LII:The Comprehensive Guide to Physician Office Laboratory Setup and Operation/Primary laboratory testing domains in the POL

A wide variety of testing may be done in the physician office laboratory (POL), though much of it may be CLIA-waived testing. This chapter talks about the primary testing domains encountered in POLs. These testing domains seem to be relatively common in a POL and offer CLIA-waived tests.

This third chapter on the topic of primary testing domains has six sections.

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3. Primary Laboratory Testing Domains in the POL

Urinalysis

In June 2014, healthcare market research company Kalorama Information estimated that by volume, dipstick urinalysis easily was the most common test type in the POL. Urinalysis' popularity in the POL is in part due to advanced technology, low cost, and high market competition, which have in turn helped make many such in vitro diagnostic (IVD) tests eligible for CLIA's waived category. In fact, more than 1,200 CLIA waivers have been granted for dipstick urinalysis kits alone since 2004. Advances in CLIA-waived benchtop and portable dipstick readers have further improved dipstick interpretation accuracy and increased urinalysis test volumes in the POL.

Another perhaps more important reason for dipstick urinalysis' popularity in the POL is the sheer usefulness of the IVD tool. The College of American Pathologists (CAP) have referred to the urine dipstick as "a remarkable 'lab-on-a-strip'" for its ability to "help detect infection, bleeding, diabetes, and other problems." For example, the pH, specific gravity, and protein prevalence as well as the presence of constituents such as bilirubin, glucose, and nitrites all can aid a physician in ultimately making a solid diagnosis. Even pregnancy can be determined using urine dipsticks specifically designed to detect the hormone human chorionic gonadotropin (hCG).

Basic concepts and collection procedures

The human urinary system is responsible for several tasks, including filtering blood, excreting waste, regulating pH, regulating blood pressure, and creating the hormone erythropoietin, which stimulates red blood cell production in the body. The system is composed of kidneys, ureters, the bladder, and the urethra, all of which play an important role in forming and excreting urine from the body. In short, blood passes through the kidney, and through capillary action much of the liquid of the blood is filtered out and collected, eventually passing through the ureters to the bladder and out the urethra.

When collected properly using quality assurance methods, the expelled urine then has clinical significance when analyzed using physical, chemical, and even microscopic procedures. However, maintaining quality standards is vital, otherwise specimens could become contaminated or reach a state not ideal for testing. Clinical collection procedures encourage mid-stream collection of urine into a sterile, well-labeled container. The contents should be tested within an hour of collection or otherwise rapidly refrigerated. The implementation of standardized terminology, equipment calibration techniques, quality control procedures, and proper reagent storage techniques also help ensure test results and interpretation are as accurate as possible. And of course proper hand, eye, and body protection should be correctly used when handling urine.

Urine composition

Urine is composed predominately of water (95 to 96 percent), with the rest being made up of dissolved organic and inorganic solid waste. When collected over a 24-hour period, the average healthy adult's urine contains approximately 40 to 50 grams of dissolved solid waste. The primary constituents of that waste are, in order of prevalence (assuming a 1,400 mL sample):

• urea, the molecule CO(NH₂)₂ which acts as a primary carrier of waste nitrogen from protein breakdown in the body: 25.0 grams
• chloride, the anion Cl^- which is a vital electrolyte in the blood: 6.3 grams
• sodium, the cation Na⁺ which is vital to osmotic equilibrium in the body: 3.0 grams
• potassium, the cation K⁺ which is vital to proper neuron function and osmotic equilibrium: 1.7 grams
• creatinine, an endogenous byproduct of muscle creatine metabolism: 1.5 grams
• sulfate, the anion SO₄²⁻ which is a byproduct of protein turnover and the metabolism of several sulfur-containing compounds in food and water: 1.4 grams
• dihydrogen phosphate, the anion H₂PO^4- (as a titratable acid) excreted as a byproduct of renal acid-base regulation: 1.2 grams
• ammonium, the cation NH⁴⁺ which is excreted as a byproduct of renal acid-base regulation: 0.8 grams
• amino acids, organic compounds composed of amine (-NH2) and carboxylic acid (-COOH) that are building blocks of proteins: 0.8 grams
• uric acid, the compound C₅H₄N₄O₃ which is a byproduct of the breaking down of substances called purines in the body: 0.7 grams
• calcium, the cation Ca²⁺ which is vital to many functions of human biology: 0.2 grams
• magnesium, the cation Mg²⁺ which is vital to the nucleic acid chemistry of most life: 0.15 grams

Clinical laboratories set reference ranges for these constituents, and when a sample shows one or more of them outside of that reference range, the abnormality is often a sign of an ailment or problem in the body or with a diet. For example, the U.S. National Library of Medicine indicates the normal reference range for urea is 12 to 20 grams (though they also note "normal value ranges may vary slightly among different laboratories"), and numbers outside that range could indicate anything from kidney problems and malnutrition to too much protein in the diet.

Other constituents that normally aren't found in urine in significant quantities (or not at all) can make their way there, and their measurable presence are strong indicators of an underlying illness. Those constituents include:

• bilirubin, a bile pigment resulting from red blood cell breakdown that potentially indicates bile duct blockage, hepatitis, or cirrhosis
• casts, cylindrical particles formed from kidney cell proteins, appear in minute amounts as hyaline in normal samples; the presence of cellular casts containing red and white blood cells indicate a kidney disorder
• crystals, formed from solutes in urine under specific conditions; crystals formed from solutes typical to the healthy individual appear, but the presence of crystals formed from non-typical solutes such as cystine, tyrosine, and leucine potentially indicate illness such as liver disease
• epithelial cells, which line the cavities and surfaces of bodily structures, are normal in tiny amounts; the heavy presence of certain types of these cells in the urine indicate a urinary tract condition such as an infection
• erythrocytes, otherwise known as red blood cells, are a primary oxygen delivery vehicle, and their presence in urine potentially indicates a urinary tract infection or hemorrhage, prostate issues, or cancer of the bladder or kidney
• glucose, a sugar that is typically reabsorbed into blood in the kidney during filtering; its presence could indicate a type of diabetes or alimentary glycosuria
• hemoglobin, a protein found in red blood cells that when found in urine potentially indicate anything from kidney infection to tuberculosis
• ketones, byproducts of fat metabolism that potentially indicate diabetes mellitus or a dietary issue
• leukocytes, otherwise known as white blood cells, protect the body from infectious disease, and their presence (indicated by leukocyte esterase) in urine potentially indicates bladder or kidney infection
• nitrite, the anion NO₂⁻ which appears in urine typically due to endogenous nitrates being converted to nitrites by bacteria, indicating potential bacterial infection
• protein, a building block of life, that when found in large quantities in urine could indicate heart and blood pressure problems, urinary tract problems, or dehydration
• urobilinogen, created from the breakdown of bilirubin, is also potentially indicative of bile duct blockage, hepatitis, or cirrhosis

Testing

The presence of the above constituents — as well as the pH, specific gravity, and clarity of the urine — is determined through visual, chemical, and microscopic laboratory testing. Visual inspections of a urine sample aren't meant to be precise, but the designations of clear, hazy, and cloudy provide a starting point for determining the type and number of constituents in a sample. Later, chemical and microscopic analyses provide more concrete information.

Some constituents like glucose, ketones, nitrites, and proteins are most easily detected through chemical analysis. Others like casts, crystals, epithelial cells, and red and white blood cells are better detected using microscopy. As such, the constituents (or properties) being tested for largely drive the instruments and IVD test kits used. The specific gravity test, for example, can be measured using either a reagent strip or refractometer. The choice of which device to use is most often determined by the CLIA status of a laboratory; a dipstick analysis is largely considered waived testing whereas a refractometer test is non-waived. A similar consideration is made when testing for blood in urine: a chemical-based dipstick test for hemoglobin or a microscopic analysis for the presence of red blood cells can be performed. The dipstick test will likely be CLIA-waived, whereas the microscopic examination is certainly not CLIA-waived. As such, if the highest level of testing done at a POL will be urine dipstick testing, only a CLIA certificate of waiver is needed for the lab; if microscopic urinalysis is to be done, the lab must acquire the next highest level of certification, a provider-performed microscopy (PPM) certificate.

For POLs with only a CLIA certificate of waiver, the primary tools used for urinary analysis will be CLIA-waived urine reagent strips and automated urine analyzers. Express Diagnostics' UrinCheck HealthScreen-10 reagent strips, for example, are CLIA-waived and test for eight of the above mentioned constituents as well as pH and specific gravity. The results are then compared visually with a color-coded guide on the bottle. To avoid color-coded visual inspection, a CLIA-waived urine analyzer like Roche Diagnostics' Urisys 1100 allows associated test reagent strips to be inserted and electronically analyzed, printing out the results.

For POLs with a PPM certificate, CLIA-waived urine reagent strips and analyzers can still be used. However, certified physicians and mid-level practitioners at the lab may also turn to the bright-field or phase contrast microscope to further evaluate urine for constituents that would indicate disease or injury. Bright-filed microscopes are one of the simplest, transmitting white light that gets partially absorbed by the denser parts of the sample, creating contrast. The phase contrast microscope is more complicated, separating the transmitted background light from the light scattered by the specimen to make phase changes more visible. Specimens have to be minimally processed and labile to ensure the accuracy of the test. Microscopic examination is often done reflexively upon confirming abnormal visual and/or chemical results, as suggested by The Clinical and Laboratory Standards Institute. The chemical-based urine reagent strips in some cases can only provide a preliminary diagnosis, requiring microscopy to verify amounts of bacteria or types of crystals in the urine.

Hematology/Blood collection

• hematology concepts

• introduction to blood collection and safety

• theory and collection procedures, including patient prep

• instruments and test kits

• CLIA-waived tests

Chemistry

• chemistry concepts

• instruments and test kits

• CLIA-waived tests

Immunology

• concepts in immunology

• instruments and test kits

• CLIA-waived tests

Microbiology

• common pathogens

• topics in microbiology

• instruments and test kits

• CLIA-waived tests

Toxicology

• topics in toxicology

• instruments and test kits

• CLIA-waived tests