LABORATORY TEST AND INTERPRETATION

LECTURE BY

DR AGYEMA J P

Introduction

• Lab studies are an extension of physical examination in which tissue, blood, urine or other specimens are obtained from patients and subjected to microscopic, biochemical, microbiological or immunological examination.

What does lab result mean?

What are false-positive and false-negative test results?

• A false-positive test result is one that shows a disease or condition is present when it is not present.

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• A false-positive test result may suggest that a person has the disease or condition when he or she does not have it.
• For example, a false-positive pregnancy test result would appear to detect the substance that confirms pregnancy. when in reality the woman is not pregnant.

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contd

• A false-negative test result is one that does not detect what is being tested for even though it is present.
• A false-negative test result may suggest that a person does not have a disease or condition being tested for when he or she does have it.
• For example, a false-negative pregnancy test result would be one that does not detect the substance that confirms pregnancy, when the women really is pregnant.

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What if your results are different than the reference range?

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• It is possible that is different than the reference range even though nothing is wrong with you.
• Sometimes certain factors can affect your test results, such as:
• Pregnancy, Medicine you are taking , Eating right before a test , smoking Being under stress

Why do values or reference ranges vary from lab to lab?

• Labs may use different types of equipment and tests, and sometimes they set their own reference ranges.
• Lab report will contain the reference ranges the lab uses.
• Do not compare results from different labs.

COMPLETE BLOOD COUNT(CBC)

• The CBC (with or without differential) is one of the most common blood tests.
• The CBC can help detect blood diseases and disorders, such as anemia, infections, clotting problems, blood cancers and immune system disorders.
• Peripheral venous blood is collected in a lavender tube (contains the anticoagulant EDTA ) and should be thoroughly mixed
• Unacceptable specimen: Clotted or greater than 48 hours old

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CBC contd

• Red Blood Cells SI unit (normal value) : Male 4.3-5.9*106/mL Female 3.5-5.0*106/mL
• Deficiency of RBC: 1. Hemolytic anemia: decrease no of RBC 2. Excess bleeding 3. Hereditary spherocytosis
• Elevation of RBC: 1. Polycythemia: Over production of RBC Primary polycythemia : caused by overproduction of red blood cells by the bone marrow due to mutation or biological factor in the body.
• Secondary polycythemia: which is caused by factors that reduce the amount of oxygen reaching the body's tissues, such as smoking, high altitude or congenital heart disease.

Red blood cell enzyme disorders:

• Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an X- linked disorder most commonly characterized by episodic haemolysis in the setting of oxidative triggers, such as fava beans, infections, and certain medications.
• Enzymopathies, such as pyruvate kinase deficiency, should be suspected in patients of all ages with a chronic haemolytic anaemia in the absence of immune-mediated haemolysis,
• hemoglobinopathy

• Mean Corpuscular Volume (MCV): MCV is a measure of the average size of the RBC.
• Abnormal MCV levels may be a sign of anaemia or thalassemia. Normal value : 76-100 mm3
• Macrocytic: increase RBC size
• Microcytic: decrease RBC size

WBC

• White Blood Cells SI unit (normal value) : 4000–11000/μL
• Neutrophils , Eosinophil’s,, Lymphocytes, Monocytes and basophils

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• Leukopenia: decrease no of WBC
• Neutropenia: decrease no of neutrophils ( aplastic anemia, chemotherapy, myelodysplasia, typhoid fever, hyperglycemia)
• Basopenia
• lymphocytopaenia (viral infection, systemic lupus erythematosus (SLS), rheumatoid arthritis, myasthenia gravis)
• Monocytopenia: decrease no of monocytes (MonoMac Syndrome (the risk of infection with certain organisms, including a group of bacteria known as Mycobacterium avium complex (MAC) that are related to tuberculosis, human papillomavirus (HPV), and certain fungi.

WBC

• Elevation in WBC: 1. Leukocytosis: increase no of WBC (>11000/μL)
• Neutrophilic leukocytosis: increase no of neutrophils
• Basophilia: increase no of basophils (hypothyroidism, myeloproliferative disorders)
• Eosinophilia: increase no of eosinophils (parasitic and fungal disease, allergies, skin disorders, toxins)
• Lymphocytic leukocytosis: increase of lymphocytes
• Monocytosis: increase no of monocytes (sarcoidosis, and Langerhans cell histiocytosis, autoimmune disorder)

Platelets

• Platelets SI unit (normal value) : 150000-450000/μL
• Thrombocytopenia: low number of platelets
• Thrombocytosis : increase number of platelets (acute bleeding and blood loss, cancer, infections, removal of spleen,
• Blood clotting test:
• Factor V assay: This test measures Factor V, a substance involved in clotting. An abnormally low level may be indicative of liver disease, primary fibrinolysis (a breakdown of clots), or disseminated intravascular coagulation (DIC).
• Fibrinogen level Fibrinogen is a protein made by your liver. This test measures how much fibrinogen is in your blood. Abnormal results may be a sign of excessive bleeding or hemorrhage, fibrinolysis, or placental abruption, which is a separation of the placenta from the uterine wall.

• Prothrombin time (PT or PT-INR) Prothrombin is another protein that the liver produces.
• The prothrombin time (PT) test measures how well and how long the blood takes to clot.
• Normal clotting time is about 25 to 30 seconds. It may take longer if one takes blood thinners.
• Other reasons for abnormal results include hemophilia, liver disease, and malabsorption. It’s also useful in monitoring those who take medications that affect clotting, such as warfarin (Coumadin).
• Typical reference ranges for healthy adults are: Blood clotting test Time/ concentration PT 9.0-11.7 sec INR (coumadin) 0.9-1.2 sec PTT (Heparin monitoring) 55.0-75.0 sec APTT (therapeutic) 23.3-31.9 sec Fibrinogen 203-377 mg/dl

HAEMOGLOBIN

• Hemoglobin SI unit (normal value) : Male 14–18 g/dL Female 12–16 g/dL
• Normocytic: hemoglobin levels are decrease but RBC size is normal (acute blood loss, anemia of chronic disease.
• Microcytic: insufficiency of hemoglobin synthesis (iron deficiency of anemia, thalassemia)
• Macrocytic: deficiency of vitamin B1 or folic acid (hypothyroidism, alcoholism) Sickle cell anemia: alteration in hemoglobin structure Hematocrit: Hematocrit is a measure how much space red blood cells take up in your blood.
• A high hematocrit level might mean dehydrated.
• A low hematocrit level might mean have anemia.
• Abnormal hematocrit levels also may be a sign of a blood or bone marrow disorder.

CARDIAC LAB TEST

• Laboratory test for Cardiac vascular system
• Troponin: when muscle or heart cells are injured, troponin leaks out, and its level in blood is rise. Blood level of troponin rise when you have heart attack.
• Ischemia modified albumin (IMA): high level of IMA indicate ischemia.
• B-type natriuretic peptide test: natriuretic peptide (NP) test is a blood test that measures levels of a protein called BPN that is made by the heart and blood vessels. NP levels are higher than normal in cases of heart failure. Normal value : 100 (pg/mL)
• Creatine Kinase (CK): diagnosis for acute MI, elevated level of CK diagnose myocardial infraction. Normal value : <150 units/L

• C-reactive protein (CRP): CRP is a marker for inflammation, and atherosclerosis has an inflammatory component.
• Patients with elevated levels of CRP have an increased risk for heart attack, stroke, sudden death, and vascular disease.
• CRP levels less than 1: lower risk
• CRP levels of 1 to 3: intermediate risk
• CRP greater than 3: highest risk
• Lipoprotein phospholipase A2 (Lp-PLA2): Elevations in the levels of Lp-PLA2 indicate greater risk of plaque formation and greater risk of cardiac events.

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SERUM LIPIDS

• Measurement of total cholesterol:

A lipoprotein panel is a blood test that can help show whether you are at risk for coronary heart disease (CHD).

* Total cholesterol, LDL (“bad”) cholesterol, HDL (“good”) cholesterol. Triglycerides- Triglycerides are a type of fat in your blood.

* A lipoprotein panel measures the levels of LDL and HDL cholesterol and triglycerides in blood. Abnormal cholesterol and triglyceride levels may be signs of increased risk of CHD.

* Need to fast for 9 to 12 hours before a lipoprotein panel.

HEART FUNCTION TEST

• Electrocardiogram (ECG): An ECG is a cardiac screening test that should be done on everyone on their first visit to a cardiologist.
• An EKG establishes baseline information about the structure of heart, its electrical conduction patterns and possible arrhythmias.
• Echocardiogram: An echocardiogram is a noninvasive ultrasound cardiac screening test that records specific geographical areas of the beating heart, which reveals blood flow patterns and allows us to measure size and wall thickness of the heart’s chambers.
• Exercise/ Nuclear stress test: An exercise stress heart test is ordered to assess how heart is functioning when heart rate and blood pressure are increased during physical exertion.

LIVER FUNCTION TEST

• Laboratory test for Liver This group of test indirectly assesses the health of liver cells by measuring enzymes arising from the cells and also assesses substances produced by the liver and used elsewhere in the body.
• If the liver enzymes are raised it can suggest damage to liver cells such as occurs with chronic alcoholism or with certain viral infections such as viral hepatitis.
• Some common liver function test include:
• 1. Alanine Transaminase test (ALT) ALT is used by our body to metabolize protein. If the liver is damaged or not functioning properly, ALT is released into the blood. This causes ALT levels to increase. A high result on this test can be a sign of liver damage.
• 2. Aspartate Transaminase test (AST) AST is an enzyme found in several parts of our body. Since AST levels aren’t specific for liver damage, it’s usually measured together with ALT to check for liver problems, when the liver is damaged, AST is released into the bloodstream. A high result on an AST test might indicate a problem with the liver or muscles.

LFTs Contd

•  Alkaline Phosphatase test (ALP) An ALP test is typically ordered in combination with several other tests. High levels of ALP may indicate liver damage, blockage of the bile ducts, or a bone disease.
• Albumin test Albumin is the main protein made by your liver. An albumin test measure the function of the liver. A low result on indicates abnormal function.
• Bilirubin test Bilirubin is a waste product ordinarily processed by the liver. A damaged liver can’t properly process bilirubin. This leads to an abnormally high level of bilirubin in the blood. A high result on the bilirubin test indicates that the liver isn’t functioning properly.

KIDNEY FUNCTION TEST

• Laboratory test for Kidney
• Urea clearance test: the urea clearance test requires a blood sample to measure the amount of urea in the blood stream and two urine specimens, collected one hour apart, to determine the amount of urea that is filtered, or cleared, by the kidneys into the urine.
• Urine osmolality test: Urine osmolality is a measurement of the number of dissolved particles in urine. The test may be done on a urine sample collected first thing in the morning, on multiple time samples, or on a cumulative sample collected over a 24-hour period.
• Blood urea nitrogen test (BUN): the BUN test measures the amount of nitrogen contained in the urea. High BUN levels can indicate kidney dysfunction, but because BUN is also affected by protein intake and liver function, the test is usually done together with a blood creatinine, a more specific indicator of kidney function.

Kidney function test

• Creatinine clearance test: With normal kidney function, the amount of creatinine in the blood remains relatively constant and normal, an elevated blood creatinine level is a more sensitive indicator of impaired kidney function than the BUN.
• Urine albumin: Healthy kidneys have filters (nephrons). These remove wastes but keep in large cells, like red blood cells and proteins. Albumin is one type of protein. When the filters are damaged, they may leak protein into your urine. Albumin levels can go up if you exercise a lot or have high blood sugar, too. Bladder infections can also make the levels go up.
• electrolytes: Measurement of the blood levels of other elements regulated in part by the kidneys can also be useful in evaluating kidney function. These include sodium, potassium, carbon dioxide bicarbonate, calcium, magnesium, phosphorous, protein, uric acid and glucose.

• Sodium 35-145 mmol/L usually caused by excess water (e.g., serum antidiuretic hormone) and is treated with water restriction. in severe dehydration, diabetes insipidus, significant renal and GI losses.
• Potassium 3.5-5 mmol/L with renal dysfunction, acidosis, K-sparing diuretics, hemolysis, burn, crush, injuries by diuretics, or with alkaloids, severe vomiting and diarrhea.
• CO2 22-28 mmol/L Sum of HCO3 and dissolved CO2. Reflects acid-base balance and compensatory pulmonary (CO2) and renal (HCO3-)
• Calcium 8.5-10.5 mg/dL with hyperparathyroidism, paget disease, bone tumor, increased absorption from bone to ECF, decrease neuromuscular activity with dietary deficiency, increased excretion, pancreatitis, hypoparathyroidism, rickets, osteomalacia, renal insufficiency Typical reference ranges for healthy adults are:

• Chloride 98-106 mEq/L dehydration, multiple myeloma, kidney disorders, adrenal gland function
• Phosphorus 2.4-4.1 mg/dL kidney and parathyroid gland dysfunction Lab result Normal value Serum creatinine Women 0.6-1.1 mg/dL Men 0.7-1.3 mg/dL
• Creatinine clearance Women 88-128 mL/min Men 97-137 mL/min Urine albumin 0-8 mg/dL BUN 7-20 mg/dL Urine microalbumin <30 mg (30-300 mg may mean early CKD, more than 300 mg may mean a later stage CKD Albumin to Creatinine ratio <30 mg/gram

BLOOD GLUCOSE

OGTT

BLOOD GLUCOSE TEST

THYROID FUNCTION TEST

• Vitamin D Normal range: 30 to 74 ng/mL 25-hydroxy vitamin D When calcium is low and/or a person has symptoms of vitamin D deficiency, such as bone malformation in children (rickets) and bone weakness, softness, or fracture in adults (osteomalacia),
• 25-hydroxyvitamin D usually is ordered to identify a possible deficiency in vitamin D. 1,25-dihydroxyvitamin D This testing may be ordered when kidney disease or abnormalities of the enzyme that converts 25-hydroxyvitamin D to 1,25-dihydroxyvitamin D is suspected.
• Rarely, this test may be done when calcium is high or a person has a disease that might produce excess amounts of vitamin D, such as sarcoidosis or some forms of lymphoma (because immune cells may make 1,25-dihydroxyvitamin D).

LUNG FUNCTION TEST

• Transtracheal mucus cultures (rarely done). Transtracheal sputum cultures are tests performed on a mucus sample obtained directly from your windpipe (trachea).
• Lung biopsy. A lung biopsy is a test done on a very small piece of lung tissue to look for conditions such as lung cancer or fibrous tissue in the lungs
• Thoracentesis. Thoracentesis involves puncturing the chest wall to obtain fluid from the space around the lungs. Fluid obtained during the test can be checked for signs of infection or cancer.
• Computed tomography (CT) scan.

OTHERs

• Serum Amylase- this is commonly ordered in cases of abdominal pain to see if the pancrease gland is inflamed or its duct obstructed.
• Follicle stimulating hormone (FSH)- Sustained high levels of FSH in a women can indicate that the menopause is approaching or has happened. Normal level: 5-20 mlU/ml
• Progesterone level – progesterone measurements are often used to determine if ovulation has occurred. The ovaries produce very small amounts of progesterone until ovulation happens. Normal level- 3ng/mL

• Beta Human Chronic Gonadotropin (HCG)- this is the hormone produced in early pregnancy and is the basis of the urine pregnancy tests. An HCG level of less than 5 mIU/mL is considered negative for pregnancy, and anything above 25 mIU/mL is considered positive for pregnancy.
• Prolactin - is a pituitary hormone that stimulates and sustains milk production in nursing mothers. Prolactin levels are usually normal, Some women with PCOS do have elevated prolactin levels

AUTOIMMUNE TEST

DRUG ASSAYS

The level of certain drugs can be measured in the serum.

The commonly performed drug assays are usually those where the drug has a fine line between being toxic and therapeutic.

The common assays include:

- Serum digoxin

- Serum phenytoin

- Serum theophylline

TUMOR MARKERS

• PSA (prostate specific antigen) test which is monitored in prostate cancer.
• The AFP (alpha foeto-protein) is another-used for monitoring treatment for liver cancer.
• Ca-125, is used to monitor progress in ovarian cancer.
• Tissue histology: FNA = Fine needle aspiration- A fine needle on a syringe is inserted into a lesion and negative pressure is applied to suck up some cells for microscopy. This is usually to check for tumor cells.
• Excision Biopsy- this is where an entire lesion is removed and sliced up into thin sections for microscopy.

BIOPSY/SWAB/CULTURE

•  Biopsy- this is where a small part of a lesion is removed for microscopy to try and make a diagnosis
• Microbiology- any moist area on the body can be swabbed with a sterile cotton tipped bud, plated out on to agar jelly plates and placed into an incubator to see if bacteria will grow from swab. Once the bacteria have grown they can be identified under the microscope and tested to for sensitivity test (C& S).
• Scrapings of tissue or cuttings of nails can be similarly treated for fungal lesions.
• If there is a delay between taking the swab and plating it out, it has to stored in special transport media.
• Sputum is commonly cultured for bacteria causing bronchitis, pneumonia and tuberculosis.
• Faeces can be cultured for bacterial, viral and parasitic organisms.
• Cytology- Cytology involves obtaining a normal tissue fluid and examining it under the microscope for early signs of cancer cells.

STI

• Sexually Transmitted Disease (STD) Blood Tests
• VDRL/TPHA- these are screening tests for syphilis.
• HIV- this is a screening test for the presence of Human Immunodeficiency Virus antibody.
• Herpes antibodies- can be measured to assess past or present herpes simplex infection.
• Hepatitis antibody- and antigen testing can be included in the STD tests as well as with Liver Function Tests. The various types of hepatitis can be contracted by other means as well as sexual transmission.

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