Kidney Functions Tests, UTI and AKI

Question 1

What is blood urea nitrogen? How is it measured?

Answer 1

• BUN is the nitrogen content of urea in the blood and has a molecular weight of 28
• Normal amount is between 8 and 30mg/dl

Question 2

Where and how is urea made?

Answer 2

All amino acids in the body have a nitrogen-carbon-carbon backbone. The amino acids can be deaminated usually occurring in the liver. This creates ammonia or NH3 (toxic to body). The liver adds a carbon to the ammonia to create urea and can be excreted through urine.

Question 3

Give examples of things that can make urea high or low

Answer 3

• Acute kidney injury (AKI) and chronic kidney disease (CKD) = increase
• anything that increases protein breakdown = increase
• Elevated corticosteroids= increase
• diet high in protein = increase
• Liver failure = decrease

Question 4

What is phosphocreatine, creatine and creatinine?

Answer 4

• Phosphocreatine: creatine molecule with phosphate group stored inside muscle cells and brain cells (creates creatinine)
• creatine: involved in energy and muscle contractions (creates creatinine)
• Creatinine: constantly released from muscle cells to enter the blood

Question 5

What are things that would make serum creatinine rise or drop?

Answer 5

• Acute kidney injury (AKI) and chronic kidney disease (CKD) = increase
• Drugs cimetidine(H-2 blocker) and trimethoprim(antibiotic) = increase
• Low muscle mass =decrease
• Low protein diet = decrease

Question 6

How is creatinine used to estimate GFR?

Answer 6

Kidney function = normal serum creatinine/ current serum creatinine

*normal serum creatinine is 1mg/dl

Question 7

What is a Urinary Tract Infection and define the terms cystitis and pyelonephritis?

Answer 7

Infections in the urinary tract

Question 8

Recall the mechanisms that work to fend off microbes and infections that may cause UTIs

Answer 8

• Washout phenomenon: peeing washes pathogens out
• Local immunity: IgA and neutrophils help remove bacteria’s that cause UTIs
• Mucin layer: epithelial cells lining the bladder secrete substances and cling to bladder wall. Prevents colonization of bacteria
• Vaginal flora: Lactobacillus generates lactic acid to lower pH of urine-> toxic to pathogens
• Prostate secretions: zinc ions prevent the bacterial attachment

Question 9

Recall risk factors for developing a UTI

Answer 9

• Females: less estrogen to create mucin layer, shorter urethra, contraceptives
• Elderly: dehydration and decreased immune response
• Urinary catheterization: if in for long periods it may cause biofilms and can cause gram (-) septicemia
• Diabetes: unabsorbed glucose remains in filtrate and bacteria feed off it

Question 10

Recall definitions for vesicoureteral reflux and urethrovesical reflux (obstruction)

Answer 10

• Vesicoureteral: backflow of urine from the bladder into the ureter. If urine has bacteria could cause UTI
• Urethrovesical: backflow of urine from the urethra into the bladder. Squatting or coughing could cause this

Question 11

What is the difference between complicated and uncomplicated UTIs?

Answer 11

• Complicated: occurs in those with risk factors (pregnant, postmenopausal, men w BPH)
• Uncomplicated: might occur in a healthy individual (not pregnant, not menopause)

Question 12

Recall the most common uropathogens. Which one is a fungal infection?

Answer 12

Gram(-): E.coli, Enterobacter, Pseudomonas aeruginosa
Gram(+): MRSA, staphylococcus saprophyticus
Candida species: fungal UTIs occurring in hospitals mostly

Question 13

What are biofilms that can with cystitis?

Answer 13

E. coli can stick to catheter and climb back up to the bladder where it creates biofilms-> slimy layers composed of microbial products

Question 14

What are common causes of pyelonephritis?

Answer 14

commonly develops from cystitis or from infection in genitourinary system from septicemia (bacteria gained entry though systemic circulation)

Question 15

Recall the clinical manifestations of cystitis and pyelonephritis

Answer 15

• cystitis: discomfort when peeing, urinary frequency and urgency, hematuria
• pyelonephritis: fever, chills, flank pain, vomiting

Question 16

Describe how urinalysis helps to diagnose a UTI

Answer 16

• Microscopy: reveal pyuria (5 or more WBCs per high power field), hematuria, and epithelia cells
• Dipstick test: detect nitrites and leukocyte esterase. Positive nitrite test means gram (-) bacteria. Leukocyte esterase found in WBC->pyuria

Question 17

How are UTIs treated? Recall the common drugs mentioned in the reading

Answer 17

• trimethoprim/sulfamethoxazole (Bactrim, Septra): combo antibiotics that inhibit bacteria’s ability to produce folate
• ciprofloxacin: inhibition of the bacterial DNA gyrase (helps bacteria replicate)
• phenazopyridine (Pyridium OTC): alleviate the dysuria, irritation, and urinary urgency associated with UTIs (may turn urine orange or red)

Question 18

How is it believed that cranberry juice may help prevent a UTI?

Answer 18

it may resist bacterial attachment to bladder wall.

Question 19

What is an AKI and what are AKIs characterized by?

Answer 19

Acute Kidney Injury: sudden decline in kidney function. Characterized by low GFR, low urine output, and nitrogen buildup

Question 20

Describe Prerenal AKI and what common causes are

Answer 20

• most common
• decrease in blood flow to the kidneys
• Causes: hypovolemia like with severe hemorrhaging, vomiting, diarrhea, big burns, sepsis and anaphylaxis

Question 21

Describe Intrarenal AKI and what common causes are

Answer 21

• internal structures of the kidneys are damaged, due to ischemia, toxins, or tubular obstruction
• causes: acute tubular necrosis (ATN), interstitial nephritis and glomerular nephritis (inflammatory)
• decreased GFR and urine output

Question 22

Describe Postrenal AKI and what common casues are

Answer 22

• obstruction in the urinary tract that is after the kidneys
• most common cause: BPH
• increase pressure and decrease GFR

Question 23

Recall the normal BUN : Creatinine ratio

Answer 23

The normal BUN : Creatinine ratio ranges from [5 – 20] / 1

Question 24

Recall how the BUN : Creatine ratio changes with prerenal AKI.

Answer 24

• low GFR therefore filtrate slow = more absorption of urea = increased BUN
• creatinine is up
• ration increased

Question 25

Why would sodium be high in prerenal AKI?

Answer 25

initially low, but begin to rise with the increased tubular damage

Question 26

Why is urine osmolarity high with prerenal AKI?

Answer 26

RAAS activated bc of low BP which increases sodium reabsorption in blood. Water follows sodium and therefore makes urine super concentrated

Question 27

Why does the BUN : Creatine ratio not get really high with intrarenal AKI?

Answer 27

Because cells are dying and can’t reabsorb urea. ratio would be 15:1 or less. Water follows urea out the urine diluting it

Question 28

Why is the urine osmolarity low with intrarenal AKI?

Answer 28

Because the water follows urea out in the urine making it diluted which makes osmolality low.

Question 29

Recall that with early postrenal AKI the lab values look more like prerenal AKI but overtime begin to look like intrarenal AKI