Clinical Chemistry, Toxicology, Drug Testing 20%

Question 1

BUN = 1/GFR

Answer 1

Normal BUN:Creatinine ratio = 10:1 to 20:1

Abnormal:
>20:1 = Prerenal low perfusion
10:1 to 20:1 = Renal

Question 2

Decreased insulin = increased potassium

Answer 2

because whenever glucose is transported into cells under the
influence of insulin, it is accompanied by potassium

Question 3

In patients with hyperglycemia, for each mmol/L rise in glucose (above a plasma glucose level of 5.6
mmol/L), what happends to plasma Na?

Answer 3

In patients with hyperglycemia,
for each mmol/L rise in glucose

(above a plasma glucose level of 5.6
mmol/L),

plasma Na decreases by 0.288 mmol/L

Question 4

Nonprotein Nitrogenous compounds

Answer 4

Major Components of the Nonprotein Nitrogenous compounds Fraction

Compound Approximate plasma concentration (% of total NPN)
Urea 45
Amino Acid 20
Uric Acid 20
Creatinine 5
Creatine 1-2
Ammonia 0.2

Question 5

The concentration of a substance is directly proportional to the amount of light absorbed or
inversely proportional to the logarithm of transmitted light

Answer 5

Beer-Lambert’s Law

Question 7

Method of Cockcroft and Gault (1976) for Estimating Creatinine Clearance
Based on serum creatinine with correction for age & weight

Answer 7

for males in mL/min = (140 - (age in years)) * (body weight in kg)/
(72 * (serum creatinine in mg/dL)

for females in mL/min = (0.85) * (140 - (age in years)) * (body weight in kg) / (72 * (serum creatinine in mg/dL)
OR
= (140 - (age in years)) * (body weight in kg)/(85 * (serum creatinine in mg/dL)

*Body weight is the adjusted body mass (use ideal body weight if current body weight exceeds the ideal body weight, else use the current body weight)

*a serum creatinine of 1 mg/dL should be used if the serum creatinine is under 1 mg/dL.

*the calculated clearance should be reduced in patients with spinal cord injuries (20% if paraplegic; 40% if
quadraplegic)

Limitations: This applies for adults 20-100 years of age.

Question 8

Renal Failure Index (RFI)
Specimens should be obtained before onset of treatment.
Renal failure Index (RFI) in mEq/L = Urine Na in mEq/L x Plasma Creatinine in mg/dL/
Urine Creatinine in mg/dL

Answer 8

Interpretation
* RFI <= 1: prerenal azotemia
* RFI =1-3: less definitive but usually indicates tubular necrosis
* RFI >= 3: acute tubular necrosis