The Uses of Urinalysis

Use the information from this sheet as well as any other reliable sources available to answer the following questions. Urinalysis is the topic.

You can tell a lot about someone from their urine! Since the days of ancient Greece, physicians have used the appearance, smell, and even taste of urine to diagnose disease. Nowadays, more sophisticated chemical tests are available that can detect hormones and drugs in the urine, even at very low levels.

Urine is made by the kidneys. We will study the kidneys in greater detail in Module 8, but in this case study we will investigate their role in two physiologically important concepts: homeostasis and mass balance. The kidneys produce urine in three steps: first, blood is filtered into the lumen of the kidney tubules. Any substance that is small enough to fit through the filter will end up in the kidney tubules, and that ends up being virtually everything in the blood except for cells and proteins.

After filtration has occurred, substances that the body wants to retain may be re-absorbed back into the blood from the kidney tubules. For example, in a healthy person, all the glucose that ends up in the kidney tubules will be reabsorbed into the blood by transporter proteins. However, in a person with uncontrolled diabetes mellitus, levels of blood glucose may be so high that all of the transporter proteins become occupied, and some glucose may remain in the urine.

The third component of urine production is the selective secretion of various substances into the urine with the help of transporter proteins. Drugs, and other chemicals are typically secreted into the urine by the kidneys to clear them from the system more rapidly than they would be just by filtration alone. In addition, the kidneys use secretion to regulate the volume, osmolarity, and pH of blood by regulating the amount of water, salt, and hydrogen ions in the urine. In Chapter 19, your book describes a particular challenge presented by the kidneys when the antibiotic penicillin was first used to treat bacterial illnesses. In the 1930s, penicillin production was difficult and slow, and doctors found that when they gave it to patients, it was cleared from the blood rapidly by a kidney transporter protein called the Organic Anion Transporter (OAT). Initially, doctors circumvented this problem with the resourceful but unpleasant strategy of collecting urine from penicillin-treated patients and re-extracting the drug from the collected urine! Later, a synthetic compound called probenecid was developed that decreased the rate at which penicillin was secreted into urine because it also used the OAT transporter, and was thus able to "compete" for OAT binding with penicillin.

Urinalysis Questions

1. Many employers require employees to submit to urine tests for recreational drugs as a condition of employment. As a consequence, there is a substantial body of information on the internet about strategies and products that can be used to "fool" a urine drug test. List three ways such a strategy or product might work. Then discuss whether drug test manufacturers or administrators would be able to adapt their tests to detect that type of cheating.

2. Although untreated diabetes mellitus results in glucose being found in the urine, diabetes is most commonly diagnosed with a blood test. In contrast, home pregnancy tests, which detect the hormone Human Chorionic Gonadotropin, which is found at high levels in the blood of pregnant women, are given as urine tests. Compare the use of blood and urine tests in clinical diagnosis.

3. Meghan is really hungry, but doesn't have time to eat lunch, so she stops at a convenience store to buy a large bag of potato chips that she can consume while driving. What will be the immediate effect on Meghan's blood osmolarity? How will her body regulate the osmolarity of her blood? Would her body do anything differently if she also purchased a 64-ounce diet soda to drink while she ate her chips?