renal diagnostics

What a urinalysis assesses

Color, clarity, odor, specific gravity, pH, glucose, ketones, protein, sediment

Best urine specimen

First voided morning urine (most concentrated)

24-hour urine collection

Measures total amount excreted in a day; used for hormones, creatinine, protein, urea, glucose

Urine culture & sensitivity

Identifies organisms and which drugs they are sensitive to; uses clean-catch in a sterile container

Normal urine odor

Slight odor from urea breaking down to ammonia

Normal urine color

Pale yellow to amber (urochrome pigments)

Brown to bright red urine

RBCs present

Cloudy urine

WBCs present

Dark yellow to orange urine

Concentrated urine

Normal urine specific gravity

1.003–1.030 (affected by cells, casts, microorganisms)

Urine osmolality vs specific gravity

Osmolality is more accurate for concentrating/diluting ability and NOT affected by solids

Normal serum creatinine

~0.7–1.5 mg/dL; reliable indicator of renal function

Creatinine–GFR relationship

GFR drops by half → creatinine doubles

Normal BUN

~10–20 mg/dL

BUN vs creatinine

BUN changes faster but is less specific

Things that raise BUN

Decreased renal function, low fluid volume, increased catabolism, high protein intake

BUN:creatinine ratio > 20:1

Suggests an acute GFR change (e.g., prerenal/dehydration)

Creatinine clearance

Estimates GFR using 24-hr urine + midpoint blood sample; not fully accurate, unreliable at low GFR

Inulin clearance (guide says 'insulin')

Most accurate GFR measure (freely filtered, not secreted or reabsorbed); expensive, must be injected

MDRD equation

Estimates GFR from creatinine and demographics; no urine collection

KUB

Plain abdominal x-ray; shows kidney size/shape/position, stones, foreign bodies, tumors; screening test

IVP

IV iodine dye + serial x-rays; evaluates structure and excretion

IVP nursing considerations

Dye is nephrotoxic and allergenic → keep patient hydrated; laxative/enema beforehand

Renogram

Radionuclide test best for FUNCTION (blood flow, GFR, tubular secretion)

Renal scan

Radionuclide test best for STRUCTURE; tumors/nonfunctioning areas show no uptake

PET/SPECT

Dynamic scintigraphic imaging; detects subtle changes like regional GFR differences

Renal ultrasound

Noninvasive, painless; shows anatomy and masses; tells a fluid-filled cyst from a solid tumor

Renal CT

More detail than ultrasound; IV contrast improves view; shows masses, vascular disorders, filling defects

Renal MRI

No x-rays or radioactive markers; images in all planes; more detail than CT

Purpose of renal biopsy

Get tissue to find the nature/extent of disease for diagnosis, management, prognosis

Indications for renal biopsy

Persistent proteinuria, kidney-origin hematuria, unexplained AKI, glomerular disease, renal masses, transplant rejection, systemic disease with renal involvement