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Clinical Biochem > Non-Protein Biomarkers > Flashcards

Non-Protein Biomarkers Flashcards

1
Q

What is the renin-angiotensin-aldosterone system

A

a mechanism for regulating body water and sodium content

the juxtaglomerular cells of the kidney release renin into the plasma in response to hypotension or decrease in sodium concentration

renin catalyzes the conversion of circulating angiotensinogen to angiotensin I which is converted to angiotensin II as it passes through the lungs. Angiotensin II acts on the adrenal cortex to stimulate the release of aldosterone which acts on the kidney to promote sodium reabsorption, potassium excretion and water retention

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2
Q

What is antidiuretic hormone

A

synthesized and stored in the hypothalamus

release of ADH is stimulated by osmotic and barometric receptors in response to increased plasma osmolality and decreased blood volume

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3
Q

What is ammonia

A

produced in the liver by the deamination of proteins. Ammonia is produced in the intestine by bacterial and endogenous enzymes. Renal tubular cells can produce ammonia from glutamine and other amino acids

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4
Q

What is the clinical significance of ammonia

A

plasma levels of ammonia are increased in instances of liver and kidney disease and the central nervous system disorder Reyes syndrome

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5
Q

What are interferences with ammonia

A

RBC contain ammonia, hemolyzed samples should not be used

cigarette smoke and ethanol significantly increases ammonia concentrations

prolonged venous occlusion and fist clenching increase ammonia

ammonium heparin anticoagulant and delayed handling increase ammonia

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6
Q

What is urea

A

produced in the liver from ammonia, freely filtered but 40-50% is reabsorbed in the proximal tubules

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7
Q

What is the clinical significance of urea

A

increased urea is associated with increased protein deamination due to increased dietary intake and increased protein catabolism from tissue breakdown and GI bleeds

in severe liver disease and individuals with low protein intake urea protein decreases

not a good indicator of renal function

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8
Q

What are interferences with urea

A

sodium fluoride containing anticoagulant inhibits urease

ammonium heparin tubes and endogenous ammonia can be a positive interferent with the second step in the reaction

RBC contain ammonia, therefore hemolysis is a positive interferent

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9
Q

What is uric acid

A

formed from the oxidation of purine bases, is freely filtered and some is reabsorbed in the proximal tubule and the distal tubule excretes uric acid into the urine

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10
Q

What is the clinical significance of uric acid

A

hyperuricemia may be observed in chronic renal failure due to decreased excretion but can also be associated with thiazide diuretics, hypertension and metabolic syndrome

increased production of uric acid is associated with chemotherapy treatment of leukemia, tumor lysis syndrome and diets rich in nucleoproteins

allopurinol is a drug administered to patients undergoing chemotherapy to decrease their circulating uric acid levels to prevent gout and kidney stones which are associated with high concentrations of uric acid

hypouricemia is associated with a decrease in the liver enzymes required for depurination

fanconi syndrome affects the proximal tubules which causes the loss if uric acid in urine causing hypouricemia

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11
Q

What are the interferences for uric acid

A

anticoagulants using sodium fluoride should not be used

bilirubin and ascorbate can interfere with the uricase reaction

bilirubin may falsely decrease results in peroxidase catalyzed reactions

hemolysis may cause decreased results

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12
Q

What is creatinine

A

formed spontaneously in skeletal muscle from creatine and by the enzymatic action of creatine kinase

freely filtered and a small amount is secreted by the renal tubules into urine

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13
Q

What is the clinical significance of creatinine

A

used to estimate glomerular filtration rate, a test of glomerular function

increased concentrations can be caused by any disorder that decreases GFR it can also be transiently increased by diet

decreased concentrations can occur when there is an inadequate conversion from creatine

measured by the Jaffe kinetic reaction

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14
Q

What are interferences for creatinine

A

ketones, ascorbate, cephalosporin, glucose and proteins produce Jaffe like chromogen and cause spectral interference

bilirubin and hemoglobin are negative interferents

lipemia may introduce error

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15
Q

What are the test conditions for creatinine clearance testing

A

a blood specimen must be drawn within 72 hours of either the start or finish time of the urine collection

patients height and weight must be recorded

a 24 hour urine must be collected and refrigerated through out the collection period

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16
Q

What is the formula for creatinine clearance

A

(UV/P)x(1.73/SA)

U = urine concentration of creatinine
P = plasma concentration of creatinine
V = volume of urine in a unit of time (mL/s)
SA = surface area of the patient

there are 86400 seconds in 24 hours

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17
Q

What is the reference interval for creatinine clearance

A

1.30-2.30 mL/sec/1.73m^2

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18
Q

Why does the creatinine clearance test overestimate the GFR

A

because approximately 10% of creatinine in urine is the result of tubular secretion

19
Q

What are the sources of error in the creatinine clearance test

A

pre-analytical errors due to patient compliance with timing, collection, and storage of urine

20
Q

What causes a decrease of creatinine clearance

A

renal disease and heart disease

21
Q

What is the estimated GFR

A

equations can be used to estimate GFR without needing a urine collection

22
Q

When will estimates of GFR not be reliable

A

acute kidney injury, unusually high or low muscle mass, if the patient is on medication that interferes with the tubular secretion of creatinine

23
Q

What does the presence of albumin in the urine indicate

A

damage to the glomeruli and basement membranes such as chronic kidney disease as seen in diabetic nephropathy

24
Q

What does proteinuria due to low molecular weight globulins indicate

A

tubular damage

25
Q

What is microalbuminuria

A

albumin excretion above the normal range but below the level of detection for total protien

26
Q

What is the albumin creatinine ratio used for

A

used to overcome urinary variations that are due to albumin concentration of hydration

the spot urine is preferred over the 24 hour collection due to patient compliance

27
Q

How is screening done for kidney disease

A

urine reagent strips are used, if two screen three months apart are positive then the ACR is used as follow up

28
Q

What is B-microglobulin

A

a small peptide that is part of the major histocompatibility complex

it is present on the surface of cells and is found in low but usually constant concentrations in plasma

it is freely and completely filtered by the glomerulus and then is reabsorbed and catabolized by the PCT cells

food indicator of GFR in normal patients

29
Q

When is B-microglobulin increased

A

certain inflammatory diseases, renal failure and malignancies

30
Q

When is blood and urine B-microglobulin used

A

to assess the integrity of the renal tubules particularly in renal transplant patients and those exposed to heavy metals

31
Q

What is the characterization of acute kidney injury

A

a rapid reduction in kidney function that may present as oliguria or increased plasma creatinine

risk factors include increased age, diabetes, chronic kidney disease, heart disease and administration of nephrotoxic drugs

32
Q

What is prerenal AKI

A

caused by factors affecting the blood supply to the kidney

commonly caused by cardiac failure and hypoglycemia due to burns, hemorrhage, vomiting, diarrhea and sepsis

33
Q

What is renal AKI

A

the result of vascular, glomerular or interstitial damage

can be the result of aminoglycosides, nonsteroidal anti-inflammatory drugs, myoglobinuria or heavy metal poisoning

34
Q

What is post renal AKI

A

the result of an obstruction in the flow of urine after it leaves the kidney

can be caused by prostatic enlargement, renal stones, fibrosis, or neoplasms of the urinary tract

34
Q

What is CKD

A

the result of a progressive loss of renal function

the loss of renal function is irreversible

the number of functioning nephrons is decreased, urine tends to have a fixed specific gravity, isosthenuria indicates a lack of concentrating ability

35
Q

How is CKD defined and staged

A

using estimated glomerular filtration rate, eGFR and urinary albumin/creatinine ratio

36
Q

What is the primary cause of CKD

A

diabetes mellitus

37
Q

What are other causes of CKD

A

glomerular nephritis, inherited disorders, infection and systemic diseases

38
Q

What is the reference range for eGFR

A

<60 mL/min/1.73m^2

39
Q

What is the reference range for plasma ammonia

A

<35 umol/L
critical - >199 umol/L

40
Q

What is the reference range for creatinine

A

females - 40-100 umol/L
males - 50-120 umol/L

41
Q

What is the reference range for urea

A

2.5-8.0 mmol/L

42
Q

What is the reference range for uric acid

A

females - 150-400 umol/L
males - 200-500 umol/L

Clinical Biochem (8 decks)

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