Introduction to laboratory medicine

Lecture 4

Special chemistryDefinition

Special Chemistry is a subsection of the Chemistry Laboratory of the Division of Clinical Pathology. This includes the tests which are not the part of the routine panel.

ElectrophoresisUrine chemistryRadioimmunoassay.

Test Sensitivity and specificity

Troponin test

The most sensitive and specific test for myocardial damage. Because it has increased specificity compared with CK-MB, troponin is a superior marker for myocardial injury.

Myoglobin (Mb)low specificity for myocardial infarction. Rises very early within 1-3 hours of pain.

Pro-brain natriuretic peptide (pro-BNP)

This is increased in patients with heart failure. It has been approved as a marker for acute congestive heart failure

Glycogen phosphorylase isoenzyme BB

• high sensitivity and specificity early after chest pain.• by ELISA

Normal troponin levels 12 hours after chest pain has started mean a heart attack is unlikely

Myloperoxidase (MPO) Elevated in chronic conditions

CRP Marker of atherosclerosis

Pregnancy associated plasma protein A (PAPPA) elevated in atherosclerosis when atheroma is

about to ruptureOxidized LDL

A marker of atherosclerosisCholine

Test of prognosis Rises in chest discomfort even without rise in

troponin level.

Tumour markersA substance produced by tumour or by the host in response to tumour from normal tissues.

May be present in blood, urine or tissues.

Mostly they are antigens

May be cytoplasmic proteins, enzymes and hormones.

usesScreening

Example: elevated prostate specific antigen suggests prostate cancer.

Monitoring of cancer survivors after treatment. Example: elevated AFP

Diagnosis of specific tumor types, particularly in certain brain tumors and other instances where biopsy is not feasible

Be specific to the tumor

Level should change in response to tumor

sizeAn abnormal level should be obtained in

the presence of micrometastases

The level should not have large fluctuations that are independent of changes in tumor size

Levels in healthy individuals are at much lower concentrations than those found in cancer patients

Predict recurrences before they are

clinically detectable

Test should be cost effective

Ideal tumour marker

SCREENING TESTS

Cancer must be common

The natural history of the cancer should be understood

Effective treatments must be available

The test must be acceptable to both patients and physicians

The test must be safe and relatively inexpensive

GUIDELINES FOR ORDERING/INTERPRETING TUMOR MARKER TESTS

Never rely on the result of a single test

Order every test from the same laboratory

Consider half-life of the tumor marker when

interpreting the result.

Consider how the Tumor Marker is removed

or metabolized

Consider Hook Effect

Consider presence of HAMA antibodies

Detection techniquesSerology Enzyme assays

Immunological Immuno histo chemistry

Radio immuno assay

Enzyme-linked immuno sorbent assay

Flow cytometry

Cytogenetic analysis Fluorescent in-situ hybridization

Spectral karyotyping

Comparative genomic hybridization

Genetic analysis Sequencing (automated)

Reverse transcription

Gel electrophoresis

DNA micro-array analysis

Proteomics Surface-enhanced laser desorption/Ionization

Detection techniqueTumor markers can be detected by immunohistochemistry

Tissue selectionFixation.Tisue slicing by microtome.Antigen antibody reaction.Antibodies are labeled with some substance for detection enzyme, flurophore etc.Amplification

COMMON TUMOR MARKERSAnalyte Cancer Use

CEA Monitor colorectal, breast, lung cancer

CA-125 Ovarian cancer monitoring

AFP Germ cell tumors, liver cancer

Total PSAScreen and monitor prostate cancer

Free PSA Distinguish prostate cancer from BPH

HCG Germ cell and trophoblastic tumors

Hormone receptor

Breast cancer therapy

Benign conditions leading to high tumour marker level

MarkerAssociated nonmalignant

conditions

AFPViral hepatitis, liver injury, IBD, pregnancy

β-hCG Testicular failure, pregnancy

CEASmokers, IBD, hepatitis, cirrhosis, pancreatitis,gastritis

CA 125Peritoneal irritation, endometriosis, pelvic inflammatory disease, hepatitis, pregnancy

PAP / PSAProstatitis, benign prostatic hyperplasia

CEA

Described by Gold and Freedman in 1965 as a marker for Colorectal Cancer

Glycoprotein with a carbohydrate composition ranging from 50 - 85% of molecular mass

CEA levels 5 - 10 times upper limit of normal suggests colon cancer

CEA is not used to screen for colon cancer

AFPTumour marker of hepatocellular carcinoma, as

well as in the acute and chronic hepatitis.

Level is less than 10 ng/ml.

In person with no liver disease level upto 400ng/ml

means liver cancer. But in patients with infections

levels upto 4000ng/ml means liver cancer.

If tumour is removed fully with surgery then its

level should go back to normal.

After surgery if level rises again then it means that

tumour is back.

Tumor-associated Proteins Immunoglobulins,

markers β-2M

Enzymes Lactate

dehydrogenase,

alkaline phosphatase,

pteridines, pterines

Acute-phase C-reactive protein,

proteins ferritin

Inflammatory ESR, viscosity

makers

Ultrastructural Intermediate Desmin, vimentin

components filament components