The serum anion gap, calculated from the electrolytes measured in the chemical laboratory, is defined as the sum of serum chloride and bicarbonate concentrations subtracted from the serum sodium concentration. This entity is used in the detection and analysis of acid-base disorders, assessment of quality control in the chemical laboratory, and detection of such disorders as multiple myeloma, bromide intoxication, and lithium intoxication. The normal value can vary widely, reflecting both differences in the methods that are used to measure its constituents and substantial interindividual variability. Low values most commonly indicate laboratory error or hypoalbuminemia but can denote the presence of a paraproteinemia or intoxication with lithium, bromide, or iodide. Elevated values most commonly indicate metabolic acidosis but can reflect laboratory error, metabolic alkalosis, hyperphosphatemia, or paraproteinemia. Metabolic acidosis can be divided into high anion and normal anion gap varieties, which can be present alone or concurrently. A presumed 1:1 stoichiometry between change in the serum anion gap (DeltaAG) and change in the serum bicarbonate concentration (DeltaHCO(3)(-)) has been used to uncover the concurrence of mixed metabolic acid-base disorders in patients with high anion gap acidosis. However, recent studies indicate variability in the DeltaAG/DeltaHCO(3)(-) in this disorder. This observation undercuts the ability to use this ratio alone to detect complex acid-base disorders, thus emphasizing the need to consider additional information to obtain the appropriate diagnosis. Despite these caveats, calculation of the serum anion gap remains an inexpensive and effective tool that aids detection of various acid-base disorders, hematologic malignancies, and intoxications.

Serum anion gap: its uses and limitations in clinical medicine.

Disorders associated with an altered anion gap

Despite the increasing therapeutic use of recombinant human growth hormone (rhGH), its metabolic clearance has not been investigated in detail. To evaluate the kinetics of rhGH as a possible function of GH plasma concentration and glomerular filtration rate (GFR), we investigated the steady state metabolic clearance rate (MCR), disappearance half-life, and apparent volume of distribution of rhGH at low and high physiological as well as supraphysiological plasma GH levels during pharmacological suppression of endogenous GH secretion in human subjects with normal and reduced renal function. GH in plasma and urine was determined by an immunoradiometric assay, and GFR by inulin clearance. In all subjects MCR decreased and plasma half-life increased with increasing plasma GH concentrations (P < 0.001). MCR of rhGH was approximately half in patients with chronic renal failure at each GH level and plasma half-life was increased by 25-50%. Allowing for the linear dependence of MCR on GFR and assuming single-compartment distribution, the estimated renal fraction of total MCR was 25-53 and 4-15% in controls and patients, respectively. Saturation of extrarenal disposal of GH was suggested by an inverse hyperbolic relationship between extrarenal MCR and plasma GH concentrations in all subjects. Fractional GH excretion was up to 1,000-fold higher in patients than in controls. We conclude that MCR of hGH is a function of plasma GH concentrations and GFR. Extrarenal elimination is saturable in the upper physiological range of GH concentrations, whereas renal MCR is independent of plasma GH levels. The kidney handles GH like a microprotein involving glomerular filtration, tubular reabsorption, and urinary excretion.

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Metabolic clearance of recombinant human growth hormone in health and chronic renal failure.

Potassium iodide (KI) is a useful drug in the dermatologic armamentarium. It is successfully used for inflammatory dermatoses, most notably erythema nodosum, subacute nodular migratory panniculitis, nodular vasculitis, erythema multiforme, and Sweet's syndrome. KI is also successfully used for cutaneous and lymphocutaneous sporotrichosis. The precise mechanism by which KI acts is unknown. Although many minor side effects are common with this drug, major side effects can occur in pregnant patients and those with a history of kidney or thyroid disease. This article reviews the pharmacology, mechanism of action, indications, contraindications, and adverse effects of KI as a therapeutic agent. (J Am Acad Dermatol 2000;43:691-7.)

Potassium iodide in dermatology: a 19th century drug for the 21st century-uses, pharmacology, adverse effects, and contraindications.

Objective— To review limitations of the use of serum anion gap in clinical practice Data Sources— Original reports and reviews Study Selection— Sources containing the most recent pertinent information Data Synthesis— Theoretical and practical limitations beset the use of serum anion gap Awareness of these limitations reduces but does not eliminate wrong diagnoses based on the anion gaps Conclusions— Serum anion gap has a limited value in the differential diagnosis of acid-base disorders and can be misleading ( Arch Intern Med 1992;152:1625-1629)

J S Cheigh

Papers

Iodide and negative anion gap.