Introduction to kidney tests - Acid-Base metabolism

Question 1

What is GFR based on

Answer 1

• Based on serum-creatinine

Question 2

Sensitivity of GFR to kidney damage

Answer 2

• Poor sensitivity for minor kidney damage

Question 3

When does serum-creatinine start to rise

Answer 3

• 50% flomeruli lost

- Marker of progressive kidney damage

Question 4

plasma creatinine sensitivity - GFR

Answer 4

• Creatinine has poor sensitivity in reference range (clinically silent stage)

Question 5

Hierarchy of kidney function tests (inaccurate to accurate)

Answer 5

• S-urea
• 24h creatinine clearance
• S-creatinine
• eGFR estimated from s-Creatinine
• Direct GFR measurement used for research

Question 6

What is CKD-EPI

Answer 6

CKD-EPI creatinine equation is based on the same four variables as the MDRD Study equation, but uses a 2-slope spline to model the relationship between estimated GFR and serum creatinine, and a different relationship for age, sex and race

Question 7

How does diabetic ketoacidosis cause lower eGFR and increased s-creatinine and urea

Answer 7

• Glycosuria causes an osmotic diuresis
• Decrease in plasma volume
• Dehydrated from loss of fluid in urine
• Due to osmotic diuresis caused by urine glucose
• Decreased blood flow to kidneys
• Decreased glomerular filtration
• eGFR decreased
• s-creatinine and urea increased

Question 8

Hyperkalaemia

Answer 8

• Decreased renal excretion
• Shift of intracellular potassium (due to insulin lack, acidosis, tissue catabolism)
• Total body potassium lower

Question 9

Potassium influences

Answer 9

• Decreased renal excretion
• Re-distribution (shift of intracellular potassium), metabolic acidosis, extracellular h+ exchanged for intracellular k+, tissue catabolism
• Serum K+ is high but total body K+ is low

Question 10

Anion gap

Answer 10

Consider un-measured anions

• Ketones
• Lactate
• Ethylene glycol
• Salicylate

Question 11

Sodium - influences in DKA

Answer 11

Water retention - acute kidney injury
Excessive water intake - polydipsia
Artefactual - high glucose

Question 12

AKI

Answer 12

• Urgent patient review

- GFR maybe compromised - low BP, shock (decreased blood flow to kidneys)

Question 13

What should be considered in AKI

Answer 13

• Obstruction, hydration, infection

- Drugs - most important that maybe harmful to kidneys: ACEI/ARB, NSAID, Diuretics

Question 14

Waste products that accumulate in AKI

Answer 14

• Creatinine, urea, acid

Question 15

Management of DKA

Answer 15

• Probs dehydrated - fluid saline
• Review drugs: ACEI/ARB. NSAID, Diuretics
• BP
• Monitor urine output
• Saline + insulin
• Monitor Na, K, HCO3, eGFR, glucose

Question 16

Complications of AKI

Answer 16

- Volume overload, raised K+, H+, PO4  
Initial assessment: 
- Volume status - possible dehydration, CHF 
- s-K, HCO3, PO4, calcium, albumin 
- s-uric acid, magnesium 
- FBC

Question 17

Glomerular disease

Answer 17

Manifest in a variety of ways ranging from:

• Aymptomatic urinary abnormalities
• Acute kidney injury (AKI)
• End-stage kidney disease

Question 18

Glomerular disease clinical manifestations

Answer 18

• Glomerular basement membrane (GBM)
• Barrier to the passage of macromolecules (both size- and charge-selective)
  Clinical manifestations:
• Hematuria and/or albuminuria/proteinuria
• Kidney insufficiency
• Hypertension
• Oedema etc

Question 19

Albuminuria - proteinuria

Answer 19

Change in clinical use

• From proteinuria
• To albuminuria

Urine albumin measurements improved
Urine protein measurements more variable
Diabetes kidney disease research used albuminuria

Question 20

Identification of albuminuria

Answer 20

• Urine dipstick
• Quantitative measurement of urine albumin excretion
• Usually as ACR - albumin creatinine ratio
• ACR allows for differences in urine concentration

Question 21

Persistent albuminuria categories urine ACR (mg/mmol) description and range

Answer 21

A1 - normal male<2.5 female<3.5
A2 - microalbuminuria male 2.5-25. female 3.5 - 35
A3 - macroalbuminuria male > 25 female > 35

Question 22

eGFR categories (mL/min/1.73 min^2) Description and range

Answer 22

G1 Normal or high >90
G2 Mildly decreased 60-89
G3a Mildly to moderately decreased 45-59
G3b Moderately to severely decreased 30-44
G4 Severely decreased 15-29
G5 Kidney failure <15

Question 23

Diabetic nephropathy - albuminuria

Answer 23

Major clinical manifestation is albuminuria

Moderately increased albuminuria - predicts high risk for future nephropathy

Question 24

Features of diabetic microvascular disease

Answer 24

• Nephropathy, retinopathy, neuropathy

Question 25

Risk factor for diabetic microvascular disease

Answer 25

- Hypertension

Question 26

Nephrotic syndrome

Answer 26

``` Urine albumin loss - Low serum albumin Low oncotic pressure stimulates - Liver albumin synthesis - also lipoprotein synthesis - Hypercholesterolemia and hypertriglyceridemia Also synthesis clotting factors - thrombotic disease ```

Question 27

What is nephrotic syndrome defined by

Answer 27

- Heavy albuminuria ACR > 250 mg/mmol - ACR > 70 mg/mmol = 1g protein/24h - Protein excretion > 3.5g/24h - Low serum albumin <30 g/L

Question 28

What is ACR

Answer 28

Urine albumin to creatinine ratio, also known as urine microalbumin, helps identify kidney disease that can occur as a complication of diabetes

Question 29

Main way in which nitrogenous end products are excreted

Answer 29

- The kidneys are the main route by which nitrogenous end products are excreted - The loss of renal function is characterised by the increase of nitrogenous waste products in the blood - High protein intake will lead to increase of production of urea which must be filtered through the kidneys

Question 30

Urea origin

Answer 30

Protein - amino acids - urea Alanine -ALT-> urea + pyruvate Aspartate -AST-> urea + oxalo-acetate -> glucose ALT - Alanine transaminase AST - Aspartate transaminase Enhanced by stress - cortisol (glucocorticoid)

Question 31

Creatinine origin

Answer 31

``` Muscle mass - creatine - creatinine Creatine + ATP -ck-> Creatine-P + ADP Creatinine -constant decay-> creatinine CK - creatine kinase creatine-p - high energy phosphate ```

Question 32

Creatine kinase - CK

Answer 32

- Levels related to muscle mass - Women < men - Children < adults - Black africans - greater muscle mass - After physical exertion, increase - slight-moderate - If raised, repeat with 3 days with no exertion

Question 33

Kidney stones - types of stones

Answer 33

- 80pc are composed of calcium salts - Calcium oxalate - mc - Calcium phosphate - Uric acid - Ammonium - infection - Cysteine - inborn error - Xanthine - very rare - inborn error

Question 34

Causes of kidney stones - calcium related

Answer 34

Calcium - Primary hyperparathyroidism - Renal tubular acidosis - distal - High sodium intake Oxalate(hyperoxaluria) - Low calcium/high ovalate diet - Primary hyperoxaluria Low urine citrate - Rx potassium citrate

Question 35

Kidney stone causes - uric acid

Answer 35

``` Uric acid - high purine diet -Alcohol. Obesity, drugs Ammonium – infection Cystine – inborn error Xanthine – very rare – inborn error ```

Question 36

Kidney stones - investigations - serum

Answer 36

Fluid intake especially Hot environment Radiology – residual stones, nephrocalcinosis Urine culture Urine pH Serum sodium, potassium, chloride, bicarbonate, creatinine, calcium, albumin, phosphate, alkaline phosphatase, uric acid, vitamin D, PTH,

Question 37

Kidney stones - investigations - urine

Answer 37

- Volume, creatinine: fluid intake - Sodium - increases u-calcium - Calcium - Phosphate - Oxalate - diet, inborn error - - Citrate - helps solubilise calcium - Uric acid - xanthine, cystine (transport defect dibasic aa) - Albumin - rare

Question 38

RTA - renal tubular acidosis - distal

Answer 38

- Nephrocalcinosis/kidney stones | - Bone disease in older age

Question 39

Diagnosis RTA

Answer 39

- s-potassium usually low - Metabolic acidosis - normal anion gap - Increased s-chloride - Inappropriately alkaline urine - Clinical context - Urine pH, citrate, bicarbonate - Urine acidification test

Question 40

Treatment of RTA - distal

Answer 40

- Rx - potassium citrate | - correct acidosis, potassium