Clinical decision limits as criteria for setting analytical performance specifications for laboratory tests

BACKGROUND

The biological (CV_I), preanalytical (CV_PRE), and analytical variation (CV_A) are inherent to clinical laboratory testing and consequently, interpretation of clinical test results.

METHODS

The sum of the CV_I, CV_PRE, and CV_A, called diagnostic variation (CV_D), was used to derive clinically acceptable analytical performance specifications (CAAPS) for clinical chemistry measurands. The reference change concept was applied to clinically significant differences (CD) between two measurements, with the formula CD = z*√2* CV_D. CD for six measurands were sought from international guidelines. The CAAPS were calculated by subtracting variances of CV_I and CV_PRE from CV_D. Modified formulae were applied to consider statistical power (1-β) and repeated measurements.

RESULTS

The obtained CAAPS were 44.9% for urine albumin, 0.6% for plasma sodium, 22.9% for plasma pancreatic amylase, and 8.0% for plasma creatinine (z = 3, α = 2.5%, 1-β = 85%). For blood HbA_1c and plasma low-density lipoprotein cholesterol, replicate measurements were necessary to reach CAAPS for patient monitoring. The derived CAAPS were compared with analytical performance specifications, APS, based on biological variation.

CONCLUSIONS

The CAAPS models pose a new tool for assessing APS in a clinical laboratory. Their usability depends on the relevance of CD limits, required statistical power and the feasibility of repeated measurements.

Inter-institutional variations regarding Barrett's esophagus diagnosis

BACKGROUND

Barrett's esophagus (BE) is a known precursor for development of esophageal adenocarcinoma and surveillance of affected patients is necessary when cancer progression risk is considered to be high. However, the accuracy of BE diagnosis may not be homogenous among institutions with endoscopy units. We investigated inter-institutional variability by examining the accuracy of endoscopic diagnosis of BE at 4 different hospitals.

METHODS

The accuracy of BE diagnosis at the 4 hospitals was retrospectively reviewed by 6 expert endoscopists, who independently reviewed endoscopic images of approximately 500 consecutive patients examined at each hospital without information regarding the diagnosis by the on-site endoscopists. When the expert reviewers made different diagnosis, a final diagnosis was made by consensus. That was then compared with the diagnosis of the attending endoscopists at each hospital and their concordance was calculated separately for each endoscopy unit. In addition, the relationship between diagnostic accuracy and endoscopic experience was assessed.

RESULTS

The prevalence of BE diagnosis by the on-site endoscopists was not homogenous and varied widely (17.2-96.8%). In 1 hospital, over-diagnosis was the cause of dissimilarity, while under-diagnosis was the cause in two hospitals. Diagnostic accuracy by the attending endoscopists in all 4 hospitals ranged from 44.6 to 83.1% (P < 0.05). There was no significant association between diagnostic accuracy and endoscopic experience or board licensing status of the on-site endoscopists.

CONCLUSION

Diagnostic accuracy for BE was not homogenous among 4 hospitals, and problems related to over- and under-diagnosis should be considered.