THE ASSESSMENT OF RENAL FUNCTION

Assessment of renal function can be done by,

 Biochemical and immunological laboratory tests  

  Imaging and histological examination

Group I test:

a.      Routine urine examination

b.      Serum Creatinine

c.       Blood urea nitrogen

d.      Uric acid

 

These tests are helpful to differentiate pre-renal condition from renal and post renal conditions. They also give idea about the excretory function of kidney by measuring urea, creatinine, and uric acid. The normal ratio of urea nitrogen and serum creatinine is 14-24. Ratio >40 is seen during pre-renal cause of kidney disease where there is retention of BUN. In renal condition the ratio may be normal or <10 in case of tubular damage. In post renal condition where there is retention of urea and creatinine there will be proportional increase in both and ratio will be >14.

 a.      Urinalysis: This is the starting point of renal function assessment

Early morning samples are preferred as they are concentrated. The clean catch MSU is desirable. It must be analyzed within 1 hour of collection or refrigerated at 2-8⁰C for not more than 8 hours. If delayed in alalysis then bacterial multiplication will occur and urease producing organism will degrade urea to ammonia that alkalinize the pH. Loss of Carbondioxide by diffusion in air further elevates pH which cause cast degeneration and red-cell lysis. 

i.    Physical characters

Visual Appearance:

Normal transparency  –  transparent

Turbid                          –  UTI, proteinuria, fats (nephrotic syndrome)

Milky                            –  chyluria

Smoky                          –  hematuria during acute glomerulonephritis

Colour:

Normal color urine     – pale yellow mainly due to urochrome pigment (derivative or urobilin)

Pink orange                 – Haemoglobin, myoglobin, porphyrins

Blue-green                  –  pseudomonas infection, riboflavin

Brownish black            –  homogentisic acid (on standing), melanin, RBC

Wine color                  -   PKU

Odour:

Normal            –  Pungent due to aromatic acids.

Ammonical      –  UTI (presence of urea splitting microbes), contamination

Mousy                         –  MSUD

Fruity smell     –  Diabetic ketoacidosis

Volume:

Normal            – 750-2,000 mL/day average 1.5L per day.

Polyuria              – >3L/day occurs in diabetes mellitus and insipidus, chronic renal disease, acromegaly (over production of GH) and myxedema (hypothyroid  edema).

Anuria/oliguria –  <200 mL/day, found in nephritis, ESRD, urinary tract obstruction and ARF

pH

Normal            – slightly acidic around pH 6-7

Acidic                    – During acidosis, RTA, excretion of non volatile organic acids like     pyruvate, lactate, citrate

Alkalotic                 – UTI due to production ammonia form ammonium by bacteria, ingestion   of bicarbonate, Fanconi syndrome