1. Investigations Of The Renal System
By:
Dr. Wael Thanoon Younis
C.A.B.M.,Mosul college of medicine.

2. Glomerular filtration rate:
The glomerular filtration rate (GFR) is the rate at which fluid passes into nephrons after filtration and is a measure of renal function. It is proportionate to body size and the reference range is usually expressed after correction for body surface area as 120 ± 25 mL/min/1.73 m2. The GFR may be measured directly by injecting and measuring the clearance of compounds such as inulin or radiolabelled ethylenediamine­ tetracetic acid, which are completely filtered at the glomerulus and are not secreted or reabsorbed by the renal. However, this is not performed routinely nstead, GFR is usually indirectly assessed in clinical practice by measuring serum levels of endogenously produced compounds that are excreted by the kidney.

3. The most widely used is serum creatinine, which is produced by muscle at a constant rate, is almost completely filtered at the glomer­- ulus, and is not reabsorbed.

5. Urinalysis:
Screening for the presence of blood, protein, glucose, ketones, nitrates and leucocytes and to assess pH and osmolality of urine can be achieved by dipstick testing . Urine microscopy or flow cytometry can detect erythrocytes, which are indicative of bleeding from the urogenital tract (anywhere from kidney to tip of penis); dysmorphic erythrocytes, which suggest the presence of nephritis; red cell casts, indicative of glomer­ular disease; and crystals, which may be observed in patients with renal stone disease. It should be noted that calcium oxalate and urate crystals can sometimes be found in normal urine that has been left to stand, due to crystal formation ex vivo. The presence of leucocytes and bacteria in urine is indicative of renal tract infection. White cell casts are strongly suggestive of pyelonephri­tis.

6. Urine pH can provide diagnostic information in the assessment of renal tubular acidosis. Urine col­lection over a 24­hour period can be performed to measure excretion of solutes, such as calcium, oxalate and urate, in patients with recurrent renal stone disease. Proteinuria can also be measured on 24­hour collections but is usually now quantified by protein/creatinine ratio on spot urine samples.

7. Blood tests: Haematology:
A normochromic normocytic anaemia is common in CKD and is due in part to deficiency of erythropoietin and bone marrow suppression secondary to toxins retained in CKD. Other causes of anaemia include iron deficiency from urinary tract bleeding,decreased appetite, and haemolytic anaemia secondary to disorders such as haemolytic uraemic syndrome (HUS) and thrombotic thrombocyto­penic purpura (TTP).
Other abnormalities may be observed that reflect underlying disease processes, such as neutrophilia and raised erythrocyte sedimentation rate (ESR) in vasculitis or sepsis; lymphopenia and raised ESR in systemic lupus erythematosus (SLE); and fragmented red cells in HUS and TTP.

8. Biochemistry: Serum levels of creatinine may be raised, reflecting reduced GFR ,although serum cre­atinine values can remain within the reference range in patients with reduced muscle mass, even when the GFR has fallen by more than 50%. Serum levels of urea are often increased in kidney disease but this analyte has limited value as a measure of GFR since levels increase with protein intake, following gastrointestinal haemor­rhage and in catabolic states. Conversely, urea levels may be reduced in patients with liver failure or anorexia and in malnourished patients, independently of changes in renal function. Serum calcium tends to be reduced and phosphate increased in CKD, in association with high parathyroid hormone (PTH) levels caused by reduced production of 1,25(OH)2D by the kidney (sec­ondary hyperparathyroidism). In some patients, this may be accompanied by raised serum alkaline phos­ phatase levels, which are indicative of renal osteodystro­phy. Other biochemical abnormalities may be observed that reflect underlying disease processes, such as raised glucose and HbA1c levels in diabetes mellitus and raised levels of C­reactive protein (CRP) in sepsis and vasculitis.

9. Immunology:
Antinuclear antibodies and anti­double­stranded DNA antibodies may
be detected in patients with renal disease secondary to SLE.
Antineutrophil cytoplasmic antibodies (ANCA) may be detected in patients with glomerulo­nephritis secondary to systemic vasculitis ,as may antibodies to GBM in patients with Goodpasture’s syndrome and low levels of complement in SLE, systemic vasculitis and HUS and post infectious GN.

10. Imaging:
Ultrasound:
Renal ultrasound is a valuable non­invasive technique that is indicated to assess renal size and to investigate patients who are suspected of having obstruction of the urinary tract or renal tumours, cysts or stones.
Doppler imaging can be used to study blood flow in extrarenal
and larger intrarenal vessels.

11. Computed tomography: Computed tomography urography (CTU) is used to evaluate cysts and mass lesions in the kidney or filling defects within the collecting systems,with or without contrast medium. Computed tomography and angiography: This technique (CT ­angiography) involves performing computed tomography, following an intravenous injec­tion of contrast medium, to obtain images of the renal vasculature. It produces high­quality images of the main renal vessels and is of value in patients who have suf­fered renal trauma and those with haemorrhage from the renal tract, and in the investigation of renal artery stenosis. Other vascular structures, such as angiomyo­lipomas and aneurysms, can also be detected.

13. Magnetic resonance imaging:
Magnetic resonance imaging (MRI) offers excellent reso­ lution and gives good distinction between different tissue types It is very useful for local staging of prostate, bladder and penile cancers.
Magnetic resonance angiography (MRA) provides an alternative to CT­ angiography for imaging renal vessels but involves administration of gadolinium ­based con­trast media, which may carry risks for patients with impaired renal function.

14. Renal arteriography:
Renal arteriography involves taking X­rays following an injection of contrast medium directly into the renal artery. The main indication is to investigate renal artery stenosis or haemorrhage.
Renal angiography can often be combined with therapeutic balloon dilatation or stenting of the renal artery and can be used to occlude bleeding vessels and arteriovenous fistulae by the inser­tion of thin platinum wires (coils).These curl up within the vessel and promote thrombosis, thereby securing haemostasis.

15. Intravenous urography:
Intravenous urography (IVU) involves taking serial
plain X-­rays immediately before and after an intra­
venous injection of contrast medium. It has largely been
replaced by ultrasound, CTKUB and CTU for most renal
imaging purposes but remains a useful method of
viewing the renal papillae, stones and urothelial malig­
Nancies.

18. Pyelography:
Pyelography involves direct injection of contrast medium into the collecting system from above or below.
It offers the best views of the collecting system and upper tract, and is sometimes used to identify the cause of urinary tract obstruction.

19. Radionuclide studies: These are functional studies requiring the injection of gamma ray­emitting radiopharmaceuticals that are taken up and excreted by the kidney, a process that can be monitored by an external gamma camera.

20. Renal biopsy:
Renal biopsy is used to establish the nature and extent of renal disease in order to judge the prognosis and need for treatment . The procedure is performed transcutaneously with ultrasound or contrast radiogra­phy guidance to ensure accurate needle placement into a renal pole. Light microscopy, electron microscopy and immunohistological assessment of the specimen may all be required.

22. Any questions??? Thank you.