Biomarkers

Renal

1. Discuss the concept of a biomarker

2. Explain how kidney biomarkers can indicate pathologies

3. Discuss the features of an ideal biomarker for estimating kidney function

4. Discuss the importance of kidney function for drug pharmacokinetics

: What are the learning outcomes for the kidney biomarkers lecture? (4 points

1. The nephron is the functional unit of the kidney

2. One nephron filters around 100 microlitres in 24 hours

3. There are around 10⁶ nephrons per kidney

4. Total filtration rate is around 120–130 mL/min

5. Substances enter the tubule if they are small enough

6. Large proteins and cells do not normally pass into the tubule

7. Some substances are reabsorbed passively and/or actively, while some substances are actively excreted into the tubule

8. Water is reabsorbed and urine is formed

What are the key reminder points about the nephron? (8 points)

1. The trafficking of substances through the nephron is known

2. This means the normal qualitative and quantitative composition of urine is also known

3. Deviations from normal urine composition can indicate abnormal physiological processes

4. Urine composition can help detect, diagnose and monitor pathological or pre-pathological states

How can normal urine composition help detect pathology? (4 points)

1. A biomarker is a substance present in a biological fluid

2. Its presence or concentration can indicate a normal or abnormal process

3. Biological samples need suitable biomarkers to detect disease

4. Biomarkers can have functions such as diagnostic, prognostic, pharmacodynamic and predictive roles

5. Biomarkers can have different chemical structures, including proteins, lipids, carbohydrates and ions

What is a biomarker and what functions can biomarkers have? (5 points)

1. Quantifiable

2. Sensitive

3. Specific

4. Linked to the process being observed

5. Inexpensive to test

6. Correlates with clinical outcome

7. Biomarker level changes should correlate with disease progress or seriousness

8. Biomarker variation must be caused by the disease

9. Therapeutic intervention should be monitorable through biomarker levels

10. The test should be practical enough for more clinical settings to perform

What are the features of a perfect biomarker? (10 points)

1. substances in blood can be filtered into urine if they are small enough

2. Urine allows non-invasive analysis compared with blood

3. Relatively large amounts can be collected

4. It is easy to collect, although collection still has practical issues

5. It can detect abnormalities in kidney, prostate and bladder

6. It can also help detect infections, stones, cancers and cardiovascular disease

Why is urine a valuable source of biomarkers? (6 points)

1. Visual inspection gives information on colour

2. Dark colour can indicate dehydration or haemoglobin from inflammation, infection or malignancy

3. Microscopy can show cells or cell debris

4. Microscopy can show yeasts such as Candida

5. Microscopy can show red or white blood cells, which can suggest kidney inflammation

6. Microscopy can show casts and crystal deposits such as oxalate/gout-related crystals

What information can urinalysis provide? (6 points

1. Dipsticks allow quick and cheap analysis of 10 urine parameters

2. They are semiquantitative, giving a range of biomarker concentration

3. They are based on colorimetric tests

4. They require careful dry storage and careful sample collection

5. They often lead to more detailed or specific tests

What are urine dipsticks and how should they be used? (5 points)

1. Leucocytes and nitrites can indicate urinary tract infection

2. Leucocytes are detected by testing esterase activity

3. Leucocytes in urine may indicate pyuria, defined as >10 leucocytes per mL, associated with UTI

4. Nitrites are produced when some bacteria reduce urinary nitrates, and nitrites are not normally present in urine

Q: How do leucocytes and nitrites act as urinary biomarkers? (4 points)

1. Bilirubin and urobilinogen are products of haemoglobin catabolism in the liver

2. They are excreted via the gallbladder

3. Low levels are physiologically present in urine

4. Excessive levels may indicate dysfunction

5. Increased urobilinogen may indicate cirrhosis or viral hepatitis

6. Absence of urobilinogen may indicate obstruction such as gallstones or pancreatic carcinoma

7. Increased bilirubin may indicate cirrhosis or viral/drug-induced hepatitis, and high levels may indicate paracetamol overdose

8. Decreased bilirubin may indicate obstruction, and some antibiotics can prevent urobilinogen formation

What do urobilinogen and bilirubin in urine indicate? (8 points)

1. Normal urine pH is around 5.5–6.5

2. Lower pH values can indicate renal tubular acidosis

3. Values outside the normal range can suggest many diseases and require further investigation

4. High glycosuria with high blood glucose suggests diabetes

5. Glycosuria without high blood glucose may suggest pregnancy-related or renal glycosuria

6. Glucose is normally reabsorbed, but this mechanism can saturate at high levels

7. Ketone bodies may indicate fasting with fever/vomiting, hypoglycaemia in children or uncontrolled insulin-dependent diabetes

: What can urine pH, glucose and ketones indicate? (7 point

1. High protein levels in urine always require more advanced investigation

2. Dipstick protein testing is generic and uses a dye that turns blue in the presence of proteins

3. The test has different sensitivities for different proteins

4. Urine protein levels can vary physiologically with exercise, posture and fever

5. Protein loss in urine may indicate different pathologies

Why are urinary proteins important biomarkers? (5 points)

1. Proteins are filtered through the endothelium and glomerular basement membrane

2. Proteins are normally reabsorbed in the proximal tubule and destroyed, with amino acids returned to blood

3. High molecular weight proteins in urine suggest glomerular proteinuria from damaged basement membrane/glomerulus

4. Examples of high molecular weight proteins include albumin and IgG

5. Low molecular weight proteins in urine can suggest tubular proteinuria from impaired proximal tubule reabsorption/reuse of amino acids

6. Low molecular weight proteins can also cause overflow proteinuria when high blood concentration exceeds reabsorptive capacity

Q: What happens to proteins in the nephron and what types of proteinuria can occur? (6 points)

1. Proteins can be identified by electrophoresis

2. Proteins can also be identified by mass spectrometry

3. Because protein concentration varies, measurements may need to be taken several times over 24 hours

4. Using the protein-to-creatinine ratio allows one measurement only

5. Protein in urine may indicate kidney damage, cardiovascular disease or cancer

6. Haematuria, meaning haemoglobin or red blood cells in urine, can suggest glomerulonephritis or polycystic kidney disease

: How are urinary proteins identified and interpreted clinically? (6 points)

1. Presence of proteins in urine has been linked to malignant conditions

2. NICE includes URO17 for bladder cancer

3. NICE includes ADXBLADDER for bladder cance

How can urine biomarkers be used in cancer detection? (4 points)

1. Kidney function is evaluated by filtration capability

2. Glomerular filtration rate is used to assess filtration

3. Decreased GFR precedes renal failure

4. GFR helps diagnose and monitor CKD progression

5. GFR helps design treatment and monitor treatment effectiveness

Q: Why is assessing kidney function important? (5 points)

1. It should have constant plasma concentration

2. It should not be bound to plasma proteins

3. It should be freely filtered

4. It should not be reabsorbed

5. It should not be excreted/secreted into the tubule

6. It should be easy to detect and quantify

7. The amount filtered equals plasma concentration × GFR

8. GFR can be calculated as: GFR = urinary biomarker concentration × urine volume / plasma biomarker concentration

Q: What makes an ideal biomarker for kidney function and how is GFR calculated from it? (8 points)

1. Creatinine is an endogenous biomarker produced by muscle catabolism

2. Creatinine is easily detected by colorimetric methods

3. Creatinine is filtered and not reabsorbed, but 7–10% is secreted

4. Creatinine varies widely with age, weight, sex and other population factors

5. In advanced kidney disease, creatinine can be produced by microflora overgrowth

6. Cystatin C is another endogenous biomarker and is a 12.8 kDa protein

7. Exogenous biomarkers can be given by infusion or bolus and measured in plasma/urine over time

8. Exogenous options include radiolabelled markers such as ¹²⁵I-iothalamate and ⁵¹Cr-EDTA, and cold biomarkers such as inulin and iohexol

Q: What endogenous and exogenous biomarkers can estimate kidney function? (8 points)

1. The Jaffe test uses picric acid

2. In the presence of picric acid, creatinine forms a yellow derivative

3. Calibration is performed with standard solutions of known creatinine concentration

4. Patient samples are prepared from urine, and the test is straightforward with limited resources

: How is creatinine measured using the Jaffe test? (4 points)

1. Several equations have been developed to link serum creatinine to GFR more reliably

2. These equations aim to improve interpretation of kidney function from serum creatinine levels

Q: How are serum creatinine equations used to estimate GFR? (2 points)

1. The Jaffe test is not specific because other analytes can form Jaffe-like compounds

2. Interfering analytes include some proteins, glucose, ascorbic acid, pyruvate, guanidine and cephalosporins

3. Spectral interference occurs because bilirubin and haemoglobin absorb in the same range

4. Calibration can be unreliable due to co-worker effect/standard preparation issues

5. Creatinine production is affected by age, weight, sex, muscle mass, diet and drugs such as trimethoprim and cimetidine

6. Around 7–10% of creatinine is secreted, so GFR can be overestimated

7. Creatinine can be produced by microflora in advanced kidney disease

8. When GFR is low, creatinine levels are high

9. Normal creatinine levels may still hide poor kidney function

What are the shortcomings of the Jaffe test and creatinine as a biomarker? (9 points)

1. Inulin is a plant polysaccharide made of fructose

2. It is filtered by the kidney

3. It is not secreted

4. It is not reabsorbed

5. It is not metabolised

6. Urine levels do not depend on diet, muscle mass or age

7. It is injected intravenously to maintain steady-state plasma concentration and then measured in urine and plasma

8. It is difficult because quantification needs HPLC, mass spectrometry or enzymatic assays, is invasive, has lower patient acceptability and is lengthy/logistically difficult

Why is inulin a good kidney function biomarker and why is it difficult to use? (8 points)

1. Drug handling should be considered using ADME principles

2. Many drugs are eliminated by the kidney

3. Impaired kidney function reduces drug elimination

4. Reduced elimination can cause high plasma levels, accumulation, toxicity and drug-drug interactions

Why does kidney function matter for drugs? (4 points)

1. Gentamicin is an aminoglycoside antibiotic

2. It is active against Gram-positive and Gram-negative bacteria

3. It is predominantly renally eliminated

4. It can cause reversible nephrotoxicity

5. It can cause ototoxicity

6. It has a narrow therapeutic window

7. Levels below the minimum effective concentration risk ineffective treatment and resistance

8. Levels above the maximum tolerated concentration risk toxicity, and peak-to-valley levels depend on kidney function

: Why is gentamicin important in renal impairment? (8 points)

1. Gentamicin should not fall below the minimum effective concentration

2. Gentamicin should not rise above the maximum tolerated concentration

3. In renal impairment, each peak can build on the previous trough/valley because clearance is reduced

How should gentamicin levels be understood in renal impairment? (3 points)

1. Reduced clearance of active metabolites can cause side effects or toxicity, e.g. morphine glucuronide

2. Low GFR may stop the drug reaching the target tissue, e.g. nitrofurantoin for UTI

3. Some drugs cause direct kidney damage, e.g. methotrexate

4. Some drugs are nephrotoxic, e.g. lithium carbonate

5. Narrow therapeutic window drugs are risky because plasma levels for activity and toxicity are close together

What medicine-related issues can occur when GFR is reduced? (5 points)

because the qualitative/quantitative composition of urine is known

Why can the level of substances in the urine be used to obtain information on physiological processes?

 

because the qualitative/quantitative composition of urine is known

 

because most pathological processes will determine a change in the urine composition

 

because there is no variation of urine composition in the population

 

because it is easy to sample

 

because all the marker of a pathological status appear in the urine

a substance present in a biological fluid whose presence and concentration is an indicator of a biological process

What is a biomarker?

 

an endogenous substance whose presence in a biological fluid indicates a physiological process

 

an endogenous substance whose presence in a biological fluid indicates an abnormal process

 

a substance present in a biological fluid whose presence and concentration is an indicator of a biological process

 

an exogenous substance whose presence in a biological fluid indicates a physiological process

 

an exogenous substance whose presence in a biological fluid indicates an abnormal process

 

A biomarker needs to be linked to the process of interest.

Which of the following is true about a biomarker?

 

) A biomarker is always specific to the process observed

 

A biomarker does not correlate to the clinical outcome of a treatment

 

A biomarker does not need to be quantifiable

 

A biomarker does not allow to estimate the progress of a disease

 

A biomarker needs to be linked to the process of interest.

The colour of the urine can be an indication of abnormal physiological process

What of the following statements about urinalysis is true?

 

Cells are never found in urine

 

A dipstick test only informs on one biomarker

 

The colour of the urine can be an indication of abnormal physiological process

 

Crystal deposits in the urine are caused by bacteria

 

Urinalysis should be carried out at the same time of the day

Dipstick tests can be conclusive for a clinical diagnosis

Which of the following statements about dipstick test is NOT true?

 

Dipstick tests can be conclusive for a clinical diagnosis

 

A dipstick test showing high glycosuria is an indication of diabetes

 

The levels of both white and red blood cells can be estimated with a dipstick test

 

A dipstick test showing values of pH out of the 5.5-6.5 interval should trigger further investigation

 

High levels of bilirubin and urobilinogen may indicate liver or gallbladder disfunctions

High molecular weight proteins are not filtered at the glomerulus if the basal membrane is undamaged

Which of the following statements about proteins in the urine is true?

 

Low molecular weight proteins are filtered at the glomerulus and excreted

 

The level of proteins in the urine does not change with the time of the day

 

After filtration, proteins are destroyed and the amino-acids are eliminated in the urine

 

High levels of low molecular weight proteins is always an indication of high levels in blood

 

High molecular weight proteins are not filtered at the glomerulus if the basal membrane is undamaged

Endogenous biomarkers allow a more reliable estimation of kidney function compared to exogenous biomarkers

Which of the following statements about biomarkers to estimate kidney function is not true?

 

Monitoring the levels of suitable biomarkers in the urine allow to estimate the glomerular filtration rate

 

Exogenous biomarkers to estimated kidney function are used clinically

 

Biomarkers that bind to plasma proteins are not ideal for estimating kidney function

 

Endogenous biomarkers allow a more reliable estimation of kidney function compared to exogenous biomarkers

 

The biomarker should be filtered, not secreted and not reabsorbed

Creatinine is still used as a kidney function biomarker despite its shortcomings

Which of the following statements about creatinine is true?

 

Creatinine is filtered, not secreted and not reabsorbed in the kidney

 

The levels of creatinine in the urine are not affected by the age of the patient

 

Creatinine is not affected by the muscle mass of the patient

 

Creatinine is still used as a kidney function biomarker despite its shortcomings

 

The levels of creatinine in the urine are measured by mass spectroscopy

Kidney play a marginal role in the pharmacokinetic profile of most drugs

Which of the following statements is NOT correct?

 

Poor kidney function can lead to decreased elimination rate of drugs

 

The impact of poor kidney function is not the same for all drugs

 

Kidney play a marginal role in the pharmacokinetic profile of most drugs

 

Kidney play a marginal role in the pharmacokinetic profile of most drugs

 

Poor kidney function affects the elimination of active drug metabolites.