Biochemical investigations in clinical medicine

Transcription

1 Biochemical investigations in clinical medicine Presented by Dr. Mohammad Saadeh The requirements for the Clinical Chemistry Philadelphia University Faculty of pharmacy

2 Introduction What it is? Clinical chemistry (also known as chemical pathology, clinical biochemistry or medical biochemistry) is the area of clinical pathology that is generally concerned with analysis of bodily fluids for diagnostic and therapeutic purposes. Note: (not to be confused with medicinal chemistry).

3 Use of biochemical investigation vvi Why it is? Clinical chemistry provided biochemical information for the management of patients. Biochemical investigation are for: 1. diagnosis, 2. prognosis, 3. monitoring, 4. screening. 1. Diagnosis Diagnosis used for conformation or rejection of clinical diagnosis 2. Prognosis Investigations used for diagnosis may provide prognostic information. Example: the risk of coronary artery disease increase with increasing plasma cholesterol concentration.

4 Use of biochemical investigation vvi 3. Monitoring A major use of biochemical investigations is to follow the course of an illness and to monitor the effects of treatment. Example: 1. Glycated haemoglobin in patients with diabetes mellitus. 2. Detect complication of treatment such as hypokalaemia during treatment with diuretics. 4. Screening Biochemical investigation used to determine whether a condition is present subclinically. Example: mass screening of all newborn babies for phenyketonuriua (PKU).

5 Use of biochemical investigation vvi

6 Specimen Collection A. The test request The specimen for analysis must be collected and transported to the laboratory according to a specific procedure. The request should include: Patients name, sex, and date of birth Hospital or other identification number Ward/clinic/address Name of requesting doctor (telephone) Clinical diagnosis/problem Test (s) requested Type of specimen Date and time of sampling Relevant treatment (e.g. drugs) The omission of any of the above may cause delay in analysis and reporting or make it impossible to interpret the results.

7 Specimen Collection B. The patient Some analysts are affected by variables such as posture, time of day, etc. Example: Age: alkaline phosphatase increase in children. daily measurements of fasting blood glucose concentration. Exercise: creatine kinase increase. C. The specimen: Most biochemical test are made on: 1. Serum 2. plasma 3. whole blood 4. urine 5. cerebrospinal fluid (CSF) 6. aspirates (example; pleural fluid, ascites, joint fluid) 7. tissue & cells 8. faeces 9. Calculi (stones). 10. Sputum & saliva. Figure 1.2 page 3

8 Specimen Collection vvi Blood specimen: 1. serum If blood collected into tube and allowed to clot, after centrifugation a serum specimen is collect. serum is the blood fluid without the clotting factors. 2. plasma If blood collected into tube containing an anticoagulant such as heparin, after centrifugation a plasma specimen is collect. Plasma is the blood fluid that carries blood clotting agents (Fibrinogen) Haemolysis must be avoided when blood is drawn Collection a blood specimen into the wrong container lead to erroneous results. (See figure 1) Degradation of labile analyte must be prevented by refrigerating or freezing the serum or plasma.

9 Specimen Collection VVI

10 Specimen Collection VVI Urine specimen: Urine specimen containers may include a preservative to inhibit bacteria growth, or acid to stabilize certain metabolites. Sampling errors: Blood sampling: Haemolysis must be avoided when blood is drawn Incorrect sampling container: Collection a blood specimen into the wrong container lead to erroneous results. Incorrect specimen storage: Degradation of labile analytes must be prevented by refrigerating or freezing the serum or plasma.

11 Urgent requests Some requests tests will be urgent in that their results may have an immediate bearing on the management of patient. Example: 1. Measurement of serum paracetamol concentration in patient who taken overdose. 2. Measurement troponin concentration in patient with chest pain. 3. Measurement of serum potassium in patient with acute kidney. Repeat requesting: This will depend on both physiological and pathological factors. Example: Several weeks need for the plasma concentration of thyroid stimulating hormone (TSH) to stabilize a dose of thyroxin.

12 Point of care testing VVI Biological compounds in blood and urine can be made away from laboratory by patients beside, in the home in the shopping center. Advantage: 1. immediate 2. quick Example: blood glucose. Category the tests can be made away from laboratory: 1. Test performed in medical to: reassure the patient or further investigations or treatment. 2. Test performed in the home: to give valuable information (ex; glucose). 3. Alcohol tests: used to assess fitness to drive.

13 The interpretation of results Point must be taken into consideration when the result of biochemical test is obtained: Is it normal? Is it different? Is it consistent with clinical findings? Results are terms in: Concentration: mmol/l or mg/l. Enzyme activity: enzyme unite (U); that is the amount that catalyzes the conversion of 1 micromole of substrate per minute. Blood gas (PCO 2 or PO 2 ): Kilopascals (KPa); pressures unit.

14 Variation in results 1. Analytical variation: Collected wrong specimen, mislabeling, incorrect preservation. The error from human or instrumental. Incorrect recorded. 2. Biological variation: Actual changes in patients body fluids. A number of terms describe biochemical results: Precision and accuracy Sensitivity and specificity

15 Precision and accuracy VVI Precision: is the reducibility of an analytical method (the ability of an entire experiment to be duplicated). Accuracy: is how close a measured value is to the actual (true) value..

16 Sensitivity and specificity Sensitivity: This is the percentage of positive results for a test in patients with the particular disease. Sensitivity = (TP) / (TP+FN) x100% True positive = Positive that are correctly identified False negative= negative that are incorrectly identified Specificity: This is the percentage of negative results in people known or subsequently proved to be free from the particular disease. Specificity = (TN) / (TN+FP) x 100% True negative (TN): negative that are correctly identified. False positive (FP): positive that are incorrectly identified.

17 The accuracy of an evaluated test calculated as following Reference Test + ve - ve + ve True positive (TP) False positive (FP) Evaluated Test - ve False negative (FN) True negative (TN) Total TP+ FN FP+ TN Total TP+FP FN+TN TP+ FN+ FP+ TN Sensitivity = (TP) / (TP+FN) x100% Specificity = (TN) / (TN+FP) x 100% = 100% Efficiency = (TP+TN) / (TP+FP+FN+TN) x100% Positive Predictive Value (PPV) = (TP) / (TP+FP) x100% Negative Predictive Value (NPV) = (TN) / (FN+TN) x100%

18 Group n Detection of antigen using ELISA +ve -ve Total Healthy individuals Bladder Cancer (Low grade; G1) 40 2 (FP) 38 (TN) (TP) 1 (FN) 12 Total Sensitivity = Tp / (Tp + Fn) 100 = 11 / (11 +1) 100=92% Specificity = Tn / (Tn + Fp) 100 = 38 / (38 +2) 100=95% PPV = Tp / (Tp + Fp) 100 = 11 / (11 +2) 100=85% NPV = Tn / (Tn + Fn) 100 = 38 / (38 + 1) 100=97% Efficiency = Tp + Tn / (total number of subject) 100 = / (65) 100=94%

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