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Updated December 28, 2009

How is it possible to have PaO2 measurements greater than 800 mm Hg? Our blood gas analyzer (Nova Biomedical’s Critical Care Xpress) operates at atmospheric pressure with a linear range of zero to 800 mm Hg. We see cardiac bypass patients who are cooled to temperatures of 16° to 21°C presenting with PaO2 values of 750 to 850 mm Hg. Results greater than the measurement range are reported as that.
(November 2009)

We recently had several physicians question our high-density lipoprotein values, which changed from one testing date to another. For example, on March 7, 2008 a patient had an HDL of 26 mg/dL. The patient was retested June 6, 2008 and his HDL was 33 mg/dL. The affiliated hospital repeated several tests, and we correlated very well. These physicians believe that since HDL is genetic, the results should not vary that much. I have looked in the Tietz Textbook of Clinical Chemistry, and it appears there can be wide variation. Can you clarify this so I can give our physicians the correct information?
(September 2009)

With our new blood gas analyzers, we sometimes have problems reporting values when we have patients with high methemoglobins. The manufacturer assures us that, because our machine is so sensitive and reads at 520 wavelengths, the analyzer doesn’t know if it is detecting methemoglobin or something else. So we don’t get a result we can report. How do we know whether to treat the patient for high methemoglobin? What can we do?
(April 2009)

Is it necessary to analyze the fasting glucose before giving a patient glucola for a glucose tolerance test, or is it acceptable to draw the fasting glucose and give the glucola right away?
(August 2008)

When you obtain a triglyceride result above 1,000 mg/dL by colorimetric determination and the cholesterol result is below 300 mg/dL, is it correct to report very-low-density lipoprotein, or VLDL, calculation?
(July 2008)

There is a lot of information about how to freeze serum and plasma specimens, but I cannot find anything on how to thaw them properly. Can you help?
(March 2008)

Is literature available regarding testing blood drawn from an intraosseous line?
(July 2007)

As our laboratory tries to strengthen its specimen rejection policy, we are stuck on the issue of hemolysis in blood samples. At what level of hemolysis, based on a colored reference chart with examples of hemolysis levels, should all specimens be rejected? Should this threshold be reduced for potassium and other analytes?
(May 2007)

Have studies been done on centrifuged serum separator tubes, or SSTs, that are sent through a pneumatic tube system to a main laboratory? Should the blood samples be recentrifuged?
(February 2007)

What are the best tests to assess the risk of developing acute renal failure from accumulating myoglobin in the kidney following rhabdomyolysis? This is a good question, to which there is no definitive answer.
(November 2006)

Is it critical that sodium fluoride tubes be used to collect specimens for lactate?
(May 2006)

We perform 24-hour urine creatinines in-house. A resident physician, who is our chief of nephrology, director of dialysis, and a board-certified nephrologist, requested we set up a six-hour urine creatinine panel because the test helps him manage his acute renal failure patients.
(March 2006)

Are finger-sticks or capillary blood-draw tubes appropriate for all chemistries or for general chemistry, therapeutic drug monitoring, or oncology? Have the manufacturers or literature noted any validations?
(February 2006)

Why are there so many published equations for calculating osmolality and is one equation best? Should the laboratory provide a calculated osmolality in addition to the measured value?
(January 2006)

Does serum carbon dioxide content decrease when the assay tube sits unstoppered?
(April 2005)

Should vitamin B12 and folate still be requested simultaneously?
(February 2004)

How should we address a discrepancy between the calculated low-density lipoprotein cholesterol and the directly determined LDL?
(November 2003)

What product can be used to perform calibration verification for methemoglobin?
(August 2003)

What is the best alternative to a sweat chloride test we can offer our concerned pediatricians and obstetricians?
(May 2003)

Are precalibrated assays from the manufacturer exempt from the requirement to recalibrate at least every six months?
(May 2003)

Should blood ammonia determinations be performed using plasma from venous blood or from arterial blood?
(September 2002)

What are the internal and external variables that can retain abnormal values for triglycerides in light of Zocor or Lipitor (20 mg or 10 mg) prescribed treatment?
(July 2002)

What guidance is available for interpreting direct LDL measurements?
(July 2002)

How can an albumin/creatinine ratio on a random specimen (urine) be reported in units of number of grams creatinine when urinary total protein and creatinine are generally mg/dL?
(June 2002)

Can you comment or send me references on the validity of determining a lipid profile during the first 24 hours of myocardial infarction?
(May 2002)