HOW TO USE CLINICAL LABORATORY

1. HOW TO USE CLINICAL LABORATORY Li Ping 李萍 Department of Laboratory Medicine 检验系/实验医学 West China Hospital and Medical School of Sichuan University

2. Organization of the Department 实验医学科 • 临床微生物室 • 临床血液及临检室 • 临床免疫室 • 临床生化室 • 临床激素室 • 临床输血室 • 临床药理室

3. 临床实验室的地位和作用

5. THE USE OF BIOCHEMICAL TESTS

6. 试验检查的过程

7. Every laboratory analysis should provide the answer to a question which the clinician has posed about the patient. Obtaining the correct answers can often seem to be fraught with difficulty.

8. 申请单条码号、门诊号、住院号 病人的姓名、性别和出生日期 病房、床位号 临床诊断、特殊检验注意事项 申请检查项目 标本类型 采样时间及报告时间（年、月、 日、时、分） 有关治疗情况（如：用药情况） 医生姓名

9. Specific Groupings of Tests 01 生化1 常规全套 (肝肾糖尿酸脂酶） 04 生化4 K Na Cl Ca Mg P 05 生化5 K Na Cl CO2 06 肝功 （TB DB IB ALT TP Alb Glob A/G AST) 07 肾功 （Urea Crea) 08 肝酶 （AST ALP GGT LDH CHE) 12 碱性磷酸酶 ALP

10. Emergency tests Urea and electrolytes Blood gases Amylase Glucose

11. Clinical note The clinical laboratory plays only a part in the overall assessment and management of the patient. For some patients, laboratory analyses may have little or no part in their diagnosis or the management of their illness. For others, many test may be needed before a diagnosis is made, and repeated analyses required to monitor treatment over a long period.

12. SPECIMEN COLLECTION • Provide correct specimen and information • As much information as possible • Patient identification must be correct • Include some indication of the suspected pathology • Requested analyses should be clearly indicated

13. SAMPLING ERRORS • Blood sampling technique • Prolonged stasis during venepuncture. • Insufficient specimen • Errors in timing • Incorrect specimen container • Inappropriate sampling site • Incorrect specimen storage

15. AUTOMATION AND COMPUTERIZATION Computerized laboratories and automated methods of analysis allows a high degree of productivity and improves the quality of service. Laboratory informational system (LIS) Linked to computer terminals on wards allow direct access to results by the requesting clinician.

16. Summary • Each laboratory test request should be thought of as a question about the patient, each result as an answer. • Request forms and specimens must be correctly labeled to ensure that results can be communicated quickly to the clinician. • A variety of sampling errors may invalidate results.

17. Case 1 A blood specimen was taken from a 65-year-old woman to check her serum potassium concentration as she had been on thiazide diuretics for some time. The nurse left the specimen in clinic and sent to the laboratory next morning. Immediately on analyzing the sample, the biochemist was on the phone to the ward. Why?

18. THE INTERPRETATION OF RESULTS • THE LABORATORY REPORT It can take considerable effort, and expense, to produce what may seem to be just numbers on pieces of paper. Understanding what these numbers mean is of crucial importance if the correct diagnosis is to be made, or if the patient’s treatment is to be changed.

19. VARIATION IN RESULTS Laboratory measurements vary for two reasons ----- analytical variation biological variation

20. Laboratory analytical performance A number of terms describe laboratory results. These include: lprecision and accuracy lsensitivity and specificity lquality assurance lreference ranges

21. Precision and accuracy Precision is the reproducibility of an analytical method. Accuracy defines how close the measured value is to the actual value.

22. Sensitivity and specificity Sensitivity of an assay is a measure of how little of the analyte the method can detect. Specificity of an assay relates to how good the assay is at discriminating between the requested analyte and potentially interfering substances.

23. Quality assurance(QA) Laboratory staff monitor performance of assays using quality control samples to give reassurance that the method is performing satisfactorily with the patients’ specimens. Internal quality controls (IQC) External quality assurance (EQA)

24. Reference ranges Laboratory test results are usually compared to a reference range consideredto represent the normal healthy state.

26. There is often a degree of overlap between the disease state and the ‘normal value’. A patient with an abnormal is a false positive. A patient who has the disease but has a ‘normal’ result is a false negative.

27. In practice there are no rigid limits Demarcating the diseased population from the healthy; however, the further a result is from the limits of the range, the more likely it is to represent pathology.

28. Biological factors affecting the interpretation of results lSex of the patient. Reference ranges for some analytes are different for men and women. lAge of the patient. There may be different reference ranges for neonates, children, adults and the elderly. lEffect of diet. The sample may be inappropriate if taken when the patient is fasting or after a meal. lTime when sample was taken. These may be variations during the day and night. • Stress and anxiety. These may affect the analytes of interest.

29. lPosture of the patient. Redistribution of fluid may affect the result. lEffects of exercise. Strenuous exercise can release enzymes from tissues. lMedical history. Infection and/or tissue injury can affect laboratory values independently of the disease process being investigated. lPregnancy. This alters some reference ranges. lMenstrual cycle. Hormone measurements will vary through the menstrual cycle. lDrug history. Drugs may have specific effects on the plasma concentration of some analytes.

30. The clinician may well ask the following questions on receiving a laboratory report: lDoes the result fit in with what I expected on the basis of the clinical examination and history of the patient? lIf the result is not what I expected, can I explain the discrepancy? lHow can the result change my diagnosis or the way I am managing the patient? lWhat should I do next?

31. 影响生化检验结果的重要因素 因 素 生化检验项目 年龄 胆固醇、尿酸、碱性磷酸酶 性别 性腺激素 体重 甘油三酯 时间 皮质醇（昼夜变化） 促性腺激素（女性月经周期变化） 25-羟维生素D3（季节变化） 紧张 皮质醇、催乳素、生长激素、儿茶酚胺 葡萄糖 体位 肾素、醛固酮、血浆蛋白 饮食 葡萄糖、甘油三酯、磷酸盐

32. What is done in response to a laboratory report rests with the clinical judgment of the doctor. There is a maxim that doctors should always“treat the patient, rather than the laboratory report”.

33. Clinical note It is important to realize that an abnormal result does not always indicate that a disease is present, nor a normal result that is not. Beware of over reacting to the slightly abnormal result in the otherwise health individual.

34. Case 2 A serum potassium concentration of 45 mmol/L was recorded in the notes of a 35-year-old man being prepared for appendicectomy. The set of electrolyte results had been phoned from the laboratory. The surgeon was unperturbed, after he did check the results on the ward terminal himself. Why?

35. Thank you