Kidney function measurement

Question 1

creatinine clearance

Answer 1

uses creatinine urine (24hour). Take Urine conc*volume/plasma conc. Not generally used. Time consuming, collection issues, not corrected for body surface area

Question 2

Coccroft Gault

Answer 2

Uses patient agelean body weightsex dependent constant/creatining conc. Not corrected for body surface area
Not good for extremes of weight scale

Question 3

Modified MDRD

Answer 3

Corrected for BSA. Uses serum creatnine, age, sex and ethnicity. Do not need patient weight. Underestimates values >60mL/min. Not widely validated in ethnic groups, or elderly, or extremes of body habitus

Question 4

CKD-EPI

Answer 4

Uses sex, serum creatinine, age, ethnicity, and formula adjusted depending on creatinine elevation (therefore more accurate over wider range, since GFR and creatinine don’t have linear relationship. recommended by NICE and can report values up to 90

Question 5

Cystatin C

Answer 5

Small protein. Produced by all nucleated cells. Filtered and no secretion, but 100% reabsorbed (therefore should be 0%)
Not affected by muscle mass/fiet, can be combined with creatinine for accurate GFR. But, affected by obesity, thyroid, diabetes, coritocosteroids, inflammation, smoking and not widely available (expensive).
NICE says consider with eGFR creatinine 45-59, and no proteinuria, and if eGFR cystatin C >60 then no CKD

Question 6

AKI/CKD urine dip normal

Answer 6

Tends to be problem with kidney perfusion (pre renal aki/renovascular) or obstruction post kidney (postrenal AKI)

Question 7

AKI/CKD urine dip Blood and protein

Answer 7

Nephritis syndrome, glomerulonephritis, vasculitis, ATN

Question 8

AKI/CKD urine dip Protein only

Answer 8

Glomerulonephropathy, nephrotic syndrome

Question 9

AKI/CKD urine dip Blood only

Answer 9

Urological, rhabdomyloysis, ATN, glomerulonephritis

Question 10

Dipstick for UTI in elderly?

Answer 10

No, risk of FP. Must get urine culture

Question 11

Proteinuria quantification

Answer 11

Dipstick is qualitative only, gold standard is 24hour collection, but can use random urine total protein:creatinine, random urine albumin:creatinine (preferred as more specific) (both of these give indication of how concentrated urine is)

Question 12

Relationship between ACR or protein:creatinine ratio mg/mmol ->mg/day?

Answer 12

multiply by 10

Question 13

CKD diagnosed?

Answer 13

(KDIGO guidelines) CKD is classified by GFR (<60) and or albuminuria. Has stages 1,2,3a,3b,4,5

Question 14

Other Renal tests?

Answer 14

Urea, serum albumin, Hb, calcium/phosphate/PTH, immunology

Question 15

Renal biopsy indications?

Answer 15

Acute kidney injury (esp RPGN), nephrotic syndrome, chronic kidney kisease in association with proteinuria

Question 16

Kidney imagine

Answer 16

plain Xray not used much, but can sometimes show stones. U/S widely use (safe, easy and can show stenosis by smaller kidney), but is user dependent and obese patients can be difficult. CT scan quick, no contrast and excellent resolution (but queues and has radiation exposure). CT renal angiogram can be used to visualise blood vessels.