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The Essence: The Best of October 2019

By Anne-Margaret Olsson posted 28 days ago

The Artery is your community for finding solutions to your day-to-day clinical chemistry questions. Last month, several answers were found to questions ranging from “How many IO-PTHs do others run at their hospitals?” to “What instruments do labs use to report the pH on cord blood specimens?” Read on for our editor’s picks of the best discussions on the Artery in October.

Intraoperative PTH Volume?
Initiated by @Charles Beavers, MD

How many IO-PTHs do others run at their hospitals, and at what volume does it make sense to have a stat lab for this test? Other institutes run anywhere from 1-2 per week to 1-2 per day. Labs in the 1-2 per week range run their IO-PTHs in the main lab, while labs close to the 1-2 per day range tend to run their IO-PTHs either on a mobile lab cart (with the main lab serving as the backup) or in a stat lab near the OR.

Umbilical Cord pH
Initiated by @Pam Norman, ASMT

What instruments do labs use to report the pH on cord blood specimens and what literature do they use to support this testing? Respondents use blood gas analyzers for this type of testing and they also recommended several different sources for reference ranges. These included Tietz’s “Clinical Guide to Laboratory Tests,” as well as a journal paper that provides reference values for umbilical cord arterial and venous pH in preterm and term newborns.

More Sensitive Waived Urine Pregnancy Test
Initiated by @Qingli Wu, PhD

A lab is wondering if there are any waived urine pregnancy tests that don’t have high false negative rates, because their physicians prefer a quicker turnaround time than what serum hCG can provide. Respondents indicated that serum hCG really is the best test for lowering false negatives, though, and recommended improving turnaround time by 1) establishing autoverification rules in middleware, 2) setting up a preliminary report so that initial elevated results are reported as positive, rather than held until the final result is available after dilution, and 3) optimizing tube handling so that hCG is sampled first on the automated analyzer.

Correction of Sodium Results With Hyperglycemia
Initiated by @Pam Norman, ASMT

One institution’s pharmacy is requesting corrected sodium levels for hyperglycemia due to the anion gap calculation. Are any labs doing this? The majority of respondents don’t do this and don’t recommend it. In hyperglycemic pseudohyponatremia, the measured sodium concentration is accurate, but doesn’t reflect total body sodium because of the hyperosmotic effect of the high glucose concentration. Correcting sodium therefore only helps to predict whether a patient is truly sodium deficient due to renal dysregulation, and it shouldn’t be used to “correct” the anion gap.