ATale of Blood Chemistry and Health Abby Tudor recently turned 40 years old. Her knees ache, and she often feels short of breath during exercise. She is experiencing fatigue and often feels that she is going in slow motion Periodic dizziness plagues her during most days. Ac- cording to the drugstore machine, her blood pressure is elevated. Her family has a history of cardiac disease, with both of her parents having experienced heart at- tacks. Additionally, an aunt on her mother's side has diabetes. Hypothyroidism also runs throughout her immediate family. Abby is approximately 20 pounds overweight. She has tried various diet and exercise programs in an attempt to lose weight. Her results have been disappointing. With the advice of her physician, she scheduled an appointment for a full physical exam, including a complete blood workup. Her doctor is particularly interested in the level of various blood components that might shed some light on Abby' 5 reported symptoms. Specifically, he wants to examine her white blood cell count, red blood cell count, hemoglobin, and hematocrit gures for indications of infection or anemia. Her serum glucose level will provide information concerning the possibility of the onset of diabetes. Cholesterol and triglyceride levels will provide insight into potential cardiac problems. Additionally, the possibility of hypothyroidism will be investigated by examining Abby's serum TSH level. As instructed, two weeks before her doctor's appointment, she reported to her doctor's lab for a blood test. She conrmed for the lab technician that she had fasted for the 12 hours immediately preceding the exam. During her physical, Abby's doctor went over the blood test report with her. He expressed concern over some of the results, but Abby was not convinced that she had a problem. Additional blood tests were not a viable option because it takes a good deal of time to get a sample of readings and they are expensive. At the time of her doctor's appointment, she was unwilling to accept the offered prescriptions. She chose to do a little research before committing herself to any drug regimen. Her research revealed that many medical measurements, such as cholesterol, are normally distributed in healthy populations. Unfortunately, the lab report did not provide the means and standard deviations necessary for Abby to calculate the various probabilities of interest. However, the report did pro- vide the appropriate reference intervals. Assuming that the reference intervals represent the range of values for each blood component for a healthy adult population, it is possible to estimate the various means and standard deviations for this population. Abby estimated each mean by taking the midpoint of its reference interval. Using the Range Rule of Thumb (o :Range/Al), standard deviations were estimated by dividing the reference interval range by 4. The following table lists Abby's blood test results, as well as the mean and standard deviation for a number of blood test components for the population of normal healthy adults. For any blood component measurement that was below its population mean, Abby decided to calculate the probability that she would get a test value equal to the value obtained or less, given that she was a member of the healthy population. For example, her Creatine, serum reading (0.8 mg/dL) was below the mean of the healthy population (1.0 mg/dL), so she calculated the following probability: PtX g 0.8 mgldL) Chapter 7 Case Study Blood Test Components for Healthy Adults and the Blood Test Results for Abby Tudor* Abby's Abby's Standard Absolute Blood Test Component Unit Mean Deviation Result White blood cell count 103/mL 7.25 1.625 3.3 Red blood cell count 105/mL 4.85 0.375 4.62 Hemoglobin g/dL 14.75 1.125 10.6 Hematocrit 43.0 3.5 41.7 Glucose, serum mg/dL 87.0 11.0 95.0 Creatine, serum mg/dL 1.00 0.25 0.8 Sodium, serum mEq/L 141.5 3.25 143.0 Potassium, serum mEq/L 4.5 0.5 5.1 Chloride, serum mEq/L 102.5 3.25 100.0 Carbon dioxide, total mEq/I 26.0 3.0 25.0 Calcium, serum mg/dL 9.55 0.525 10.1 Total cholesterol mg/dL 149.5 24.75 253.0 Triglycerides mg/dL 99 5 49.75 150.0 HDL cholesterol mg/dL 92.5 28.75 22.0 LDL cholesterol mg/dL 64.5 32.25 150.0 LDL/HDL ratio Ratio 1.8 0.72 4.3 TSH, high sensitivity, serum mcIU/mL 2.925 1.2875 3.15 .. Population means and standard deviations were estimated from the reference intervals derived from an actual blood test report provided by TA LabCorp, Tampa, Florida. Means were estimated by taking the midpoints of the reference intervals. Standard deviations were estimated by dividing the reference interval ranges by 4. Testresults attributed to Abby Tudor are actual results obtained from an anonymous patient. Similarly, for any blood component measurement reading exceeding its population mean, Abby decided to calculate the probability that she would get a test value equal to the value obtained or more, given that she was a member of the healthy population. For example, her LDL/HDL ratio value (4.3 mg/dL) exceeds the mean of the healthy population (1.8 mg/dL), so she calculated the following probability: P(X 2 4.3 mg/dL) To help her interpret the calculated probabilities, Abby decided to be con- cerned about only those blood components that had a probability less than 0.025. By choosing this figure, she is acknowledging that it is unlikely that she could have such an extreme blood component reading and still be part of the healthy population. 1. The reference interval for HDL cholesterol is 35 to 150 mg/dL. Use this information to confirm the mean and standard deviation provided for this blood component. 2. Using Abby's criteria and the means and standard deviations provided in her blood test report, determine which blood components should be a cause of concern for Abby. Write up a summary report of your findings. Be sure to include a discussion concerning your assumptions and any limi- tations to your conclusions