Combination (multiple) testing for myocardial infarction using myoglobin, creatine kinase-2 (mass), and troponin T.

We retrospectively determined the mass concentrations of myoglobin, creatine kinase-2 (CK-2), and troponin T in serial samples from 80 patients with confirmed myocardial infarction (MI) and 60 non-MI patients. Results from receiver operating characteristic curve analyses show that all three tests are comparable in their diagnostic utility within the first 12 h of infarction. Decision thresholds were selected at a constant rule-in specificity of 95% and rule-out sensitivities of 95% at, respectively, 3-6, 6-9, and 9-12 h intervals after the onset of symptoms. Test sensitivities and specificities were compared for each, used as: a single test; two-test parallel combination; three-test parallel combination; two-test series combination; and three-test series combination. Our results from combination testing indicate what for the early diagnosis of MI, a single serum myoglobin measurement has diagnostic utility at 3 h after the onset of symptoms, and myoglobin and CK-2 (mass) in combination later than 3 h following the onset of symptoms. Serum troponin T is diagnostically similar to CK-2 (mass), although it has superior cardiac-tissue specificity, but it is not as yet commercially available as a "stat" test. Therefore, we recommend using troponin T as a confirmatory test 9 h after the onset of MI. Based on our findings, we suggest a testing algorithm for the early biochemical diagnosis of MI.

Reference intervals for blood lead and evaluation of zinc protoporphyrin as a screening test for lead toxicity.

We evaluated, retrospectively, 2921 blood samples for the distribution of blood lead values in children below age 16, and in adult female and male subjects. An upper reference value for children and females at 0.48 mumol/L, and for males at 0.72 mumol/L is used. Over 70% of the adult males and > 80% of the children and adult females were within these reference limits, and considered to be at low risk for lead toxicity. The diagnostic utility of zinc protoporphyrin (ZPP) to screen for a positive blood lead result was evaluated using receiver operating characteristic (ROC) curves and likelihood ratios (LR). These studies confirmed that ZPP was insensitive for the detection of elevated blood lead at the critical thresholds of 0.48-1.21 mumol/L in children and adult females with subclinical lead poisoning. ZPP was more diagnostically useful for screening the higher lead-exposed adult male occupational worker.

The freckle plot (daily turnaround time chart): a technique for timely and effective quality improvement of test turnaround times.

Test turnaround times are often monitored on a monthly basis. However, such an interval usually means that not all causes for delay in test reporting can be unequivocally identified for institution of remedial action. We have devised a daily chart--the freckle plot--that graphically displays the test turnaround times by laboratory receipt time. Different symbols are used to designate specimens reported within the test's turnaround time limit, those within 10 min beyond that limit, and those well outside the limit. These categories are adjustable to suit different limits of stringency. Freckle plots are produced on a daily basis and can be used to track down causes for test delays. Using the 1-h turnaround time "stat" potassium test as a model, we found 16 causes for test delay, of which 9 were potentially remediable. By applying these remedies, we were able to increase test compliance, in the day shift, from 91.5% (95% confidence interval 88.8%-93.7%) to 97.6% (95% confidence interval 96.4-98.55%), which is significant at P < 10(-7). This daily plot is a useful quality assurance tool, supplementing the more conventional tests used to ensure laboratory quality improvement.

A computer program to determine diagnostic decision thresholds and likelihood ratios illustrated with aspartate aminotransferase activities after a myocardial infarction.

We describe an enhancement of our earlier computer program which allows calculation of decision thresholds, sensitivity and specificity, and likelihood ratios of negative and positive test results for any chosen value of sensitivity or specificity. The program will also plot continuous receiver operating characteristic and decision level curves which permit examination of the contours created by using all the available data. We illustrate the value of these routines by showing that the sensitivity and specificity of serum aspartate aminotransferase changes during the course of a myocardial infarction.

A computer program for rapid generation of receiver operating characteristic curves and likelihood ratios in the evaluation of diagnostic tests.

We describe a MUMPS program to facilitate the evaluation of the diagnostic effectiveness and efficiency of laboratory tests using receiver operating characteristic (ROC) curves and likelihood ratios (LR). Test results from a population with and without a disease are stored into retrievable, editable data bases. Either single or a combination (less than or equal to 9) of different test data files can be accessed to generate tables of calculated frequency distribution, sensitivity, l-specificity and LR at variable decision thresholds. The program also calculates the area under the ROC curve, confidence intervals and SE. The selection of the optimum cut-off value is assisted by graphical plots of frequency distribution, ROC and decision level curves as illustrated by using some 'cardiac' enzyme tests.