role of clinical biochemistry in renal disease

Question 1

what is a U&E

Answer 1

serum conc of cr, urea, na, k

e-GFR via cr conc

Question 2

what is urine tested for

Answer 2

albumin-creatinine ratio
protein-creatinine ratio
range of supporting assays for AKI and CKD

Question 3

how is GFR calculated

Answer 3

(UXV)/S

Question 4

Why creatinine derived from creatinine in muscle

Answer 4

derived from creatinine in muscle
serum conc relatively stable 
24h urine output stable day to day
no absorption and little secretion 
simple to measure

Question 5

what affects creatinine

Answer 5

age
sex
lean body mass
effect of diet

Question 6

how are the variations in GFR varied

Answer 6

GFR related to body surface area - standardise to a given body surface area
allows for comparison against general standard, staging of renal disease, monitoring change in renal filtration

Question 7

how is glomerular function calculated

Answer 7

MDRD equation for e-GFR
allows for age, sex, ethnicity
age - dec GFR, largely offset by reducing muscle mass

Question 8

relationship between GFR and plasma creatinine

Answer 8

plasma creatinine inc exponentially (ish) as GFR dec

ref range creatinine can mean that GFR can dec sig before seen as abnormal

Question 9

what does high plasma glucose cause

Answer 9

osmotic diuresis leading to loss of water and sodium
failure of glucose metabolism - ketoacidosis (inc serum conc of K+ and PO43-)
enhanced by renal impairment

Question 10

what does vomiting result in

Answer 10

fluid loss

Question 11

what does loss and salt and water lead to

Answer 11

volume depletion leading to impaired renal function and dehydration

Question 12

how is dehydration assessed

Answer 12

likely if serum urea-creatinine greater than 100
passive reabsorption of urea in nephron at low flow rates
serum protein may also be high

Question 13

how is AKI detected

Answer 13

rise in serum cr of >26umol/L/48h
>50% serum cr in 7 days
fall in UO <0.5ml/kg/hr >6h adults/8h kids
>25% fall eGFR in <18 y/o’s

Question 14

what is the AKI alert system

Answer 14

alert if AKI likely nd stages
1 >1.5x baseline or >26umol/L in 48h
2 >2x baseline
3 >3x baseline or >1.5 to >354umol/L

Question 15

causes of AKI

Answer 15

poor perfusion - loss of isotonic fluids
sepsis - sev infection
toxins - drugs eg NSAIDs, ahminoglycosides, endogenous eg Hb, light chains
Obstruction - renal calculus, prostatic enlargement
parenchymal - glomerulonephritis

Question 16

how is Goodpasture’s syndrome treated

Answer 16

plasma exchange to remove antibody

Question 17

how is good pasture’s syndrome diagnosed

Answer 17

elevated cr, CRP
AKI alert 
proteinuria
anaemia, raised WBC
no anti-streptolysin titre
raised anti-GBM antibody

Question 18

what is not uncommon in boy builders

Answer 18

mild hypokalaemia

Question 19

what is the origin of creatinine

Answer 19

muscle mass - creatine - creatinine 
creatine + ATP + Creatine-P + ADP 
constant decay
creatinine 
CK - creatine kinase

Question 20

what does raised serum CRP indicate

Answer 20

septic condition

Question 21

causes of CKD

Answer 21

hypertension
diabetes (T2DM more)
hyperlipidaemia
renal infections
chronic glomerulonephritis (IgA nephritis)
system disease - lupus or myeloma
genetic - polycystic kidney, alport syndrome
chronic obstruction - prostate, calculi, reflux
medication - NSAID, Li

Question 22

what does ACR indicate

Answer 22

proteinuria common in RD

large proteins not long retained by glomerulus, same for albumin so escape into urine

Question 23

metabolic features of stage 2 CKD

Answer 23

elevated serum urea and creatinine conc

inc in PTH conc

Question 24

metabolic features of stage 3 CKD

Answer 24

calcium absorption decreased
lipoprotein lipase decreased
malnutrition
anaemia - less EPO

Question 25

metabolic features of stage 4 CKD

Answer 25

elevated serum TG and phosphate conc metabolic acidosis hyperaemia - elevated serum K

Question 26

metabolic features of stage 5 CKD

Answer 26

marked cr and urea conc, more marked other features aforementioned

Question 27

intervention for elevated urea

Answer 27

low protein diet

Question 28

intervention for hyperkalaemia

Answer 28

diet diuretics treat acidosis

Question 29

intervention for low bicarbonate

Answer 29

bicarbonate supplements

Question 30

intervention for low Hb

Answer 30

iron supplements with possible erythropoietin with target Hb 100-120 g/l

Question 31

intervention for low ferritin and transferrin sat

Answer 31

iron supplements with target sat >20% and ferritin 100-600

Question 32

low calcium intervention

Answer 32

reduced serum phosphate, vit D supplements (often 1-alpha OH vit D3)

Question 33

raised phosphate intervention

Answer 33

phosphate binding drugs

Question 34

raised PTH intervention

Answer 34

raised serum calcium, calcimimetic drugs to keep PTH 2-9 X upper limit of RI

Question 35

raised TG intervention

Answer 35

diet, weight reduction, fibre or statins

Question 36

what happens when interventions fail

Answer 36

dialysis | possible transplant

Question 37

role of lab in finding cause of AKI

Answer 37

plasma lactate - prognostic indicator infection - serum procalcitonin, CRP, WBC, blood culture AI

Question 38

role of lab in finding cause of CKD

Answer 38

serum and urine light chain - myeloma glycated Hb - diabetic control antibody tests - ANA, ANCA, anti-GBM biopsy - histology

Question 39

what are pre and post dialysis samples for

Answer 39

effectiveness requirement of frequency determine need for other interventions - diet, supplements, phosphate binders, calcimimetic drugs, lipid lowering agents, iron supplements/EPO

Question 40

how are renal transplant patients

Answer 40

``` serum cr - transplant function e-GFR ACR/PCR - potential damage to transplanted kidney anti-rejection drugs tubular dysfunction monitoring for CKD3 ```

Question 41

when is real GFR recognised

Answer 41

determine dose of renal excreted drugs that are potentially toxic monitoring dialysis and transplant patients cock-croft and Gault

Question 42

what is the cock-croft Gault measurement of GFR

Answer 42

individual measurement and used for calculating drug dosage

Question 43

treatment to reduce the risk of nephrocalcinosis/renal stone formation

Answer 43

potassium citrate sodium bicarbonate thiazide diuretics in RTA

Question 44

what is Fanconi syndrome

Answer 44

congenital and acquired condition elevated conc of AAs, calcium and phosphate RTA disorder

Question 45

what does the water deprivation test diagnose

Answer 45

post dehydration osmolality in serum and urine and post DDAVP osmolality normal, nephrogenic DI, cranial DI, chronic polydipsia For DI, RTA disorder