The diagnostics and treatment of tropical diseases

by E. R. Stitt

The chemical analysis of the blood has attained a clinical simplicity and significance that demands recognition. It provides points of value in diagnosis, prognosis, and treatment, being especially useful in nephritis, diabetes, acidosis, comatose conditions, gout, and in questions of renal function and treatment, especially dietetic. Urine findings are always dependent upon kidney function, and, by blood chemistry, we can pass behind this barrier.

Few diseases have been as yet studied thoroughly in this respect, but our fund of knowledge is receiving constant additions. The field of tropical medicine is practically untouched, and it is quite possible that an investigation along this line might there yield facts of interest and value.

The following table (amplified from Myers), is a concise summary of normal findings and those encountered in various clinical conditions. The diagnostic significance is evident. Some of the results are based upon the analysis of many cases; others upon but few. One might include the findings mentioned elsewhere regarding acidosis in certain tropical diseases, but, except for such, we have no other data relative to them, unless one mentions that blood sugar is increased in the tropics. The values are given in milligrams per 100 cc. whole blood (the usual system), except those for diastatic activity (recorded in Winslow’s empirical units) and acidosis (expressed in terms of plasma carbon dioxide combining power—volumes %). “Inc.” and “Dec.” signify increased and decreased respectively.

Result of Chemical Examination of Blood

Condition	Non protein nitrogen	Urea nitrogen	Uric acid	Creat- inine	Sugar	Chole- sterin	Chlor- ides	Dias- tase	Plasma CO2 capacity
Normal	25-300	10-15	2-3	1-2	90-120	170-250	450-500	8-64	53-77
Diabetes mellitus, mild	..	..	..	..	150-300	..	..	Inc.	..
Diabetes mellitus, severe	..	20	4-10	2-4	300-1200	Inc.	Dec.	Inc.	10-50
Nephritis, acute	..	40-100	5-15	2-6	120-180	..	Inc.	..	20-45
Nephritis,interstitial, early	..	15-25	5-12	2-3.5	120-150	..	..	Inc.	..
Nephritis, interstitial, terminal	100-300	60-300	5-27	5-28	120-240	Inc.	Variable	Inc.	12-40
Nephritis, parenchymatous (nephrosis)	..	20-50	2-5	2-4	120-200	Inc.	Inc.	..	..
Nephritis, chronic diffuse, severe	..	to 230	to 10	to 16	to 250	..	..	..	..
Uraemia	90-350	70-300	..	..	..	..	..	..	..
Kidney polycystic, double	..	to 75	to 5	to 8	to 200	..	..	..	..
Prostatic obstruction	Inc.	12-40	3-9	1.5-3.5	110-160	..	..	..	..
Gout	..	..	4-10	..	..	..	..	..	..
Hyperthyroidism	..	Inc.	..	..	Inc.	..	..	Inc.	..
Hypoendocrine conditions	..	Dec.	..	..	60-90	..	Dec.	Dec.	..
Eclampsia	25-45	10-25	4-8	..	..	..	..	..	43-58
Intestinal obstruction, acute	75-170	45-120	Inc.	Inc.	..	..	..	..	..
Fever, acute	..	Inc.	Inc.	to 4	..	Dec.	Dec.	..	..
Pneumonia, severe and late	..	to 53	to 18	to 3.5	to 180	Inc.	Dec.	..	Dec.
Anaemia, pernicious	to 108	to 75	to 10	to 3.1	to 300	Dec.	Inc.	..	Dec.
Malignancy, late	Inc.	Inc.	Inc.	Inc.	..	Dec.	Inc.	..	Dec.
Dementia praecox, catatonic	..	6-10	Dec.	..	Inc.	..	..	..	..
Shock	Inc.	Inc.	..	Inc.	Inc.	..	..	..	Dec.
Bichloride of mercury poisoning	to 370	to 300	to 15	to 33	120-200	Inc.	..	..	..
Plumbism	Inc.	Inc.	Inc.	..	..	..	..	..	..

Interstitial nephritis is characterized by a nitrogen retention, while parenchymatous nephritis has relatively little nitrogen retention but does have a decided tendency towards chloride retention. Essential hypertonia with its normal blood chemistry is differentiated from arteriosclerosis with its frequent nitrogen retention. The imminence of uraemia may be judged by the extent of the nitrogen retention. We have an aid in the differentiation of the uraemia of nephritis accompanied by a flagging heart from the passive congestion of cardiac decompensation, especially as to which is the secondary condition, and thus therapeutic indications relative to mooted questions of treatment (hot packs, morphine, renal stimulants, etc.). Unsuspected cases of nephritis showing only gastric symptoms clinically have been detected by blood chemistry. The significance of albumin in traces and occasional casts in urine has been more definitely established by examination for increase of uric acid in the blood—an increase arguing for an organic lesion. Values of over 4 for creatinine do not occur without great impairment of renal function, and findings of more than 5 have practically uniformly foretold a fatal termination in less than six months, except in acute nephritis and mild bichloride of mercury poisoning. The creatinine is also the best guide to the status of renal function in terminal cases. The chloride and nitrogen content afford guides to diet.

The blood may indicate a prediabetic state, and place the practitioner upon his guard. There is a condition but recently recognized in which there is a normal blood sugar, a persistent glycuresis of usually less than 1% and independent of carbohydrate intake, occasionally polyuria, but with no other symptoms of diabetes mellitus. It is known as renal diabetes, is apparently harmless, probably not uncommon, and may represent the condition affecting most of those “diabetics” who can disregard diet with impunity. The blood sugar and plasma CO₂ are usually considered the only safe guides in the treatment of diabetes mellitus and no extended medical treatment or surgical interference should ever be attempted without their estimation. Glycosuria is a poor guide, especially in advanced cases.

In comatose conditions, nitrogen retention will indicate the uraemic, and hyperglycaemia the diabetic cases. But acute nephritis should always be borne in mind, as it may have a pronounced acidosis but no nitrogen retention.