CLINICAL CHEMISTRY

Welcome to the Clinical Laboratory

Clinical Chemistry

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Clinical chemistry is the department in the lab where pure chemistry meets up with disease and clinical diagnosis. An example would be electrolyte levels in blood.

Clinical chemistry is most likely the largest department in any laboratory as well as the most automated.  

Clinical chemistry measures levels of chemical components in body fluids. These chemicals are called biochemicals.

Types of Measurements in Chemistry

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Qualitative measurement relies on words (some, many, none, pale) to tell us quality. The liver enzymes are high.

Quantitative measurement relies primarily on numbers as the main unit of analysis. The blood glucose is 100mg/ml.

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Biochemicals measured may include blood glucose, electrolytes, enzymes, hormones, lipids (fats), other metabolic substances, and proteins.

The results of these measurements is quantitative, meaning there will be numbers involved stating “how much.” We’ve mentioned this before in another PowerPoint,

but, would the doctor have a more accurate picture of health with an answer like, “an elevated BUN” or “the BUN result is 2.4mg/dl”?

Examples of Measuring Biochemicals:

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Blood glucose, or blood sugar levels indicate how the body handles glucose. Measuring glucose levels after fasting can help

diagnose diabetes or hypoglycemia (low blood sugar).Cardiac enzyme levels indicate the health of

heart muscles. Measuring cardiac enzymes can help the doctor

determine if the patient has had a heart attack, when the episode occurred and how severe it was.

Types of Specimens used in Clinical Chemistry

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Tests in clinical chemistry are performed primarily on serum, plasma, urine and other body fluids. Serum is the yellow watery part of blood that is left

after blood has clotted and all blood cells have been removed.

Plasma is in essence the same as serum, but is in blood which hasn’t clotting. Plasma is obtained by centrifugation before clotting occurs.

Both look similar and can easily be visually confused.

Clinical Chemistry is Sometimes Called Analytical Chemistry

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An analyte is the chemical in the blood that we want to test for.

A solvent is the liquid in which the analyte is dissolved (serum, plasma, urine, spinal fluid or CSF).

Analyte + Solvent = Solution. The solution being tested in chemistry is

either serum, plasma, or other body fluid in which an analyte is dissolved.

Reagents used in Clinical Chemistry

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Reagents -substances that are employed to produce a chemical reaction when coupled with other substances.

Preparation of any reagent, control, standard or chemical requires precision and accuracy

Depending on the instrumentation, reagents come in several forms: liquid, dry, cartridge, strip.  

Any reagent that is prepared must be labeled with date/time of preparation, concentration.

Standards - Different Than Reagents

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The greatest portion of chemistry testing is quantitative analysis - testing results in a number. qualitative testing results in positive/negative,

plus/minus, yes/no results. (the 'n' in quantitative means 'number'.)

Standards are purified chemicals that have known and exact values. They are used to calibrate instruments.

Ordering Tests in Clinical Chemistry

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Large chemistry labs receive orders for hundreds of different tests

But few labs do all the tests orderedTests not done in these smaller labs are sent

to reference labs to be run in much larger batches

Ordering Tests in Chemistry

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Tests that are done right in the hospital lab are sometimes categorized as general or routine tests.

These tests can be ordered individually as single tests or they are categorized as panels. Panels are sets of tests grouped to look at problems in body systems. These are the same systems you studied in A&P.

Two Most General Screening Panels

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Basic Metabolic Panel: serves as an initial broad medical screening tool of kidney, liver function, and electrolyte and fluid balance

Comprehensive Metabolic Panel: same as BMP, but more tests are included, maybe thyroid, calcium or alkaline phosphatase.

These tests are used to screen general health of a patient. They aren’t used to follow the course

of disease and treatment.

Panels of Tests in Chemistry

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As you can see, these panels are diagnostic tools for many different body systems.

Problems with the renal system would an example of a finding of these panels.

Electrolyte Panel

Electrolyte Panel: may include sodium, potassium, chloride, CO2. Measuring electrolytes can specifically indicate certain metabolic and kidney disorders. Kidneys help balance acids and bases in the body.

While it may be helpful to the doctor to know the specific CO2 level of a patient, the other tests in an electrolyte panel work together to give a picture of acid-base balance and hydration status of the patient. Can you see why electrolytes are affected by kidney function?

Electrolytes (cont.)

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And as you might guess from their name, electrolytes are electrically charged, which means that they can conduct electrical impulses. The body needs electrical impulses to make muscle cells contract. So, severe imbalance of electrolytes is a very dangerous thing. A common cause of such a degree of electrolyte imbalance is dehydration. (Drink your water!)

Kidney Function Panel

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Kidney Function Panel: BUN* and Creatinine to assess function of kidneys. Both are waste products excreted by the kidneys. If a BUN test reveals that your urea nitrogen levels

are higher than normal, it probably indicates that your kidneys aren't working properly. The same is true for the creatinine test – high levels show poor kidney function.

BUN* is actually an acronym for Blood Urea Nitrogen. It isn’t pronounced bun, like hamburger bun, but B.U.N.

Lipid Panel

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Lipid Panel: lipids are fats in the body. This panel gives a profile of Total Cholesterol, HDL-cholesterol (good cholesterol), LDL-cholesterol (bad cholesterol), and triglycerides (fats). Lippoproteins transport cholesterol, triglycerides, HDL, LDL

and VLDL, which are predictors of heart disease. A patient can feel perfectly healthy but have a high risk for cardiac problems if they have high levels of some of these lipoproteins.

HDL carries cholesterol from the tissues to the liver to be excreted. So high levels of HDL are good.

LDL carries cholesterol too, but deposits the cholesterol in blood vessels. This increases the risk for strokes and heart attacks.

Plaque deposits

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You can see why it’s good to know lipid levels when you see what plaque does to a vessel. Which cholesterol type deposits plaque in the vessels?

Thyroid Panel

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Thyroid Panel: to help evaluate thyroid function and diagnose thyroid disease. Commonly includes TSH, T4, T3

The thyroid gland is an important organ that regulates body metabolism. It is located in the front of the neck just below the voice box. It secretes two main thyroid hormones – thyroxine (T4)

and triiodothyronine (T3). These hormones allow the body to use energy. If you

have too little of these hormones, you have not used the possible energy and are tired.

So, if the mechanisms are working badly, patient is feeling tired, they could be suffering from hypothyroidism.

The Thyroid and Pituatary Glands

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Together these two glands work to regulate metabolism. So, if the patient is always tired, a Thyroid Panel may be ordered to assess hormone levels.

Enzyme Panels

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Enzymes Panel – enzymes are in all cells. Enzymes are released into the blood by organs that are damaged or diseased. The type of enzyme released can indicate which organ is affected; heart, liver, pancreas, even bone. There are Cardiac Enzyme Panels, Liver Enzyme

Panels, etc., which are measuring the amount of different enzymes released by the particular organ being investigated.

Example of Diagnosis Using Enzyme Testing

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Enzymes tested are often called biomarkersWhen determining if chest pain and related

symptoms are due to heart burn or heart attack, biomarkers are measured

Acute myocardial infarction (AMI), also known as a heart attack, is defined as the death or necrosis of myocardial cells due to prolonged ischemia, often the result of a sudden or severe blockage of blood flow to the heart.

Example of Diagnosis - Cardiac Enzymes

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The diagnosis of cardiac disease and injury is based on a clinical picture that includes physical exam, medical history, ECG, and laboratory testing, including cardiac biomarker monitoring. 

Levels of these cardiac biomarkers are measured at timed intervals. A rise in level of the enzyme indicates damage has occurred.

Beyond Panels to Special or Esoteric Chemistries

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Endocrinology: analysis of hormones and diagnosis of endocrine disorders

Toxicology: the study of drugs of abuse and other chemicals

Therapeutic Drug Monitoring: measurement of therapeutic medications blood levels to optimize dosage

Electrophoresis: Protein studies

Automation in Clinical Chemistry

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Even as late as 1960 most tests performed in the lab were done manually. Reagents were made by the technologists, tests were performed usually singly when needed.

Slowly at first, automation become the driving force within the lab yielding better, faster, improved testing.

Most current laboratories are now highly automated to accommodate the high workload typical of a hospital laboratory. Tests performed are closely monitored and quality controlled.

Common Benefits of Automation Also True for Clinical Chemistry

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Increased number of tests performed by one technologist in a given time period. Labor costs decrease.

Minimized variation in results between technologists due to slight variations in technique.

Smaller amounts of sample/reagents.Increased walk-away capabilities, more multi-tasking

for staffIncreased variety of techniques/tests being offered;

improved patient care as a result 

Testing by Manual Methods

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Manual means making the reagents and performing the test by hand.

Definitely slowDefinitely labor intensiveOften not precise

Automated Chemistry Lab

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Automation in the Clinical Chemistry Lab

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Automated analyzers merely incorporate the methods previously used in manual methods for chemical analysis.

Students in Med Tech or MLT programs learn these manual methods to gain deeper understanding of the automated instruments they will be using in the labs they work in.

Types of Manual Methods Used in Automation

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Spectrophotometer

Electrophoresis

Ion Selective Electrode

This automated instrument uses all the methods on the right.

Spectrophotometry

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Spectrophotometry– analytical techniques to measure the light absorbed (or transmitted) by a colored solution at a particular wavelength; dependent upon two things - color and intensity Example: An automated chemistry analyzer adds reagent

(colored solution) to specimen (containing the chemical to be measured) and with spectrophotometry, measures concentration of color. This tells us how much chemical is in the specimen (ex. how high the glucose is.)

Electrochemistry

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Electrochemistry - study of chemical reactions occurring because of the flow or presence of electrons between two dissimilar substances; employs current and electrical reaction. Example: Electrophoresis– process of measuring

migration of charged solutes/particles (usually proteins) in an electrical field. Sometimes this is done by automated

electrophoresis sometimes the process is

Ion Selective Electrode

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Ion Selective Electrode (ISE)- potentiometric method measures movement of electrical, free ions. Common measurement for sodium (Na), potassium (K), and chloride (Cl).

Example: analyzing electrolyte levels Or, the most common example in all labs is the pH Meter

Mass Spectrophotometry

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Simply put, mass spectrophotometry identifies the masses of the molecules making up a sample of material. This isn’t a kicked up spectrophotometer – it works differently.

It is used for determining the elemental composition of a sample, and for clarifying the chemical structures of molecules.

Often used in toxicologyExample: A new innovation in mass spec is a portable

instrument which can measure chemicals in the environment (on the street) giving quick results. Can you imagine the possibilities of using such an instrument to keep the population safe?

One Next to Last Thought

All the automated instruments in the clinical lab, and particularly in chemistry, require maintenance and repair. People who do this type of repair are often MLTs or MTs who enjoy tinkering with things. Instrument repair is a lucrative job!

Review Questions

What type of specimens are used for testing in chemistry?

Define analyte and solvent.What are standards used for in chemistry?Name two types of manual testing that has been

upgraded and is used in automation.Panels test systems. True or falseIf enzymes are found in all cells, why do we assay

for high levels?What tests in chemistry will indicate that the

patient is dehydrated?