Chemistry Test 1 2012

The correct answer is "All the above" because chemistry is a science that can be difficult to understand, frustrating at times, and may seem stupid to some individuals.

The clinical sensitivity is calculated by dividing the number of true positive results (patients who tested positive for sickle cell disease) by the total number of patients diagnosed with the disease. In this case, there were 72 true positive results out of 80 patients diagnosed with sickle cell disease. Therefore, the clinical sensitivity is 90%.

Using an incorrect colored-stopper tube to obtain a blood sample is referred to as a preanalytical variable. This means that the error occurred before the analysis of the blood sample took place. The correct choice is "preanalytical" because it accurately describes the situation where the mistake in using the wrong colored-stopper tube happened before the actual analysis of the blood sample.

A "bidirectional interface" between an LIS and a chemistry analyzer's computer means that the analyzer and the LIS can communicate ordering information and test results between them. This allows for seamless data exchange and eliminates the need for the laboratorian to manually enter results into both systems. The bidirectional interface enables efficient and accurate communication between the analyzer and the LIS, improving workflow and reducing the chances of errors in result entry.

Bias can be defined as systematic error because it refers to a consistent deviation from the true value or an unfair inclination towards a particular outcome. Systematic bias occurs when there is a flaw or a consistent pattern in the data collection or analysis process that leads to inaccurate or skewed results. It is different from random error, which is unpredictable and does not follow a consistent pattern. Analytical and clinical errors may contribute to bias, but they do not specifically capture the consistent nature of systematic bias.

In regard to a gaussian distribution, + or - 2 SD's from the mean encompasses 95.5% of values. This is because in a normal distribution, approximately 95.5% of the data falls within two standard deviations of the mean. This is known as the empirical rule or the 68-95-99.7 rule, which states that about 68% of the data falls within one standard deviation, about 95% falls within two standard deviations, and about 99.7% falls within three standard deviations of the mean.

Analytical sensitivity refers to the lowest concentration of analyte that can be detected and accurately quantitated. It is a measure of the assay's ability to detect and measure small amounts of the analyte in a sample. A higher analytical sensitivity means that the assay can detect lower concentrations of the analyte, making it more sensitive and capable of accurately quantitating even very low levels of the analyte in a sample. Therefore, the correct answer is "Lowest concentration of analyte that can be detected and accurately quantitated."

RAM (Random Access Memory) is a type of computer memory that is volatile, meaning its contents are lost when the computer is turned off or loses power. Unlike ROM (Read-Only Memory) which retains its data even when power is lost, RAM is used for temporary storage of data that the computer is actively using. Therefore, each time the computer is turned off, the content stored in RAM is erased, making it the correct answer to the question.

The correct answer is "compares the means of two samples using sample statistics." The students t-test is a statistical test used to determine if there is a significant difference between the means of two independent samples. It compares the means of the samples using the sample statistics, such as the sample mean and sample standard deviation, rather than the population parameters. This test helps to assess whether the observed difference in means is statistically significant or occurred by chance.

Assayed control refers to a substance with an assigned value that the manufacturer establishes by using a reference method or by using reference materials traceable to primary standards. This means that the manufacturer determines the value of the substance by comparing it to established standards or methods. This ensures that the substance is accurately measured and allows for quality control in laboratory testing.

Pipetting errors can be considered an example of random error because they can occur unpredictably and affect the accuracy of measurements. Mistakes in pipetting, such as incorrect volume or improper technique, can lead to variations in the amount of substance being transferred, resulting in inconsistent results. These errors are not systematic or consistent, but rather occur randomly and can be caused by factors such as human error, equipment malfunction, or environmental conditions.

The correct answer is "Plot cumulative frequency versus test value on probability paper and determine test values at 2.5% and 97.5%". This method is used to calculate the reference interval for the healthy population. By plotting the cumulative frequency versus test value on probability paper, it allows for a visual representation of the distribution of test results. The 2.5% and 97.5% values on the plot represent the lower and upper bounds of the reference interval, respectively, capturing the range within which 95% of the healthy population's test results fall.

During diagnostic accuracy studies in evidence-based laboratory medicine, a laboratory test being studied is compared with the "gold standard" of testing, which is the currently used assay or assay system. The test method being studied is referred to as the candidate/reference method because it is being evaluated as a potential alternative or replacement for the current standard method.

The correct answer is "Only a and c". The ROC (Receiver Operating Characteristic) curve is a statistical tool used to evaluate the performance of a binary classification model. Sensitivity, also known as the true positive rate, measures the proportion of actual positive cases correctly identified by the model. The ROC curve aims to maximize sensitivity. FPR (False Positive Rate) measures the proportion of actual negative cases incorrectly identified as positive by the model. The ROC curve aims to minimize FPR. Therefore, the correct answer is "Only a and c" as it includes the options that prioritize both sensitivity and the lowest FPR.

The method of specimen collection must be standardized when establishing a reference interval for an analyte. This is because different methods of specimen collection can introduce variability in the results, which can affect the reference interval. Standardizing the method of specimen collection ensures consistency and accuracy in the results, allowing for a reliable reference interval to be established. The other factors mentioned (location in which venipuncture is performed, reagents used in analyte analysis, and the specific method used for analysis) may also impact the results, but the method of specimen collection is specifically mentioned as the factor that must be standardized.

Diurnal variation refers to the natural fluctuation of cortisol levels throughout the day. Cortisol is typically highest in the morning (am) and decreases as the day progresses, reaching its lowest point in the evening (pm). Therefore, if a patient's serum am cortisol was higher than the pm value, it can be explained by diurnal variation. This is a normal physiological response and does not necessarily indicate any underlying medical condition or issue with the specimen.

In setting the criteria for a delta check for a specific patient, it is important to consider physiological variation. Physiological variation refers to the natural changes that can occur in a patient's test results due to factors such as time of day, age, or overall health. By taking into account these variations, healthcare professionals can establish appropriate thresholds for detecting significant changes in a patient's test results over time. This helps in identifying potential abnormalities or trends that may require further investigation or intervention.

The value for standard deviation interval cal (SDI) can be calculated by subtracting the group mean from the laboratory reported value and then taking the absolute value of the difference. In this case, the laboratory reported value is 2.55 mmol/L and the group mean is 2.50 mmol/L. So, the difference is 2.55 - 2.50 = 0.05 mmol/L. Taking the absolute value, we get 0.05 mmol/L. Therefore, the value for standard deviation interval cal (SDI) is 0.05.

Discriminator values are associated with tests that have high sensitivity and low false positive rate (FPR) towards a specific disease. This means that these tests are able to correctly identify individuals who have the disease (high sensitivity) while minimizing the number of false positive results (low FPR). In other words, these tests have a high ability to accurately detect the presence of the disease while minimizing the chances of incorrectly identifying individuals without the disease as positive.

Method selectivity/specificity refers to the degree to which the method is free from interference by other species in the sample. This means that the method is able to accurately measure the analyte of interest without being affected by other substances present in the sample. It indicates the ability of the method to differentiate and measure the target analyte specifically, without any interference from other compounds.

The percent accuracy (error) can be calculated by subtracting the value obtained on the analyzer (200 umol/L) from the assayed control value (220 umol/L), dividing the result by the assayed control value, and then multiplying by 100. In this case, the calculation would be: ((200 - 220) / 220) * 100 = -9.1. Therefore, the percent accuracy (error) is -9.1.

In this scenario, by assaying a control sample multiple times and analyzing the mean and variance of the results, the aim is to determine the precision of the instrument. Precision refers to the consistency and reproducibility of measurements. By examining the variability of the results, one can assess how closely the measurements cluster around the mean value. Therefore, in this case, the focus is on evaluating the precision of the new hormone analyzer.

Prevalence affects the detection rate. Detection rate refers to the proportion of true positive cases that are correctly identified by a test. When the prevalence of a condition is high, the likelihood of detecting true positive cases increases, leading to a higher detection rate. Conversely, when the prevalence is low, the detection rate may decrease as there are fewer true positive cases to be detected. Therefore, the prevalence of a condition has a direct impact on the detection rate of a test.