U&Es interpretation

Question 1

Creatinine

Answer 1

Changes in serum creatinine are specific for determining kidney injury, but baseline levels depend on muscle mass

Question 2

Urea

Answer 2

Serum urea also rises in kidney injury but it is not specific for this

High urea - dehydration, GI bleeding, increased protein breakdown (trauma, infection, malignancy), high protein intake
Low urea - malnutrition, liver disease, pregnancy

Question 3

AKI - all patients need

Answer 3

Urine dip
Bloods: FBC, U&Es, CRP, calcium, phosphate, PTH
VBG - check for metabolic acidosis / alkalosis and hyperkalaemia
Accurate fluid balance chart
Stopping of any renal - excreted / nephrotoxic drugs

Question 4

Pre-renal failure (70%) - renal hypoperfusion

Answer 4

Causes: hypovolaemia / sepsis, renovascular disease, cardiorenal failure

Suggested by: hx, dehydration, hypotension, rise in urea greater than rise in creatinine

Investigation: hydration status assessment, renal artery doppler

Tx: tx cause and IV fluids
Complications - ATN

Question 5

Intrinsic renal failure (20%) - renal damage

Answer 5

Causes: ATN, GN, acute interstitial nephritis
Suggested by: causative drugs, renal hypoperfusion, other GN symptoms, haem and proteinuria

Investigations: urine dip, urine PCR, nephritic screen (if suspect GN), myeloma screen, creatinine kinase, renal biopsy
Tx - tx cause, stop causative agents, corticosteroids, acei and diuretics may be required for GN
Complications - irreversible renal damage

Question 6

Post-renal failure (10%) - obstruction

Answer 6

Cause:
Ureters - ureteric calculi, vesico-ureteric reflux, ureteric stricture, tumour, extrinsic compression
Bladder - neurogenic bladder, bladder calculi, tumour
Urethra - BPH, prostate cancer, stricture, blocked catheter

Suggested: history, urea and creatinine raised in equal proportion
Investigation - bladder scan, renal tract USS
Tx - relieve obstruction and tx cause
Complications - hydronephrosis

Question 7

Dialysis indications in AKI

Answer 7

Acidosis pH < 7.1
Electrolyte abnormalities (hyperkalaemia, hyponatraemia, hypercalcaemia) - K > 6.5 or ECG changes
Intoxicants (methanol, lithium, salicylates)
Overload - acute PO
Uraemia - urea > 60, uraemic pericarditis or encephalopathy

Question 8

CKD

Answer 8

Presence of marker of decreased kidney damage or decreased GFR for > 3 months

Commonest causes - diabetes, HTN, chronic GN, PKD

Determining cause - hx, urine dip, renal USS, biopsy

Management - manage cause, fluid restriction, dietary protein restriction, ACEi, tx complications, dialysis

Question 9

Hyponatraemia - nausea / vomiting, headache, confusion, seizures

Answer 9

Investigations:
Plasma osmolality to confirm if true hyponatraemia
Low = true
Normal = false 
High = dilutional (due to high glucose)

Urinary sodium and osmolality (to determine whether the problem is occuring in the kidneys or elsewhere)

Specific tests to confirm cause e.g. Addison’s, SIADH (low plasma osmolality and high urine osmolality), hypothyroidism

Question 10

Hypernatraemia - thirst, confusion, muscle twitching / spasms

Answer 10

Euvolaemic = iatrogenic
Hypovolaemic:
Producing small volumes of concentrated urine - dehydration
Not producing small volumes of concentrated urine - DI, osmotic diuresis (e.g. DKA)

Investigation - urine and serum osmolality, fluid deprivation test

Management - tx cause, sodium correction with fluids

Question 11

Hypokalaemia - arrhythmias, tremor, muscle weakness / cramps, constipation

Answer 11

Increased renal loss - diuretics, endocrinological (steroids cushing’s, conn’s), RTA, hypomagnesaemia
Intestinal loss - intestinal fluid loss
Increased cellular uptake - salbutamol, insulin, alkalosis

Tx cause
>2.5 - potassium supplements
< 2.5 - 40mmol/L potassium chloride in 1L 0.9% saline over 4-6 hours

Question 12

Hyperkalaemia - arrhythmias, lethargy, muscle weakness

Answer 12

Reduced renal excretion - acute / chronic kidney injury, drugs (potassium-sparing diuretics, ACEi, NSAIDs), aldosterone deficiency (Addison’s)
Excess K load - iatrogenic, massive blood transfusion
Release from intracellular fluid - acidosis, tissue breakdown

Question 13

Hyperkalaemia management

Answer 13

ECG and 3 lead cardiac monitoring - flat wide P waves, wide bizarre QRS, tall tented T waves
Calcium gluconate 10mL 10% IV over 10 mins - works in minutes, lasts 30-60mins
Actrarapid insulin: 10 u in 250mL 10% dextrose IV over 30 mins
Calcium resonium - give with regular lactulose

Consider HDx
Tx cause

Question 14

Hypocalcaemia - CATs go numb: convulsions, arrhythmias, tetany, numbness

Renal funciton
PTH
Phosphate, magnesium

Answer 14

Causes:
PTH deficiency (high phosphate, low PTH) - hypoparathyroidism, hypomagnesaemia, cinacelcet 

High PTH, low phosphate - vitamin D deficiency, bisphosphonates

High PTH, high phosphate - CKD, pseudohypoparathyroidism, rhabdomyolysis

Question 15

Hypocalcaemia management

Answer 15

Tx cause
Severe (< 1.9) or symptomatic - calcium gluconate 10 mL 10% IV over 10 mins
Mild (> 1.9) and asymptomatic - calcium supplements

Question 16

Hypercalcaemia - painful bones, renal stones, abdominal groans and psychic moans

Answer 16

PTH excess - primary or tertiary hyperparathyroidism, ectopic PTH production

Vitamin D excess - excessive vitamin D intake, sarcoidosis

Increased release from bone - bony metastasis (high ALP), myeloma (normal ALP), thyrotoxicosis

Other causes - drugs that decrease renal excretion

Dehydration also common cause (urea and albumin also likely raised)

Question 17

Hypercalcaemia investigations

Answer 17

Renal function, ALP, PTH, phosphate
Myeloma screen
Serum ACE
Isotope bone scan

Question 18

Hypercalcaemia management

Answer 18

Tx cause
Replace fluid deficit and keep pt well hydrated e.g. continuous saline 0.9% saline at 1L over 4-6 hours
If severe (>3.5 mmol/L) or symptomatic - bisphosphonate e.g. IV pamidronate 30-90mg

Question 19

Hypomagnesaemia - lethargy, muscle weakness / cramps, tremors, arrthymias, seizure

Answer 19

Excess loss - drugs, severe diarrhoea, DKA
Poor nutrition
Alcoholism

Often leads to hypokalaemia and hypocalcaemia

Correct before concurrent hypokalaemia or hypocalcaemia if possible. PO or IV options

Question 20

Hypophosphataemia - lethargy, muscle weakness, change in mental state

Answer 20

Vitamin D deficiency
Refeeding syndrome
Primary hyperparathyroidism 
Poor nutrition/ alcoholism / malabsorption 
Alkalosis 

PO or IV. Do not give if hypercalcaemic or oliguric.