chamber and on the thermocoupler
4. The heat of condensation raises the temperature to the dewpoint temperature which is proportional to the vapor pressure.

Question 10

Factors Affecting Osmolarity

Answer 10

Osmolarity readings are affected by lipemia, lactic acid, and volatile substances such as ethanol

Question 11

PAH Defintition, Calculation

Answer 11

Non-toxic substance is loosely binds to plasma proteins, which permits it’s complete removal as blood passes through the peritubular capillaries

The volume of plasma flowing to the kidneys determines the amount of PAH excreted in the urine

C(PAH)(mL/min)=(U(mg/dL) PAH x V(mL/min urine))/P(mg/dL PAH)