3. Specific gravity should reach 1.025 or more. In some patients with edema, nocturnal diuresis will invalidate the test. Dilution Test (Water Test) It is contraindicated in patients with renal/cardiac edema. The test may be modified for use in the diagnosis of adrenal

 

¾ Casts may not be found even if proteinuria is heavy

because of dilute urine or because pH is alkaline

¾ In cylindruria, large numbers of casts are seen, but

there may not be any protein in the urine.

Granular Casts

Normal Value

Occasional granular cast may be seen.

Granular casts result from the disintegration of the

cellular material of WBCs and epithelial cells into coarse

and fine particles.

Clinical Relevance

¾ Acute tubular necrosis

¾ Advanced glomerulonephritis

¾ Pyelonephritis

¾ Malignant nephrosclerosis

¾ Chronic lead poisoning.

Waxy Cysts

Never seen in healthy subjects. Seen in terminal diseases

of kidney.

¾ Chronic renal disease

¾ Tubular inflammation and degeneration.

Oval Fat Bodies and Fatty Casts (Fig. 5.30)

Never seen in urines of healthy individuals. In nephrotic

syndrome, fat accumulates in the tubular cells and eventually

sloughs off, forming oval fat bodies. This fat is probably a

cholesterol ester. Fatty casts usually composed of individual

droplets. The presence of fat droplets, oval fat bodies, or fatty

casts is the hallmark of the nephrotic syndrome.

Clinical Relevance

Fatty casts are found in chronic renal disease and indicate

tubular inflammation and degeneration.

Crystals

Crystals Seen in Normal Acid Urine (Fig. 5.31)

1. Amorphous urates: Yellow-red granules.

FIG. 5.30: Oval fat body

2. Uric acid: Yellow or red-brown irregular but usually

whetstone crystals or rhomboids.

3. Calcium oxalate: Refractile, octahedral “envelopes”.

Crystals Seen in Normal Alkaline Urine (Fig. 5.32)

1. Amorphous phosphates: Fine precipitate.

2. Triple phosphate: Colorless, three to six-sided prisms.

Occasionally fern leaf.

3. Ammonium biurate: Yellow brown spheres “thorn

apple”.

4. Calcium phosphate: Stellate prisms.

5. Calcium carbonate: Colorless spheres or dumb-bells,

tiny.

Crystals Seen in Abnormal Urine

1. Cystine: Colorless, refractile, hexagonal plate.

2. Tyrosine: Fine needles arranged in sheaves or clumps,

usually yellow, silky.

3. Leucine: Yellow, oily appearing spheres with radial

and concentric striations.

4. Sulfonamide crystals (sulfadiazine): Yellow-brown

asymmetrical, striated sheaves and round forms with

radial striations.

Cholesterol appears as flat notched plates in acid urine,

calcium oxalate and calcium hydrogen phosphate crystals

are found in neutral urine. Uric acid and urates redissolve

on warming at 60oC. Ampicillin is occasionally seen as

masses of long, tiny colorless crystals in acid urine when

given parenterally.

Other miscellaneous incidental findings observed on

microscopic examination of urinary sediment are shown

in Figure 5.33.

100 Concise Book of Medical Laboratory Technology: Methods and Interpretations FIGS 5.31A TO I: Crystals, etc. usually found in acidic urine: (A) Amorphous urates; (B) Uric acid; (C) Cholesterol; (D) Calcium oxalate crystal;

(E) Sodium urate; (F) Cystine crystal; (G) Fat droplets as seen in polarising light; (H) Leucin spheres; and (I) Tyrosine needles

A A

C

G H I

D E F

B

FIGS 5.32A TO E: Crystals usually found in alkaline urine: (A) Amorphous phosphate; (B) Calcium carbonate; (C) Triple phosphate in urine;

(D) Calcium phosphate; and (E) Ammonium urate crystals in urine

A B C

D E

Urine Analysis 101

FIGS 5.33A TO G: (A) Pollen; (B) Bacteria in urine; (C) Cloth fiber in urine; (D) Bilirubin crystals; (E) Bladder epithelial cells (these cells are

atypical); (F) Starch; (G) Calcium oxalate monohydrate crystals

A AB C D

AE F G

Bacteria, Fungus and Parasites

Bacteria may or may not (contaminated, overgrown) be

important. A dry film may be made by spreading a drop or

two of the urine sediment on a glass slide, fixed and stained

with Gram’s stain. If bacteria are identified in an uncentrifuged specimen under an oil immersion lens, it suggests

that more than 100,000 organisms/mL are present, i.e.

significant bacteriuria.

Acid-fast bacilli may be seen but urine should always be

cultured as smegma also contains some acid-fast bacilli.

Yeast cells may be seen in UTI (e.g. in diabetes mellitus)

but yeasts are also common contaminants (Fig. 5.34).

Parasites and Parasitic Ova

These may be seen as fecal or vaginal contaminants.

In Schistosoma haematobium, typical ova may be seen

in urine accompanied by RBCs from urinary bladder.

Trichomonas vaginalis may come from vagina when

urethral or bladder infection is suspected, the protozoa

should be searched for immediately in a wet preparation.

Spermatozoa are generally present in the urine of men

after nocturnal emissions (Fig. 5.35).

Casts in Urine: Common Causes

Hyaline

¾ Normal people after strenuous exercise

¾ Congestive heart failure

¾ Diabetic nephropathy

¾ Chronic renal failure

¾ Glomerulonephritis and pyelonephritis.

Red Cell

¾ Acute glomerulonephritis

¾ Lupus nephritis

102 Concise Book of Medical Laboratory Technology: Methods and Interpretations FIGS 5.34A TO C: (A) Fungi seen in urine candida; (B) Fungi seen in another photomicrograph; (C) Fungal contaminants in urine

A AB C

TABLE 5.7: Common patterns of abnormal urine composition in disease

Disease Daily

volume

Color Sp Gr Protein Red cell Casts Microscopic and other findings

Normal 600–2500 Yellow amber 1.003 1.030 0-trace 0 to Occ 0 to Occ Hyaline, casts, must be acid and

fresh or preserved

Hyperpyrexia Decreased Amber Increased Trace to+ 0 to + None to few Hyaline casts, tubular cells

Congestive heart

failure

↓ Amber ↑-varies with

renal function

1–2+ None to + + Hyaline and granular casts

Eclampsia ↓ Amber ↑ 3–4+ None to + 3-4+ Hyaline casts

Diabetic coma ↓ or ↑ Light ↑ + 0 None to + Hyaline casts, glucose, ketonuria

Acute glomerulonephritis

(Ac. GN)

 ↓ Smoky red ↑ 2–4+ 1–4+ 2–4+ Blood, cellular, granular, hyaline

casts, renal, tubular epithelium

Degenerative

phase (De. GN)

 Normal

or ↓

Light Normal

or ↑

4 + 1–2 + 4+ Granular, waxy, fatty casts,

broad casts

Lipoid nephrosis ↓ Light

to dark

Very high 4+ O to trace 4+ Hyaline, granular, fatty, waxy

casts, fatty tubule cells

Collagen disease Normal, ↓

or ↑

Light to dark Normal or ↓ 1–4+ 1–4+ 1–4+ Blood, cellular, granular, hyaline,

waxy, fatty, broad casts, fatty

tubule cells

Pyelonephritis Normal

or ↑

Cloudy, dark Normal or ↓ 1–2+ None to+ None to+ Pus casts and hyaline casts.

Many pus cells, bacteria

Benign

hypertension

Normal or

↑

Normal or

Light

Normal or ↓ None to+ 0 to trace None to+ Hyaline and granular casts

Malignant

hypertension

Normal ↓

or ↑

Light Low, fixed 1–2+ Trace to+ 1–2+ Hyaline and granular casts

Occ = Occasional ↓ = Reduced or decreased ↑ = Increased or raised 0= Nil/Zero

Urine Analysis 103

¾ Goodpasture’s syndrome

¾ Subacute bacterial endocarditis

¾ Renal infarction.

White Cell

¾ Acute pyelonephritis

¾ Interstitial nephritis

¾ Lupus nephritis.

Epithelial Cell

¾ Tubular necrosis

¾ Cytomegalovirus infection

¾ Toxicity from heavy metals, salicylates

¾ Transplant rejection.

Granular

¾ Nephrotic syndrome

¾ Pyelonephritis

¾ Glomerulonephritis

¾ Transplant rejection

¾ Lead toxicity.

Waxy Casts

¾ Severe tubular atrophy

¾ Renal failure.♥

FIGS 5.35A TO C: (A) Microfilaria; (B) Schistosoma haematobium; (C) Trichomonas vaginalis

6

Renal Function and

its Evaluation

C H A P T E R

Assessment of renal function involves urine analysis; both

routine and microscopic, blood chemistry, urography and

special renal function tests.

RENAL PHYSIOLOGY IN BRIEF

Each kidney contains about 1 million nephrons. A nephron

has a glomerulus and a long tubule that has three parts:

(1) the proximal convoluted tubule (PCT), (2) the thin loop

of Henle (LH), and (3) the distal convoluted tubule (DCT).

The glomeruli are the ultrafilter and the filtrate produced

is like plasma except that it has almost no protein, 180 liters

of this filtrate is produced in 24 hours, of which 178 liters

of water and most of the organic and inorganic solutes are

reabsorbed. Normally, some components of the filtered

solutes are actively absorbed (completely or almost so)—

glucose, phosphate and amino acids, sodium, etc. For some

solutes, such as glucose, phosphate and amino acids, the

maximum reabsorptive capacity of the tubule is limited

and filtered material in excess of this limit is passed on in

the urine. Normal renal threshold for glucose is 180 mg%,

if excess is presented to the nephron, it would result in

glycosuria. Other solutes are not reabsorbed, or are only

passively and partially reabsorbed or are actively secreted by

the tubule. Inulin (a carbohydrate) used for renal function

studies is not at all reabsorbed by the tubules. Some urea is

passively reabsorbed, but most of the filtered urea escapes

reabsorption. Exogenous creatinine, H+

, K+

, phenol red

(PSP), iodopyracet (Diodrast), para-aminohippurate and

penicillin are actively secreted by the tubule cells, thus

increasing excretion over the amount filtered.

FUNCTIONS OF THE KIDNEY

1. Removal in solution of solid waste substances (e.g.

end products of protein metabolism and foreign

substances like dyes).

2. Regulation of water balance.

3. Regulation of acid-base equilibrium and electrolyte

excretion. This includes secretion of H+

 and production

of ammonia from amino acids, principally glutamine.

The H+ and NH+ produced are exchanged for Na+ 4

in the DCT, thus providing for conservation of this

essential cation.

Urinalysis

This has already been dealt in depth in previous chapter

Impaired Renal Function and Blood Chemistry

1. Reduction in glomerular filtration rate or renal blood flow

is accompanied by a rise in blood urea nitrogen (BUN),

creatinine and non-protein nitrogen (NPN). Phosphate

and sulfate retention is common. These days newer

markers like cystatin c are available that reflect kidney

function better than the previously available tools.

2. Low serum protein concentrations occur commonly.

Edema may occur if serum albumin drops below 2.5

gm% or total serum proteins become less than 5.5 gm%.

3. Acid-base equilibrium is disturbed in nephritis.

Renal acidosis is partly due to failure to conserve

sodium during excretion of anions (e.g. chlorides and

phosphates).

4. Anemia accompanies chronic renal disease.

Renal Function and its Evaluation 105 CONCENTRATION: DILUTION TESTS

If the patient’s routine urine specimens contain no sugar

or protein and have a specific gravity of 1.025 or higher, a

concentration test is unnecessary.

Principle

Urine specific gravity is a measure of capacity of the

tubules to reabsorb water from glomerular filtrate, thus

concentrating the urine. Determination of osmolality

is better but equipment needed for this is generally not

available.

Concentration Test

It is contraindicated in uremia and is unreliable in a case of

heart failure with edema.

1. No fluids for 24 hours after the morning meal (uremic

patients are not to be dehydrated; they may have a

large obligatory renal water loss).

2. Collect urine specimens during the last 12 hours of the

period and determine specific gravity of each.

3. Specific gravity should reach 1.025 or more.

In some patients with edema, nocturnal diuresis will

invalidate the test.

Dilution Test (Water Test)

It is contraindicated in patients with renal/cardiac edema.

The test may be modified for use in the diagnosis of adrenal

insufficiency.

1. Evening meal as desired. Nothing orally after 8.00 pm.

2. At 8.00 am empty bladder and drink 1500 mL water

within 45 minutes.

3. Void every half an hour until noon (Save 8 specimens).

4. Specific gravity should be 1.003 in at least one of the

specimens.