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

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

临床实验室的地位和作用

THE USE OF BIOCHEMICAL TESTS

试验检查的过程

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.

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

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

Emergency testsUrea and electrolytes

Blood gases

Amylase

Glucose

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.

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

SAMPLING ERRORS

Blood sampling techniqueProlonged stasis during venepuncture. Insufficient specimen Errors in timing Incorrect specimen container Inappropriate sampling site Incorrect specimen storage

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.

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.

Case 1A 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?

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.

VARIATION IN RESULTS

Laboratory measurements vary for two reasons ----- analytical variation

biological variation

Laboratory analytical performance

A number of terms describe laboratory results. These include:

        precision and accuracy        sensitivity and specificity        quality assurance        reference ranges

Precision and accuracy Precision is the reproducibility of an

analytical method. Accuracy defines how close the

measured value is to the actual value.

Sensitivity and specificity Sensitivity of an assay is a measure of how li

ttle of the analyte the method can detect. Specificity of an assay relates to how good th

e assay is at discriminating between the requested analyte and potentially interfering substances.

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)

Reference ranges

Laboratory test results are usually compared to a reference range considered to represent the normal healthy state.

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.

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.

Biological factors affecting the interpretation of results

  Sex of the patient. Reference ranges for some analytes are different for men and women.

  Age of the patient. There may be different reference ranges for neonates, children, adults and the elderly.

Effect of diet. The sample may be inappropriate if taken when the patient is fasting or after a meal.

  Time when sample was taken. These may be variations during the day and night.

Stress and anxiety. These may affect the analytes of interest.

  Posture of the patient. Redistribution of fluid may affect the result.

 Effects of exercise. Strenuous exercise can release enzymes from tissues.

  Medical history. Infection and/or tissue injury can affect laboratory values independently of the disease process being investigated.

   Pregnancy. This alters some reference ranges.  Menstrual cycle. Hormone measurements will vary through the m

enstrual cycle.  Drug history. Drugs may have specific effects on the plasma conc

entration of some analytes.

The clinician may well ask the following questions on receiving a laboratory report:

 Does the result fit in with what I expected on the basis of the clinical examination and history of the patient?

If the result is not what I expected, can I explain the discrepancy?

 How can the result change my diagnosis or the way I am managing the patient?

  What should I do next?

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

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”.

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.

Case 2A 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?

Thank you