Laboratory Medicine Flashcards
What may cause a false lab report of hyperkalemia?
Hemolysis of the blood sample. Repeat the test if a high value doesn’t make sense (e.g. high level with no EKG changes or symptoms).
What can cause a “false” hyponatremia?
Hyperglycemia, hyperproteinemia, or hyperlipidemia. Resolves with correction of the glucose, lipid, or protein levels.
What may result from rapid correction of hyponatremia?
Brainstem damage (central pontine myelinolysis). Generally do 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 may cause hypokalemia and symptoms of hypocalcemia (perioral numbness, tetany) due to cellular shift, whereas acidosis may cause hyperkalemia by the same mechanism. 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 due to pancreatitis.
Which diseases can cause elevated levels of alkaline phosphatase? What lab test is used to distinguish among these diseases?
Biliary disease, bone disease, or pregnancy (placenta produces alkaline phosphatase).
If elevation is due to biliary disease, gamma-glutamyl-transpeptidase (GGT) and/or 5’-nucleotidase (5’-NT) also should be elevated; both values, however, 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?
Hypokalemia and/or hypocalcemia may be due to hypomagnesemia. If hypomagnesemia is present, it is often impossible to correct the other two until you correct the magnesium. If a patient has hypokalemia that does not correct with potassium supplements, check the magnesium level.
Which two electrolytes are classically depleted in the setting of diabetic ketoacidosis or diabetic hyperosmolar, hyperglycemic state?
Potassium and phosphorus
What does a BUN-to-creatinine ratio greater than 15 or 20 generally imply?
Dehydration
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 on the RPR or VDRL test is actually one of the diagnostic criteria for SLE.
Define isosthenuria. What condition does it suggest?
Inability to concentrate or dilute urine. The specific gravity of urine and serum is the same - classically 1.010. It 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. 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.
