Clinical significance

1. normal value: the normal range of sp.gr. from 1.008 to 1.030, but usually it is within the limits of 1.015 to 1.025.

Note:the sp.gr. varies inversely with the volume of urine excreted thus, in D.insipidus the sp.gr. is very low, approaching 1.001, where large volume is excreted, whereas, in febrile conditions, a smaller volume is excreted, the urine is concentrated and has a high sp.gr.

An exception to the inverse ratio is D.mellitus; in this condition the volume is usually large and the sp.gr. is high because of the glucose present.

2. high sp.gr.: provided renal function is normal, urine of high sp.gr. is excreted when

(i) fluid intake is restricted,

(ii)extrarenal fluid loss exceeds the intake,

(iii)presence of glucose in urine increases sp.gr., e.g.D.mellitus,

(iv)presence of albumin (albuminuria) also increases sp.gr.

3. low sp.gr: urine of low sp.gr. is excreted when there is:

(i) polyuria with the exception of D.M. (see above),

(ii)the continued excretion of urine with low sp.gr. of 1.002 to 1.003 is characteristic of diabetes insipidus.

4. fixation of sp.gr.: normally, urine excreted at night has a higher sp.gr. than that secreted during the day. A considerable diurnal variation also seen throughout the day.

A constancy or “fixation” of the sp.gr. over any appreciable length of time is considered a sign of abnormal renal function.

In the later stages of chronic glomerulonephritis tubular function is so impaired that the kidneys are unable to concentrate or dilute urine which has a constant sp.gr. between 1.008 to 1.012 (average 1.010).

Estimation of total solids by sp.gr. Normal value: an adult excretes approximately 30 to 70 gms (average 60gms) of urinary solids in 24 hours.

Out of this –

(a) 35 gms is organic substances. Chief organic compounds: urea = 25 to 35gms per 24hrs.; uric acid = 0.5 to 1.0gm per 24hrs.; creatinine = 1.2 to 1.7gm per 24hrs.

(b) 25gms constitute inorganic compounds

IV. Acidity and pH

Urinary acidity may be expressed in 2 ways – (a) its H+ ion concentration (“true acidity”) and (b) titratable acidity.

pH of normal urine

Under ordinary conditions, ranges from 5.0 to 7.0, averaging 6.0 in mixed 24hrs urine sample.

<== попередня сторінка	\|	наступна сторінка ==>
II. Colour	\|	Clinical Significance

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