An Introduction to Medical Laboratory Science Quiz

Answer: Bilirubin

A CBC/FBC is an important test in diagnosis as it gives a lot of information on a range of haematology parameters. It is not a definitive test, as abnormal results require further testing, but it is an excellent starting point for laboratory diagnosis. Abnormal results include (but are not limited to) a wide array of conditions, including anemia, infection and leukemia

Specifically, this test measures the following parameters quantitatively:
Erythrocytes - red blood cells which carry oxygen to cells.
Leucocytes - white blood cells that fight infection (and the subtypes of this type of cell)
Haemoglobin - the oxygen-carrying protein in erythrocytes
Platelets - small cells that help blood clot

Sometimes a blood film is prepared so a scientist can see the morphology of each type of blood cell. A complete blood count can show abnormal increases or decreases in cell counts. Those changes might be suggestive of a medical condition that calls for more testing. For example, if one of the parameters, haemoglobin, is less than 130 g/L, this is suggestive of anaemia but does not tell us what type of anaemia the patient has. The most common form of anaemia is iron deficiency. If other parameters measured within the CBC suggest this type of anaemia, iron studies testing will be ordered, which include serum iron, ferritin and transferrin.

Answer: Increased Urea (BUN)

The seven parts of a basic metabolic panel (sometimes known as a CHEM-7 or SMA-7) are
four electrolytes: sodium (Na+), potassium (K+), chloride (symbol can't be reproduced), bicarbonate (HCO3-) or (CO2), urea (blood urea nitrogen in the U.S), creatinine, and glucose. Sometimes, a fifth electrolyte, (calcium (Ca2+) is added to the panel.

Taken as a whole, this panel is used as a marker (or lack) of homeostasis (the normal balance of the body's chemical composition). It can diagnose acute conditions that require urgent and specific medical treatment, such as dehydration, diabetic shock from either ketoacidosis, hyperglycemia or hypoglycemia, congestive heart failure, and kidney failure. Specifically, the Urea/BUN and creatinine markers are surrogate tests for kidney disease.

A BUN test measures the amount of urea nitrogen that's in your blood. When your body needs to excrete nitrogen from the breakdown of proteins, it forms ammonia ions, which are toxic to the body. These ions combine with carbon and oxygen to form urea (pictured), which is non-toxic and a waste product. The kidneys filter out urea, and it is passed in the urine. When the kidneys are not working properly, the urea levels rise.

Creatinine is a waste product of muscle metabolism, excreted via the kidneys. However, serum creatinine level is higher in individuals with larger skeletal muscle mass. A raised creatinine level is also an indicator of kidney dysfunction. Because of variations associated with muscle mass, a calculated parameter, the Estimated Glomerular Filtration Rate (eGFR), is used to assess kidney function. It is based on a patient's serum creatinine level, taking into consideration age, sex and race.
As the serum creatinine rises, the eGFR will decrease, indicating decreasing kidney function. The eGFR is a more accurate marker of the severity of kidney disease than urea/BUN.

Answer: Bilirubin

Liver function tests collectively provide insight into hepatic disease. Some tests demonstrate the liver performing its normal functions of producing proteins and expelling bilirubin, a waste product. Other tests measure enzymes that liver cells release in response to damage or disease. Together they screen for liver disease, such as infections (hepatitis), monitor the progression of a disease, eg alcoholic hepatitis and determine serious liver disease, such as scarring found in cirrhosis.

Liver function tests include four enzymes: alanine transaminase (ALT), alkaline phosphatase (ALP), gamma-glutamyltransferase (GGT), and L-lactate dehydrogenase (LDH). Elevated ALP is also found in bone disease, and LD is elevated in several types of tissue damage, but collectively, these four parameters help determine overall liver damage. They are released in high numbers when liver tissue is damaged, but more specific tests are needed to pinpoint specific liver pathology.

Albumin and total protein are two more liver function tests: Albumin is the main protein among several proteins made in the liver. Proteins are needed to fight infections, and build, replace or repair tissues and cells of the entire body. Lower levels of albumin and total protein may be a symptom of liver damage or disease. Lower protein levels are also found in renal disease, but examination of other parameters in the panel will determine the organ that is damaged.

Bilirubin is the seventh LFT. It is a pigmented byproduct of the breakdown of red blood cells, which occurs in the spleen, liver, and bone marrow. As it is water insoluble, it binds to albumin and is transported to the liver, where it is re-packaged into water-soluble conjugated bilirubin and excreted in bile, eventually being eliminated from the body through the faeces. When there is liver damage, the bilirubin is not cleared by the liver, and the bilirubin is deposited and accumulated in the tissues, where its pigment causes a yellow discolouration (pictured).

Sometimes, a haematological parameter, prothrombin time (PT) is considered a liver function test, though a raised PT is not specific for liver damage.

Answer: Microscopy

When microbiological examination is required on a sample (eg swab, urine, sputum, blood, bodily fluid), a physician is trying to find the bacteriological cause of a patient's infection. No matter what the sample type, the examination usually consists of three parts: microscopy, culture and sensitivities (antibiotic testing).

When a doctor suspects an infection, he will prescribe an antibiotic. This is empirical therapy - based on experience. This will hopefully cure the patient's infection, even though the cause is unknown. The microbiology process consists of performing microscopy, which informs how to culture the specimen, and finally, when the bacterium is identified from the culture plates, specific antibiotics can be tested to determine which ones are suitable for treatment. Optimally, the doctor will have selected an appropriate one initially, and if not, other therapeutic ones will now be available.

Microscopy of specimens is primarily determined by the Gram Stain. This stain was invented by Danish bacteriologist Hans Christian Gram, who developed the technique in 1884, and the technique is still used well into the 21st century. It divides all bacteria into two large groups: Gram-positive (stained purple by crystal violet) and Gram-negative (stained pinkish-red by safranin or carbol fuchsin). Further, clinically significant bacteria are either spherical (cocci) or rods (bacilli). So, four main groups are classifiable (Gram-positive cocci are further distinguishable by observation of cocci that are clustered or form chains) (pictured). This information is available in minutes after sample receipt in the laboratory and provides the treating doctor with therapeutic options, often before antibiotic therapy has commenced.

Answer: Patient serum is mixed with a sample of donor erythrocytes

When a blood donor donates blood (around 500 mL or a pint), the blood is separated into packed (red) cells and serum. The latter is further broken down into several products and frozen for later distribution. Anticoagulant is added to the packed cells, and the blood can be refrigerated and used for blood donation for the next 35-42 days.

A patient's blood group is determined by antigens on the erythrocytes. The main ones are those in the ABO group. If the cells contain the A antigen, the blood group is A; if the blood contains the B antigen, they have blood group B; if they have both, they are AB, and if they have neither, they are Group O (ie null). There is another group D; if present, they are "Rh+" and if they do not, they are "Rh-. Thus, a person who is AB+ has all three antigens, whereas an O-negative person has none. Importantly, whatever antigens are present on a patient's erythrocytes means they have serum antibodies to the 'missing' antigens. Eg an O-Negative person will have anti-A, anti-B, and anti-D in their serum, whereas an AB+ patient will have none. These antibodies, when they come in contact with blood from another patient with incompatible blood, will 'fight' against the cells they are directed against, causing clumping and, possibly, a transfusion reaction, possibly death. There are many other antigens present on erythrocytes, but these generally cause minor, if any, transfusion reactions.

The basis of blood banking, besides storing blood for donation, is to determine if donor blood is compatible with the patient's blood to ensure a safe transfusion for the patient. This is called a crossmatch. In this laboratory test, patient serum will be mixed with donor erythrocytes. If clumping occurs in one of three different methods, that donor blood cannot be transfused into that patient. This method will also detect reactions due to 'minor' antigens present on the patient's erythrocytes.

When a patient is booked for a procedure that requires transfusions, the crossmatch will be performed before the procedure, and compatible blood will be reserved for that patient's procedure.
If the blood has to be given immediately (eg trauma), type-specific blood will be given if the patient's blood group is known. If not, O-negative blood will be given as it contains no major antigens.

Answer: Flow cytometer

A pathology laboratory receives biopsies, tissue and surgical specimens and even whole organs, seeking a pathological diagnosis. An anatomical pathologist examines the specimens macroscopically and excises small pieces for microscopic examination. The histology laboratory scientist then prepares the specimens by embedding them in paraffin blocks about an inch (2.5 cm) cubed. The solid blocks are then held in place on a microkeratome, which is essentially a very sharp automated knife. Very thin sections (typically 3-5 micrometres) are then cut and mounted on glass slides. The slides are then stained with different stains depending on the suspected condition.

The main stain used is Haematoxylin and Eosin (H&E) (pictured), which is a good general-purpose stain. The hematoxylin stains cell nuclei a purply-blue, and eosin stains the extracellular components and cytoplasm pink. This stain is also good for identifying malignancies within the stained slide. Other stains, like Masson's and PAS, are commonly used. Immunofluorescence and histochemical stains are also used in diagnosis. The series of slides from each specimen is then examined under the microscope to make a diagnosis.

A flow cytometer is a laser-based lab instrument (found in haematology or immunology labs) that detects chemical and physical differences of cells. Lab scientists use it to evaluate (eg count, sort) blood and other body fluids for particular diseases. Flow cytometry can help diagnose several conditions, especially cancers and leukaemias.

Answer: Cervical Cancer

The discipline of cytopathology was founded by George Nicolas Papanicolaou, a Greek physician, in 1928. In this field, initially, exfoliated cells were collected, stained and examined microscopically. This was particularly useful when cells were collected from the cervical endometrium of women 20-65 who were at risk of cervical cancer. The Pap smear or test aims not only to detect cervical cancer but also to detect potentially pre-cancerous changes (called cervical intraepithelial neoplasia [CIN] or cervical dysplasia). When screening is performed regularly, it is a good preventative tool for this type of cancer. The cellular changes, especially in the early stage, are subtle, and scientists working in the field often need to be certified separately for cytopathology.

Other exfoliative-type cytopathology techniques include bronchial brushings for the diagnosis of deep lung lesions. Besides exfoliative methods of cell collection, there is another subdiscipline of cytopathology - intervention techniques. This usually means fine-needle aspiration cytology (FNAC), where a needle is attached to a syringe to collect cells from lesions or masses in situ.

Answer: Cerebrospinal Fluid (CSF)

Meningitis is a very severe infection that can cause death quickly unless therapy is started early in the disease process. Babies, young children and, surprisingly, teenagers are the most susceptible. The meninges are the three layers that surround the brain. Cerebrospinal fluid washes over the meninges, acting as a cushion and buffer. CSF also surround the spinal column as well providing similar protection. The meninges can become inflamed via infections that spread through blood that seeds the CSF, or the meninges can be infected directly from adjacent anatomical structures. Increased leucocytes and microorganisms are secreted into CSF in meningitis.

The specimen of choice is CSF from lumbar puncture. Unfortunately, it is the most invasive and painful method of all specimen types. The patient must lie on his/her side with their back in a convex shape. A needle must be inserted between the lumbar vertebrae into the spinal cord. This is very difficult to obtain, especially with a baby or small child who is in a lot of pain. Normal CSF is clear and almost free of cells. Cloudy CSF indicates pathology usually due to increased leucocyte numbers and/or bacteria.

Normally, there are no leucocytes (or very few) in CSF. A cell count is the first test performed while the Gram stain is being prepared. If the white cell count is high, a differential slide is prepared. When stained, the scientist can tell what type of leucocyte is increased. In bacterial meningitis, the differential will show an increase in neutrophils both in absolute numbers and proportion of the white cell count. The Gram stain must be examined closely and thoroughly, as bacterial numbers may be very low. Common pathogens found in bacterial meningitis include (but are not limited to):
Streptococcus pneumoniae (Gram positive cocci)
Neisseria meningitidis (Gram positive cocci) [pictured showing intracellular infiltration]
Haemophilus influenzae (Gram negative bacilli)
Streptococcus Group B (Gram positive cocci) [neonates]
Yeast (Candida albicans and Cryptococcus neoformans) [Immunocompromised patients]

Treatment for this severe infection must be both aggressive and commenced early in the disease, not just to aid recovery but also to stop the drastic consequences that can follow acute infection.

Answer: Polymerase Chain Reaction

Viruses are too small to be seen with a light microscope. Diagnostic methods are based on the effects of viruses, which can be subsequently observed.

The traditional detection of viral infection has been viral culture. Specimens (swabs, bodily fluids, CSF) are placed in different cell lines, each line known for the virus being tested for its ability to infect. If these cells show changes in morphology, detectable by a microscope, these changes are known as cytopathic effects, and then the culture is positive. This process takes weeks and is not diagnostically useful for treatment options.

Serologic tests are used to determine if a person has antibodies against a specific pathogen (in this case, a virus) or to detect pathogenic antigens in a patient sample. Detection of antibodies against a pathogen in a patient specimen (blood) indicates exposure to that pathogen. Serologic tests detect one or two or both types of antibodies: immunoglobulin M (IgM) and immunoglobulin G (IgG). IgM positive results indicates that a person is currently or recently infected, while a positive result for IgG and negative result for IgM suggests that the person has been infected or (immunised in the past). This method still takes days, as you need the body to respond to the virus to produce antibodies. Specimens are taken during infection and afterwards in the convalescent phase. The antibody levels in each specimen are compared, and higher IgG levels in the convalescent specimen suggest infection, not previous exposure. Serology is a good diagnostic tool, but it does not inform treatment options.

Molecular techniques (ie viral nucleic acid) are the most specific and sensitive tests for diagnostic virology. They detect either the whole viral genome or, more likely, a segment of the viral genome. In time, they have become cheaper, faster and more automated; they are now considered the primary diagnostic tool for viral infections. They are also used for monitoring viral treatment in infected patients. The most effective nucleic acid technique is the polymerase chain reaction (pictured), which can detect both viral DNA and RNA. This method makes many copies of the virus nucleic acid using virus-specific probes. Real-time PCR is now possible and can detect multiple viruses in one sample in timeframes of less than an hour. This means that not only is diagnosis rapid, it also, for the first time, informs treatment options.

Answer: Urinary glucose dipstick

In type I diabetes, patients do not produce enough insulin to reduce blood sugar (glucose) levels and need lifelong IV insulin injections. Type II diabetes is acquired and is due to the body's ineffective use of insulin or the pancreas not producing enough insulin. Some people are genetically predisposed, but lifestyle factors such as overweight, inactivity, and poor diet significantly increase the risk. It is an insidious disease, often undetected, and the subsequent pathological effects on the body can be devastating.

A urinary dipstick is used mainly in physicians' offices as a screening tool. It usually consists of a series of small patches, each screening for a particular indicator of disease. The dipstick is dipped into a urine sample (non-invasive specimen, easily obtained). Glucose is one of those indicators. Glucose is normally absent in the non-diabetic patient. A positive urinary glucose means further testing is required. It does not give a diagnosis of diabetes.

A random blood sugar (glucose) test with a glucose level of 11.1 mmol/L (200 mg/dL) or higher is suggestive of diabetes. A fasting (8 hours) sample is preferred. In this test the following results indicate:
Less than 5.6 mmol/L (100 mg/dL) is healthy, no diabetes.
5.6 to 6.9 mmol/L (100 to 125 mg/dL) is prediabetes (a warning - lifestyle changes are indicated).
7 mmol/L (126 mg/dL) or higher on two tests is diagnostic for diabetes.

With the oral glucose tolerance test, a baseline fasting glucose level is taken, then a liquid containing 75g of glucose is drunk. Subsequent blood samples are taken over two hours to test blood sugar levels. An initial rise in glucose levels after one hour should be followed by a significant drop in glucose levels after the two-hour post-sample:

Less than 7.8 mmol/L (140 mg/dL) after two hours is healthy.
7.8 mmol/L and 11.0 mmol/L (140 to 199 mg/dL ) suggest prediabetes.
200 mg/dL (11.1 mmol/L) or higher after two hours is diagnostic for diabetes.

The glycated or glycosylated haemoglobin test most often diagnoses type II diabetes. Also called the A1C test, it measures the amount of haemoglobin that has glucose molecules attached. It reflects the average blood glucose level for the past two to three months:
Below 5.7% is healthy.
5.7% to 6.4% is prediabetes.
6.5% or higher on two separate occasions is diagnostic of diabetes. This test is also used to monitor the control of diabetes. Diabetic patients should aim to keep levels below 7% according to the American and Australian Diabetes Associations.
(Note: Reference ranges may differ slightly from country to country).