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Flashcards in Laboratory Medicine Deck (15)
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What may cause a false lab report of hyperkalemia?

Hemolysis of the blood sample. Repeat the test if a high value does not make sense (e.g., high level with no electrocardiogram [ECG] changes or symptoms).


What can cause a “false” hyponatremia (pseudohyponatremia)?

hyperglycemia, hyperproteinemia, or hyperlipidemia.

The hyponatremia resolves with correction of the glucose, lipid, or protein levels.


What may result from rapid correction of hyponatremia?

Central pontine myelinolysis

For this reason you should generally not give hypertonic saline to correct hyponatremia except in severe or symptomatic cases, and then it should be given in limited quantities.


What effect do serum acidosis and serum alkalosis have on potassium
and calcium levels?

Alkalosis: hypokalemia and symptoms of hypocalcemia (perioral numbness, tetany)

Acidosis: hyperkalemia.

Correction of acid-base status will correct the potassium and calcium derangements.


Other than pancreatic disease, what else can cause elevated levels of amylase and lipase?

Damage of the salivary glands or bowel, renal failure, and ruptured tubal pregnancy may cause amylase and lipase elevations. Elevation of both amylase and lipase in the same patient, however, is usually caused by pancreatitis.

The boards may try to trick you with an isolated elevation of amylase.


Which diseases can cause elevated levels of alkaline phosphatase?

What laboratory test is used to distinguish among these diseases?

biliary disease, bone disease, or pregnancy (placenta produces AlkPhos)

If the elevation is due to biliary disease, gamma- glutamyltranspeptidase (GGT) and/or 5′-nucleotidase (5′-NT) also should be elevated; both values are normal in bone disease and pregnancy.


True or false: Hypothyroidism can cause elevated cholesterol.

True. Thyroid hormone replacement corrects the elevated cholesterol.


Injury to what organ (other than the heart) causes elevated levels of creatine kinase (CK)?

Muscle. Watch for trauma, rhabdomyolysis, HMG-CoA reductase inhibitors (which can cause muscle damage), and burns.


What is the relationship of low calcium and potassium levels to low levels of magnesium?

HypoK and/or hypoCa may be caused by hypoMg. If hypoMg is present, it is often impossible to correct the hypoK or hypoCa until you correct the hypoMg. If a patient has hypoK that does not correct with K supplements, check the Mg level.


Which two electrolytes are classically depleted in the setting of diabetic ketoacidosis or diabetic hyperosmolar, hyperglycemic state?

K and phosphorus


What does a blood urea nitrogen (BUN)-to-creatinine ratio greater than 15 or 20 generally imply?



What disease classically causes a false-positive result on the rapid plasma reagin (RPR) or venereal disease research laboratory (VDRL) syphilis test?

Systemic lupus erythematosus (SLE). A false-positive result on the RPR or VDRL test is actually one of the diagnostic criteria for SLE.


Define isosthenuria. What condition/s does it suggest?

Isosthenuria - inability to concentrate or dilute the urine. The specific gravity of urine and serum is the same - classically 1.010. Isosthenuria is often associated with sickle cell trait or disease.


What does an elevated erythrocyte sedimentation rate mean in pregnancy?

Nothing. This is a normal finding in pregnancy (i.e., it is not a good test to order in a pregnant patient).


True or false: A high-normal level of BUN or creatinine during pregnancy often indicates renal disease.

True - BUN and creatinine are decreased significantly in pregnancy after the first trimester in women with normal renal function.