Table of Contents
- detects both free Hb (or myoglobin) and Hb within RBCs, although is more sensitive for the former.
- normal individuals pass up to 1 million RBC's/24hrs in their urine which equates to ⇐ 5RBC's/hpf.
- as little as 1ml of blood per litre urine may cause grossly appreciable haematuria
- it may detect as few as 3 RBC's/hpf (high power field), but may fail to detect up to 15% of pts with microscopic haematuria defined as being > 5RBC's/hpf
- see also haematuria
causes of false negative tests:
- substances that alter the Hb molecule (eg. large amounts of urinary vitamin C)
- dilute urine
- large amounts of proteinuria
causes of false positive tests:
- chlorine or other oxidising agents
- if positive then microscopy should be done (unless it is obviously contamination - eg. menstruating females in which case consider recollection with tampon in situ & careful attention to technique):
- if no RBC's then this suggests free Hb or myoglobin
- if RBC's, determine whether glomerular in origin or not
- if proteinuria is present then consider urinary protein electrophoresis to detect non-albumin proteins.
- can detect protein at 10-15mg/dL but does not reliably yield positive results until [ ] > 30mg/dL
- correlation between color intensity & concentration is only approximate
- 3-5x more sensitive to albumin than to globulins & Ig light chains (Bence Jones protein), an important limitation.
- alkaline urine
- prolonged immersion of dipstick in urine
sulphosalicylic acid (SSA) test:
- more sensitive, can detect 5mg/dL of albumin or non-albumin protein
- 8 drops of 20% SSA added to 2ml urine ⇒ if turbid then +ve for protein
- radiographic contrast agents
- sulphonylurea drugs
- alkaline urine
- during 24 hours, kidneys normally filter 180L of plasma containing 12kg of protein. The 1-2L of urine produced from this filtrate contains only 40-80mg of protein in normal individuals.
- abnormal proteinuria is defined as excretion of > 150mg/24hr in adults or > 140mg/m2/24hr in children.
- the more common type, results from increased permeability of glomerular capillaries to plasma proteins
- contains both albumin & globulins
- may cause 10g protein loss per day or more & lead to the nephrotic syndrome (>3.5g/day)
- occurs in pts with normal glomeruli when the smaller proteins that are normally filtered at the glomerulus & then reabsorbed in the tubule appear in the urine because of tubular or interstitial abnormality.
- eg. urinary tract obstruction, HbS, & other causes of acute or chronic interstitial nephritis
- daily losses rarely exceed 2g
- urinary loss of small proteins that are present in blood in excessive concentrations which thus overload the tubular reabsorptive capacity
- eg. light chains in multiple myeloma
miscellaneous causes of transient proteinuria:
- exertion, stress, fever
- pregnancy (up to 300mg protein/day in normal pregnancy - greater than this suggests pre-eclampsia)
- occurs in some pts during upright posture periods only, rarely > 2g/day
- examine as soon as possible after voiding otherwise structures such as red cell casts may disintegrate with time
- 10ml urine placed in conical tube, spun at 2000rpm for 5 mins and supernatant discarded, sediment is resuspended in residual urine & a drop is placed on a slide, & covered with a cover slip.
- casts tend to concentrate at the periphery of the slide & thus this section is scanned at low power
- slide is then scanned at high power for RBC's, WBC's, renal tubular epithelial cells, oval fat bodies, bacteria & crystals
- observations are recorded as number of cells seen per high power field - normal RBC counts:
- 2-3 RBC's/hpf in adult men & 2-4 RBC's/hpf in adult women.
- are formed from urinary Tamm-Horsfall protein, a product of tubular epithelial cells that gels at low pH and high concentration & when mixed with albumin, RBC's, tubular cells, or cellular debris. The composition of a cast thus reflects the contents of the tubule.
casts are described according to their appearance & contents:
- devoid of contents
- seen with dehydration, exercise, or in association with glomerular proteinuria
- indicate glomerular haematuria as seen in glomerulonephritis
- imply the presence of renal parenchymal inflammation:
- interstitial nephritis (if eosinophilic cell on staining then suggests allergic aetiology)
- papillary necrosis
- composed of cellular remnants & debris
- occur in ATN
- like oval fat bodies, are generally assoc. with heavy proteinuria & the nephrotic syndrome, but have been noted to occur in a substantial proportion of pts with non-glomerular renal disease too.
- if casts are broad (> 3WBC diameters wide) then this suggests chronic renal disease with enlargement of the still functioning nephrons.
- suggest uric acid nephropathy but are extremely non-specific
oxalic acid or hippuric acid:
- may be seen in ethylene glycol ingestion
pa_urinalysis.txt · Last modified: 2014/01/02 05:03 by 127.0.0.1