American Association for Clinical Chemistry
Better health through laboratory medicine
December 2008 Clinical Laboratory News: Diagnostic Profiles

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December 2008: Volume 34, Number 12

  Survey Shows Labs Struggle with Critical Value Reporting

Being able to report critical values for outpatient-related tests is the single greatest obstacle faced by laboratorians in accomplishing this important patient safety function, according to a survey of more than 350 hospitals and hospital systems (Arch Pathol Lab Med 2008;132:1666–1671). Three-quarters of respondents reported experiencing difficulty in getting outpatient providers to return calls or pages. New strategies for making contact with the covering provider are needed in this population particularly, because the patients are not necessarily easy to reach or in close proximity to medical services. Authors of the study also report how some labs have investigated ways to reduce false-positive results for outpatient values. For example, a case study at one institution found that plasma potassium drawn at the same time and being placed in ice with HbA1c samples had a high number of critical values, which on resampling were determined to be within normal limits. The lab subsequently eliminated the send-on-ice requirement and experienced a 20% to 40% drop in potassium critical values. Researchers also found considerable variability in other aspects of critical value reporting. For instance, about 18% of labs indicated they use customer service centers to handle critical value callbacks, but the majority still rely on the technologist who performed the test to do so. Approximately 22% reported not having compared their critical value lists with national norms, while 24% indicated they have not measured the time between a critical result becoming available and being relayed to the responsible clinician. While the majority of labs used a combination of calling the ordering location, the patient’s physician, or a nurse or nurse manager, 8.6% reported using wireless technology, such as pagers, to notify the caregiver. The authors believe the survey findings fill a void in the literature about improving critical value responses at a time when critical values have become more prominent in patient safety initiatives.

PSA Assay Standardization Bias Could Affect Clinical Decision-Making

The two most common PSA assays yield discordant results and could have negative consequences for clinical decision-making, according to findings from a recent prospective study (Journal of Urology 2008; 180:1959–1963). The findings are of particular import because many physicians and patients are not aware of the assay used for any individual PSA test. Researchers tested 1,916 samples using both the Hybritech Access assay with Hybritech standardization and the ADVIA Centaur assay with WHO 90:10 standardization, the two most common commercial PSA assays. They found 17% and 38% differences in the median and mean PSAs, respectively, with the Centaur assay lower in both instances. Using a PSA threshold of 2.5 ng/mL, 5% of subjects would have been recommended for a prostate biopsy with one assay but not the other. The study also revealed that if the tests were used sequentially, differences in the assays could either over- or understate PSA velocity, a key factor in predicting prognosis. In fact, 26%, 14.5%, and 4.5% of subjects had a potentially misleading PSA difference between the tests of greater than 0.4, 0.75, and 2.0 ng/mL, respectively. The researchers concluded that there is a need for greater awareness of PSA assay standardization discrepancies and called for manufacturers and clinical labs to provide information about which assay their test is based on, and for lab reports to clearly state the assay manufacturer.


CRP, Troponin Predict Significant Increase in Risk of Death after AMI  

Patients with CRP and troponin positivity have a two times greater risk of dying within 28 days after an AMI, and both troponin and CRP were independent predictors of 28-day case fatalities, according to a recent prospective study (Am J Cardiol 2008; 1125–2230). The study involved 1,646 patients who had experienced fatal coronary events or non-fatal AMIs and were consecutively enrolled in the WHO Monitoring Trends and Determinants on Cardiovascular Diseases (MONICA) project. In investigating the prognostic role of CRP and troponin for both ST-elevation MI (STEMI) and non-STEMI, researchers found that in patients with STEMI, troponin positivity but not CRP positivity independently predicted 28-day fatality. The situation was reversed in non-STEMI patients: CRP positivity but not troponin positivity predicted 28-day mortality. The latter finding is incongruent with other studies; however, those studies included a significant number of patients with unstable angina only and not increased myocardial necrosis factors, according to the authors. In contrast, this analysis excluded patients with unstable angina and had only a “negligible” number of patients with no increase in myocardial necrosis markers. Researchers called for further studies to determine whether strategies such as immediate adoption of high-dose statins or very early interventional therapies might be beneficial for higher-risk patients identified by increased CRP levels upon hospital admission.

Statin Treatment, PSA Declines Linked

PSA levels declined significantly after initiation of statin treatment, and the reduction was greatest among men with larger decreases in LDL-C, higher statin doses, and higher pre-statin PSA levels, new research shows (J Natl Cancer Inst 2008; 1511–1518). This longitudinal study included 1,214 men who were free of prostatitis and prostate cancer, had not undergone prostate surgery or taken medications known to alter androgen levels, and for whom there was at least one PSA value within 2 years before and at least one PSA value within 1 year after starting statin therapy. Researchers found that after starting a statin, median LDL-C decline was 27.5% and the median PSA decline was 4.1%. Changes in PSA levels were strongly associated with statin dose and changes in LDL-C levels. For every 10% drop in LDL-C after starting a statin, PSA levels declined by 1.64 %. Doses of at least 20 mg simvastatin were associated with a 8.5% greater decrease in PSA than doses less than 20 mg. Researchers conclude that if confirmed through other studies, their findings would justify further investigation into the relationship between statins and PSA, and whether statins directly influence prostate biology. They also caution that additional study is needed to assess the influence statin-mediated PSA reductions could have on cancer detection protocols.