Page 18 of 25

PA27.3-4 | Acute & Chronic Renal Failure — SDL Guide (Part 4)

AKI vs CKD — Distinguishing Features

Side-by-side educational diagram comparing AKI and CKD by onset, previous creatinine, kidney size, anaemia, calcium, and PTH changes. — **Panel A:** AKI: normal-to-enlarged kidneys; onset days to weeks; previous creatinine normal baseline; anaemia mild or absent early; calcium usually normal; PTH normal.. **Panel B:** CKD: small contracted kidneys; onset months to years with ≥3 months criterion; previous creatinine elevated on prior records; severe normocytic normochromic anaemia; calcium decreased; PTH increased; renal osteodystrophy; exceptions include DM, PKD, and amyloid..

Distinguishing AKI from CKD at presentation is a critical clinical-pathological skill:

Feature	AKI	CKD
Onset	Days to weeks	Months to years (≥3 months criterion)
Previous creatinine	Normal baseline	Elevated on prior records
Kidney size (USS)	Normal to enlarged	Small, contracted (except DM, PKD, amyloid)
Anaemia	Mild or absent (early)	Severe normocytic normochromic
Calcium	Usually normal	↓ (renal osteodystrophy)
PTH	Normal	↑ (secondary hyperparathyroidism)
Nails/neuropathy	Absent	Mees' lines, peripheral neuropathy
Renal biopsy	Tubular necrosis; recoverable	Glomerulosclerosis, fibrosis, atrophy — irreversible
Reversibility	Potentially full recovery	Irreversible; progressive

Important: AKI on CKD — a patient with pre-existing CKD may develop an acute insult (dehydration, sepsis, contrast) that worsens GFR acutely. Treating the acute component may restore to the CKD baseline (not normal). Always look for a reversible precipitant.

Management principles (brief):
- AKI: treat the cause (fluids for prerenal; remove nephrotoxins), prevent complications, renal replacement therapy (RRT) if AEIOU criteria met.
- CKD: slow progression (RAAS blockade, BP control, glycaemic control), manage complications (EPO for anaemia, vitamin D analogues + phosphate binders for bone disease, dietary K⁺/phosphate restriction), plan for RRT (haemodialysis, peritoneal dialysis, or transplant — the curative option).

⚑ AI image — pending faculty review (auto-QA score 7/10; best of 3 attempts)

Side-by-side infographic comparing AKI and CKD by kidney size, disease timeline, urine output pattern, laboratory findings, and end-stage CKD clinical clues. — **Panel A:** AKI column showing normal or enlarged smooth kidney, abrupt timeline, variable urine output, acute creatinine rise, initially normal haemoglobin, near-normal PTH, and near-normal calcium.. **Panel B:** CKD column showing small contracted granular kidney, long chronic timeline, early nocturia/polyuria with late oliguria, chronically high creatinine, low haemoglobin from decreased EPO, high PTH, and low or normal-low calcium.. **Bottom banner:** Clinical end-stage CKD clue showing bilateral 7.5 cm granular kidneys with thin cortices, Hb 7.0 g/dL, PTH 380 pg/mL, and management goal of slowing progression, treating uraemic complications, and planning dialysis or transplant..

SELF-CHECK

Ultrasound of a patient with renal failure shows both kidneys measuring 7.5 cm with granular surfaces and markedly thinned cortices. Haemoglobin is 7.0 g/dL, PTH is 380 pg/mL. Which diagnosis is most consistent, and what is the primary management goal?

A. AKI due to ATN; aggressive fluid resuscitation

B. Prerenal AKI; IV fluid challenge and recheck creatinine

C. Chronic kidney disease (likely end-stage); slow progression and plan renal replacement therapy

D. Polycystic kidney disease; genetic counselling

Reveal Answer

Answer: C. Chronic kidney disease (likely end-stage); slow progression and plan renal replacement therapy

Small contracted granular kidneys + severe anaemia (normocytic, ↓EPO) + markedly elevated PTH (secondary hyperparathyroidism from ↓vitamin D) are the classical triad of end-stage CKD. In AKI, kidneys are normal or enlarged and anaemia/osteodystrophy are absent or mild. PKD kidneys are massively enlarged, not contracted. Management now shifts to slowing any residual progression, managing uraemic complications, and planning haemodialysis/peritoneal dialysis or transplant referral.