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dms test 2 > Osmolality, PSA, RF, Uric Acid > Flashcards

Osmolality, PSA, RF, Uric Acid Flashcards

1
Q

What is Osmolality used for? Normal and critical values?

A

Used to gain information about fluid status and electrolyte imbalance.

Also assists in evaluating diseases involving ADH.

Normal: 285-295 mOsm/kg H2O

Critical values: < 265 mOsm/kg H2O, > 320 mOsm/kg H2O

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2
Q

What does Osmolality measure?

What happens when osmolality increases or decreases? (general)

A

Measures the concentration of dissolved particles in the blood.

As free water in blood increases or the amount of particles decreases, osmolality decreases. (Overhydration)

As free water in blood decreases or the amount of particles increases, osmolality increases. (Dehydration)

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3
Q

What is the feedback mechanism to control Osmolality?

A

Increased osmolality stimulates secretion of ADH to increase water reabsorption in the kidneys to make more concentrated urine and less concentrated serum.

Decreased osmolality suppresses ADH secretion to decrease water reabsorption and cause large amounts of dilute urine

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4
Q

What does an Osmolality value > 385 associated with?

What about 400-420?

> 420?

A

Values > 385 are associated with stupor in patients with hyperglycemia

Values 400-420 can cause seizures, and values > 420 can be lethal

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5
Q

What causes increased Osmolality Levels?

A

Hypernatremia, hyperglycemia – all cause increased number of particles dissolved in the blood.

Dehydration.

Ingestion of ethanol, methanol, or ethylene glycol – stimulate free water loss from kidneys and excretion in the urine. Also, their byproducts cause an increase in the number of solutes in the blood.

Uremia, renal tubular necrosis, severe pyelonephritis – poor urine concentration leading to free water loss

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6
Q

What causes Decreased Osmolality Levels?

A

Overhydration

Syndrome of inappropriate ADH (SIADH) secretion – can be caused by several illnesses. ADH is inappropriately secreted despite factors that normally inhibit its secretion. This leads to large quantities of water being reabsorbed by the kidneys and serum becoming dilute.

Paraneoplastic syndromes associated with carcinoma (lung, breast, colon) – act as an autonomous ectopic source for secretion of ADH

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7
Q

What is the Osmolar gap?

Normal value?

A

Osmolar gap represents the difference between what the osmolality should be based on calculations of serum sodium, glucose, and BUN (the 3 most important solutes in the blood) and the osmolality as truly measured

Normal is < 10 mOsm/kg H2O

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8
Q

What is suspected to be present in a large Osmolar gap?

A

If the gap is large, solutes such as organic acids (ketones) or unusually high levels of glucose or ethanol byproducts are suspected to be present

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9
Q

How do you calculate the Osmolar Gap?

2 steps

A

1.)
Calculated osmolality =
(2 X [sodium]) + ([glucose]/20) + ([BUN]/3)

2.)
Lab serum osmolality – calculated osmolality = osmolar gap

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10
Q

What are the Interfering Factors for Osmolar Gap?

A

Hemolysis invalidates sodium, glucose, and BUN values.

Sodium concentration may decrease by 1.6 mEq/L for every 100 mg/dL increase in plasma glucose concentration because of an osmotic shift of water into the bloodstream causing a pseudohyponatremia

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11
Q

What cause Increased levels of the Osmolar gap?

A

Decrease in serum water content (severe hyperlipidemia)

Hyperproteinemia – macroglobulinemia and multiple myeloma

Presence of low molecular weight solutes such as ethanol, methanol, ethylene glycol, isopropanol, or mannitol in the blood

Diabetics with hyperglycemia

Chronic renal failure when dialysis is needed

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12
Q

What is the Prostate Surface Antigen (PSA) used for?

Normal values?

A

Used as a screening method for early detection of prostate cancer.

When combined with a rectal exam, nearly 90% of clinically significant cancers can be detected.

Also used to monitor disease after treatment

Doctor Gersten said to not memorize these:
Normal findings: 0-2.5 ng/mL is low, 2.6-10 is slightly to moderately elevated, 10-19.9 is moderately elevated, 20 or more is significantly elevated

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13
Q

What is PSA?

A

PSA is a glycoprotein found in high concentrations in the prostatic lumen.

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14
Q

When should a PSA test be offered for men?

When is it advised against?

A

PSA testing should be offered to men at 50 or older unless they have increased risk factors such as genetic predisposition or African American race when it should be offered between 40 and 50.

Advise against PSA testing to screen for prostate cancer in men 75 or older

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15
Q

What should also be performed with the PSA test?

A

Digital rectal exam should also be performed – combination of the two tests is more sensitive than either one alone.

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16
Q

What causes does the level of PSA indicate?

A

Elevated PSA is associated with prostate cancer.

Levels more than 4 ng/mL have been found in more than 80% of men with prostate cancer.

The higher the levels, the greater the tumor burden (mass of the tumor)

17
Q

What other PSA tests may be performed?

A

Some patients with early prostate cancer will not have elevated PSA, and levels above 4 are not always associated with cancer. Other measures have been proposed:

PSA velocity
Age adjusted PSA
Free vs. attached PSA

18
Q

What is PSA velocity?

A

Change in PSA levels over time.
A sharp rise should raise suspicion of cancer and may indicate a fast growing cancer

PSA velocity > 0.35 ng/mL/year have higher risk of dying from prostate cancer

19
Q

What is Age Adjusted PSA? (Age values)

A

Men < 50 should have a PSA < 2.4, whereas 6.5 is normal in a 70 year old

20
Q

What is Free vs. attached PSA?

A

PSA circulates in free form and bound to protein.

With benign prostate conditions (BPH) there is more free PSA, while cancer produces more bound form

If attached PSA is high but free is not, then there is a greater chance of cancer

21
Q

What are the Interfering factors for PSA?

A

Rectal exams may falsely elevate PSA.

Prostatic manipulation by biopsy or TURP will elevate PSA.

Ejaculation within 24 hours of blood testing may elevate PSA.

Recent UTI or prostatitis may elevate PSA as much as 5X the baseline for up to 6 weeks

22
Q

What causes increased levels of PSA?

A

Prostate cancer
Benign Prostatic Hypertrophy (BPH)
Prostatitis

Because:
Prostate gland tissue and vascular structure are between the lumen and the bloodstream, so when cancer, infection, and benign hypertrophy occur the barriers can be penetrated and PSA is released into the blood stream

23
Q

What is Rheumatoid Factor (RF) useful for? How is it measured? Normal value?

A

Useful in diagnosis of rheumatoid arthritis (RA).

Measured by titer or units/mL
80% of patients with RA have positive RF titers.

A normal value is less than 60 units/mL.

RF is not a useful disease marker as it does not disappear in patients in remission – not helpful in screening for reoccurrences. –> It stays up.

24
Q

What happens in Rheumatoid arthritis (RA)?

A

In RA, abnormal IgG antibodies produced by lymphocytes in the synovial membranes act as antigens, so other IgG and IgM antibodies in the serum react with the antigenic IgG to produce immune complexes.

These complexes activate the complement system and other inflammatory systems to cause joint damage.

The reactive IgM and sometimes IgG and IgA make up rheumatoid factor.

Blood vessels, lungs, nerves, and the heart may also be involved in the autoimmune inflammation

25
Q

What dilutions must be used for a positive test for RA?

A

RF must be found in a dilution of > 1:80 to be positive.

RF found in titers < 1:80 may be due to SLE, scleroderma, and other autoimmune conditions.

A negative RF does not exclude RA.

26
Q

Where can a positive RF test be seen?

A 
Rheumatoid arthritis
SLE
Sjogren syndrome
Tuberculosis
Chronic hepatitis
Infectious mononucleosis
Subacute bacterial endocarditis
27
Q

What is Uric Acid used for? Normal range? Critical?

A

Used in the evaluation of gout or recurrent urinary calculus (kidney stones)

Normal range: Male 4.0-8.5 mg/dL; Female 2.7-7.3 mg/dL
Critical value: > 12 mg/d

28
Q

Where is Uric acid made?

A

Mainly made in the liver – blood level is determined by the rate of synthesis in the liver and the rate of excretion by the kidney.

Uric acid is a nitrogenous compound that is the final breakdown product of purine catabolism.

75% is excreted by the kidney and 25% by the GI tract.

29
Q

Does an elevated uric acid diagnose gout?

A 
NO! 
When elevated (hyperuricemia), the patient may have gout – elevated serum uric acid does not diagnose gout!!!!
It does not show levels in the joints.
30
Q

What is Gout?

A

Gout is a form of arthritis caused by deposition of uric acid crystals in the periarticular tissue.

Soft tissue deposits of uric acid are called tophi

31
Q

How can uric acid form kidney stones?

A

Uric acid can also become supersaturated in the urine and crystallize to form kidney stones.

32
Q

What are Interfering Factors for Uric Acid?

A

Total parenteral nutrition high in protein may cause increased levels.

Drugs causing increased levels include alcohol, caffeine
Drugs causing decreased levels include allopurinol, aspirin (high dose), azathioprine, corticosteroids, probenecid

33
Q

What cause Increased Levels of Uric Acid (Hyperuricemia)?

A

Increased Production of Uric Acid

Decreased Excretion of Uric Acid

34
Q

What causes Increased Production of Uric Acid?

A

Increased ingestion of purines – liver, sweetbreads, kidney, anchovies.

Genetic inborn error in purine metabolism (Enzyme deficiency that stimulates purine metabolism).

Metastatic cancer, multiple myeloma, leukemias, cancer chemotherapy – rapid cell destruction with rapidly growing cancers that have high cell turnover, and especially after chemotherapy for rapidly growing tumors cause cells to lyse and spill nucleic acids into the bloodstream

35
Q

What causes Decreased Excretion of Uric Acid?

A

Idiopathic – most common cause of hyperuricemia . Reduced uric acid clearance in the kidneys. Gout patients excrete less than half the uric acid in their urine as normal persons.

Chronic renal disease.

Acidosis (ketotic [diabetic or starvation] or lactic) – decreased renal tubular secretion of uric acid in the urine. Ketoacids may compete with uric acid for tubular excretion.

Alcoholism – accelerated breakdown of ATP in the liver increases uric acid production

dms test 2 (11 decks)

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